1 00:00:00,160 --> 00:00:13,720 [Music] 2 00:00:19,160 --> 00:00:16,250 all of you in this room and I think 3 00:00:22,929 --> 00:00:19,170 actually every intelligent six-year-old 4 00:00:25,880 --> 00:00:22,939 knows that there is a record of life 5 00:00:28,130 --> 00:00:25,890 incorporated into sedimentary rocks the 6 00:00:31,009 --> 00:00:28,140 fossil record and we learn early that 7 00:00:34,639 --> 00:00:31,019 some time ago there were dinosaurs they 8 00:00:38,150 --> 00:00:34,649 were preceded by earlier tetrapod 9 00:00:40,549 --> 00:00:38,160 vertebrates that were preceded by fish 10 00:00:42,200 --> 00:00:40,559 and really intelligent six-year-olds 11 00:00:44,600 --> 00:00:42,210 note that there's also a record of 12 00:00:48,580 --> 00:00:44,610 marine life such as trilobite s-- and 13 00:00:53,330 --> 00:00:48,590 that this entire conventional record of 14 00:00:55,549 --> 00:00:53,340 tracks trails bones skeletons takes up 15 00:00:59,779 --> 00:00:55,559 what's called the phanerozoic era or the 16 00:01:02,330 --> 00:00:59,789 last 541 million years now if you look 17 00:01:05,149 --> 00:01:02,340 on the right the phanerozoic era is 18 00:01:07,520 --> 00:01:05,159 placed in the context of the geologic 19 00:01:09,859 --> 00:01:07,530 the age of the earth as a whole and 20 00:01:13,609 --> 00:01:09,869 we've heard a lot at this meeting about 21 00:01:18,109 --> 00:01:13,619 things that go on in the Hadean and 22 00:01:20,060 --> 00:01:18,119 Archaean eras that somehow must connect 23 00:01:22,550 --> 00:01:20,070 up to the things that people like Simon 24 00:01:25,280 --> 00:01:22,560 Conway Morris talked about which have 25 00:01:28,010 --> 00:01:25,290 their roots in in phanerozoic evolution 26 00:01:33,350 --> 00:01:28,020 and what connects those is the 27 00:01:35,090 --> 00:01:33,360 Proterozoic era and its record now there 28 00:01:37,429 --> 00:01:35,100 are two reasons why we might be 29 00:01:41,030 --> 00:01:37,439 interested in the Proterozoic one is for 30 00:01:43,160 --> 00:01:41,040 its own phenomenology this is an era 31 00:01:47,149 --> 00:01:43,170 nearly half of all recorded Earth 32 00:01:49,700 --> 00:01:47,159 history it begins or when it begins the 33 00:01:53,090 --> 00:01:49,710 earth basically has no oxygen in the 34 00:01:55,969 --> 00:01:53,100 atmosphere and has a biota made up of 35 00:01:58,700 --> 00:01:55,979 bacteria and archaea and by the time it 36 00:02:02,179 --> 00:01:58,710 ends we had a relatively oxygen-rich 37 00:02:04,520 --> 00:02:02,189 atmosphere that supports a biota that 38 00:02:07,760 --> 00:02:04,530 includes animals macroscopic seaweeds 39 00:02:09,410 --> 00:02:07,770 and the like between those both at the 40 00:02:12,080 --> 00:02:09,420 beginning and again toward the end of 41 00:02:12,590 --> 00:02:12,090 the Proterozoic era are as we heard 42 00:02:15,470 --> 00:02:12,600 yesterday 43 00:02:18,010 --> 00:02:15,480 they ice ages of a magnitude that is 44 00:02:23,720 --> 00:02:18,020 unknown over the last 500 million years 45 00:02:27,170 --> 00:02:23,730 also the emergence of eukaryotes as a 46 00:02:29,930 --> 00:02:27,180 major part of ecosystems so it's a rich 47 00:02:33,710 --> 00:02:29,940 record that I think one can look at for 48 00:02:36,980 --> 00:02:33,720 its own sake and at the same time it is 49 00:02:39,230 --> 00:02:36,990 a record that is much richer much more 50 00:02:41,480 --> 00:02:39,240 complete than the rather fragmentary 51 00:02:43,280 --> 00:02:41,490 record of the Archaean and therefore it 52 00:02:45,560 --> 00:02:43,290 can actually provide something of a 53 00:02:48,200 --> 00:02:45,570 template for thinking about how we might 54 00:02:51,380 --> 00:02:48,210 interpret the earlier record not to 55 00:02:54,410 --> 00:02:51,390 mention guide us in the exploration of 56 00:02:57,080 --> 00:02:54,420 sedimentary rocks on other planets now 57 00:02:59,830 --> 00:02:57,090 if the phanerozoic by definition and 58 00:03:03,080 --> 00:02:59,840 etymology is the record is the time of 59 00:03:06,140 --> 00:03:03,090 visible animals if we place that in the 60 00:03:08,360 --> 00:03:06,150 context of a molecular phylogeny and 61 00:03:10,610 --> 00:03:08,370 there's simply a notional phylogeny 62 00:03:14,690 --> 00:03:10,620 there and I understand that just about 63 00:03:16,670 --> 00:03:14,700 every note on this will be controversial 64 00:03:19,790 --> 00:03:16,680 to someone but I think everyone would 65 00:03:21,880 --> 00:03:19,800 agree that the animals that make up that 66 00:03:25,670 --> 00:03:21,890 conventional record of the phanerozoic 67 00:03:28,190 --> 00:03:25,680 constitute only the distal tips of one 68 00:03:31,100 --> 00:03:28,200 branch of the tree and that the deeper 69 00:03:34,280 --> 00:03:31,110 record and therefore the life that we 70 00:03:38,630 --> 00:03:34,290 might infer prior to the phanerozoic era 71 00:03:40,670 --> 00:03:38,640 is largely microbial so let's look at 72 00:03:44,540 --> 00:03:40,680 some sedimentary rocks from the 73 00:03:45,980 --> 00:03:44,550 proterozoic eon these are some rocks 74 00:03:48,320 --> 00:03:45,990 that when I was younger and fitter I 75 00:03:51,290 --> 00:03:48,330 worked on for a number of years these 76 00:03:53,900 --> 00:03:51,300 are carbonate rocks exposed in the 77 00:03:56,090 --> 00:03:53,910 Arctic island of Spitsbergen and what 78 00:03:59,060 --> 00:03:56,100 you're looking at there is about a 79 00:04:02,420 --> 00:03:59,070 thousand meters of carbonate rocks 80 00:04:05,930 --> 00:04:02,430 deposited between about 800 and 740 81 00:04:08,870 --> 00:04:05,940 million years ago there are no skeletons 82 00:04:11,990 --> 00:04:08,880 no bones no tracks or trails no evidence 83 00:04:13,910 --> 00:04:12,000 of animal life at all and so at this 84 00:04:16,190 --> 00:04:13,920 point the search for life becomes a 85 00:04:19,640 --> 00:04:16,200 practical one if we believe that the 86 00:04:22,280 --> 00:04:19,650 antecedent record was microbial should 87 00:04:25,340 --> 00:04:22,290 we expect the sedimentary rock record to 88 00:04:26,480 --> 00:04:25,350 preserve a tractable record of tiny 89 00:04:28,950 --> 00:04:26,490 micro or 90 00:04:31,830 --> 00:04:28,960 this also illustrates one of the 91 00:04:34,619 --> 00:04:31,840 advantages of essentially working out 92 00:04:37,019 --> 00:04:34,629 our rules of the game for exploring deep 93 00:04:40,379 --> 00:04:37,029 earth history that if you look at this 94 00:04:43,080 --> 00:04:40,389 pile of of carbonates if you would take 95 00:04:44,749 --> 00:04:43,090 all of the early Archaean carbonates 96 00:04:47,580 --> 00:04:44,759 that have ever been measured from 97 00:04:49,980 --> 00:04:47,590 basically everywhere in the world and 98 00:04:51,869 --> 00:04:49,990 stacked them on top of each other they 99 00:04:55,379 --> 00:04:51,879 would be about as thick as the little 100 00:04:57,659 --> 00:04:55,389 beige band right in the top of the black 101 00:05:00,570 --> 00:04:57,669 one at the corner of that picture so the 102 00:05:03,179 --> 00:05:00,580 record is indeed much richer and it is 103 00:05:06,089 --> 00:05:03,189 preserved rather differently so what do 104 00:05:08,760 --> 00:05:06,099 we see if we hone in on just one bed of 105 00:05:13,439 --> 00:05:08,770 those carbonates you can see here that 106 00:05:16,559 --> 00:05:13,449 there are these wavy laminated dolomite 107 00:05:18,420 --> 00:05:16,569 we know from just comparisons with the 108 00:05:21,119 --> 00:05:18,430 modern world where we can see processes 109 00:05:23,309 --> 00:05:21,129 in action that the kind of wavy textures 110 00:05:25,679 --> 00:05:23,319 that you see in that outcrop are 111 00:05:28,499 --> 00:05:25,689 generally associated with places where 112 00:05:30,420 --> 00:05:28,509 microbial mats interact with 113 00:05:33,990 --> 00:05:30,430 accumulating fine-grained carbonate 114 00:05:36,360 --> 00:05:34,000 sediments that tends to happen in 115 00:05:39,149 --> 00:05:36,370 coastal environments and we can see it 116 00:05:40,920 --> 00:05:39,159 in places like the Bahamas today if you 117 00:05:43,019 --> 00:05:40,930 look in the upper center of that picture 118 00:05:45,420 --> 00:05:43,029 you'll see something that's bowed up in 119 00:05:47,189 --> 00:05:45,430 the button-down parlance of geologists 120 00:05:49,760 --> 00:05:47,199 that's called a teepee structure and 121 00:05:52,320 --> 00:05:49,770 they tend to form in the super tidal 122 00:05:54,510 --> 00:05:52,330 environment that is the most landward 123 00:05:57,300 --> 00:05:54,520 and and most frequently exposed of 124 00:05:59,369 --> 00:05:57,310 coastal environments where evaporation 125 00:06:01,279 --> 00:05:59,379 causes precipitation of carbonate 126 00:06:04,139 --> 00:06:01,289 minerals and the pressure from that 127 00:06:06,959 --> 00:06:04,149 precipitation within pore waters causes 128 00:06:10,079 --> 00:06:06,969 beds to buckle so what we learn from 129 00:06:11,969 --> 00:06:10,089 this is first and foremost is that not 130 00:06:14,670 --> 00:06:11,979 only does the stacking of sedimentary 131 00:06:16,889 --> 00:06:14,680 rocks give us a record of time but 132 00:06:18,510 --> 00:06:16,899 physical and chemical features in those 133 00:06:20,730 --> 00:06:18,520 sedimentary rocks tell us something 134 00:06:22,740 --> 00:06:20,740 about environment so we actually have a 135 00:06:27,629 --> 00:06:22,750 time and space framework for thinking 136 00:06:30,629 --> 00:06:27,639 about life now if you took a piece of 137 00:06:31,889 --> 00:06:30,639 that carbonate and just put it made a 138 00:06:34,379 --> 00:06:31,899 thin section and put it under a 139 00:06:36,209 --> 00:06:34,389 microscope all you would see was 140 00:06:37,619 --> 00:06:36,219 interlocking crystals of dolomite not 141 00:06:39,540 --> 00:06:37,629 particularly interesting to the 142 00:06:40,950 --> 00:06:39,550 paleontological high 143 00:06:43,410 --> 00:06:40,960 but if you went to those black 144 00:06:46,740 --> 00:06:43,420 concretions that you see in there 145 00:06:49,500 --> 00:06:46,750 those consist of silica sio2 or chert 146 00:06:51,420 --> 00:06:49,510 which formed soon after the deposition 147 00:06:53,820 --> 00:06:51,430 of the parent carbonates and actually 148 00:06:56,280 --> 00:06:53,830 grew within the sediments at the expense 149 00:06:58,950 --> 00:06:56,290 of carbonates in a way that actually 150 00:07:01,920 --> 00:06:58,960 preserves micron scale textures of the 151 00:07:04,500 --> 00:07:01,930 original sediment so if you take those 152 00:07:06,720 --> 00:07:04,510 shirts make thin sections put them under 153 00:07:09,020 --> 00:07:06,730 the microscope what you will see is what 154 00:07:11,010 --> 00:07:09,030 you see in the bottom which are well 155 00:07:13,710 --> 00:07:11,020 morphologically preserved micro fossils 156 00:07:16,740 --> 00:07:13,720 each cell like unit there is about 4 157 00:07:20,400 --> 00:07:16,750 microns in diameter so the good news is 158 00:07:22,950 --> 00:07:20,410 that we actually have mechanisms in the 159 00:07:25,310 --> 00:07:22,960 Proterozoic Eon that preserve in an 160 00:07:28,560 --> 00:07:25,320 identifiable intractable state a 161 00:07:30,750 --> 00:07:28,570 microfossil record and indeed when you 162 00:07:33,710 --> 00:07:30,760 look across different environments in 163 00:07:36,390 --> 00:07:33,720 this package of sedimentary rocks from 164 00:07:38,820 --> 00:07:36,400 Spitsbergen not only in solicit 165 00:07:41,280 --> 00:07:38,830 carbonates but in fine-grained solicit 166 00:07:43,050 --> 00:07:41,290 clastic rocks that is to say shales we 167 00:07:46,170 --> 00:07:43,060 find a variety of things that on the 168 00:07:48,510 --> 00:07:46,180 right-hand side are very similar to 169 00:07:51,210 --> 00:07:48,520 living cyanobacteria and on the 170 00:07:53,310 --> 00:07:51,220 left-hand side we see things such as on 171 00:07:55,950 --> 00:07:53,320 the left where we have a fragment of a 172 00:07:58,950 --> 00:07:55,960 macroscopic structure that's in acidic 173 00:08:02,550 --> 00:07:58,960 in in organization very likely green 174 00:08:04,350 --> 00:08:02,560 algal we have 100 micron tests very 175 00:08:06,840 --> 00:08:04,360 similar to those of different kinds of 176 00:08:08,490 --> 00:08:06,850 tests date and maybe we find cysts like 177 00:08:11,790 --> 00:08:08,500 we see in the lower centre that are 178 00:08:15,120 --> 00:08:11,800 about 500 microns in diameter so there 179 00:08:18,420 --> 00:08:15,130 is a micro fossil record a more 180 00:08:20,310 --> 00:08:18,430 conspicuous record turns out to be the 181 00:08:23,640 --> 00:08:20,320 record of stromatolites that most of you 182 00:08:25,590 --> 00:08:23,650 are familiar with the lower-left is sort 183 00:08:27,720 --> 00:08:25,600 of the Mecca Mecca for Precambrian 184 00:08:30,690 --> 00:08:27,730 paleontology that's Shark Bay in Western 185 00:08:34,380 --> 00:08:30,700 Australia where again in the modern 186 00:08:37,470 --> 00:08:34,390 world we can actually see the processes 187 00:08:40,940 --> 00:08:37,480 by which microbial mat communities 188 00:08:44,790 --> 00:08:40,950 interact with sediments to produce these 189 00:08:46,530 --> 00:08:44,800 upwardly doming laminated structures and 190 00:08:49,670 --> 00:08:46,540 on the right you can see stromatolites 191 00:08:51,540 --> 00:08:49,680 that were nucleated on just blocks 192 00:08:53,460 --> 00:08:51,550 exactly the way the Shark Bay 193 00:08:55,740 --> 00:08:53,470 stromatolite SAR 194 00:08:58,920 --> 00:08:55,750 and then accreted by the trappin binding 195 00:09:00,420 --> 00:08:58,930 and precipitation of sediments the 196 00:09:02,670 --> 00:09:00,430 suppressed associated with microbial 197 00:09:05,280 --> 00:09:02,680 mats and as you see in the cliff behind 198 00:09:08,100 --> 00:09:05,290 that skier there you sometimes see 199 00:09:10,410 --> 00:09:08,110 structures that are several meters high 200 00:09:12,900 --> 00:09:10,420 and and tens of meters thick which are 201 00:09:14,850 --> 00:09:12,910 actually biomes or reefs which are 202 00:09:17,280 --> 00:09:14,860 constructed by these microbial 203 00:09:19,590 --> 00:09:17,290 communities so again there's a there's a 204 00:09:23,310 --> 00:09:19,600 macroscopic conspicuous and widespread 205 00:09:25,560 --> 00:09:23,320 record of benthic microbial communities 206 00:09:27,750 --> 00:09:25,570 preserved in these stromatolites and 207 00:09:30,420 --> 00:09:27,760 then of course as we've heard a little 208 00:09:32,220 --> 00:09:30,430 bit about earlier in the meeting and and 209 00:09:35,070 --> 00:09:32,230 most of you know there are at least 210 00:09:37,470 --> 00:09:35,080 several chemical ways in which life can 211 00:09:40,730 --> 00:09:37,480 impart a fingerprint to sedimentary 212 00:09:42,960 --> 00:09:40,740 rocks there is an isotopic fractionation 213 00:09:47,160 --> 00:09:42,970 associated with autotrophic carbon 214 00:09:49,620 --> 00:09:47,170 fixation so that if you look at in the 215 00:09:53,430 --> 00:09:49,630 Bahamas today the carbon isotopic 216 00:09:54,570 --> 00:09:53,440 composition of carbonates and compare 217 00:09:57,780 --> 00:09:54,580 that with the carbon isotopic 218 00:10:00,180 --> 00:09:57,790 composition of biologically produced 219 00:10:02,520 --> 00:10:00,190 organic matter that is sedimented with 220 00:10:06,000 --> 00:10:02,530 those carbonates they will differ by 221 00:10:08,790 --> 00:10:06,010 about 25 parts per thousand or per mil 222 00:10:11,100 --> 00:10:08,800 and broadly speaking that kind of 223 00:10:14,370 --> 00:10:11,110 fractionation pattern between carbonates 224 00:10:16,440 --> 00:10:14,380 and and organic matter really 225 00:10:18,780 --> 00:10:16,450 characterizes the known the known 226 00:10:21,780 --> 00:10:18,790 sedimentary record so we can start to 227 00:10:23,670 --> 00:10:21,790 interrogate the microbiological carbon 228 00:10:26,720 --> 00:10:23,680 cycle in the Proterozoic one can do the 229 00:10:30,600 --> 00:10:26,730 same thing for for sulfur as well and 230 00:10:34,950 --> 00:10:30,610 indeed under certain conditions there 231 00:10:36,630 --> 00:10:34,960 are molecular fossils preserved DNA and 232 00:10:39,870 --> 00:10:36,640 RNA are too good to eat so they 233 00:10:42,960 --> 00:10:39,880 basically are not found in in rocks of 234 00:10:45,720 --> 00:10:42,970 this age but lipids can actually 235 00:10:49,400 --> 00:10:45,730 preserve so we have things like stair 236 00:10:52,920 --> 00:10:49,410 Eanes the geologically stable forms of 237 00:10:55,980 --> 00:10:52,930 sterols hope annoyed z' derived from 238 00:10:58,380 --> 00:10:55,990 bacteria and independently of the 239 00:11:01,920 --> 00:10:58,390 morphological record these can enhance 240 00:11:05,520 --> 00:11:01,930 our sense of microbial physiology and 241 00:11:07,079 --> 00:11:05,530 diversities in the Proterozoic so in 242 00:11:09,509 --> 00:11:07,089 rocks that are 750 243 00:11:12,179 --> 00:11:09,519 million years old we see a fairly 244 00:11:15,179 --> 00:11:12,189 extensive record associated with 245 00:11:17,129 --> 00:11:15,189 sedimentary rocks that have textures 246 00:11:20,369 --> 00:11:17,139 that in general we understand from 247 00:11:22,290 --> 00:11:20,379 looking at modern analogs if we just for 248 00:11:24,860 --> 00:11:22,300 a moment double the age and go back to 249 00:11:27,420 --> 00:11:24,870 things that are 1500 million years old 250 00:11:29,970 --> 00:11:27,430 these are some rocks in the upper left 251 00:11:33,150 --> 00:11:29,980 from northern Siberia and basically 252 00:11:36,030 --> 00:11:33,160 everything I just said about 750 million 253 00:11:39,889 --> 00:11:36,040 year old rocks holds for these there are 254 00:11:42,540 --> 00:11:39,899 microphones those are 10 micron bars 255 00:11:44,759 --> 00:11:42,550 some of which are comparable to sign of 256 00:11:47,160 --> 00:11:44,769 bacteria others of which appear to be 257 00:11:49,290 --> 00:11:47,170 eukaryotic there are carbon and sulfur 258 00:11:52,590 --> 00:11:49,300 isotopic signatures there are molecular 259 00:11:54,869 --> 00:11:52,600 biomarkers and there are stromatolites I 260 00:11:57,629 --> 00:11:54,879 like this picture in the lower left for 261 00:11:59,999 --> 00:11:57,639 two reasons one is that my field partner 262 00:12:02,280 --> 00:12:00,009 here a man named Misha samokov is 263 00:12:04,259 --> 00:12:02,290 precisely 2 meters tall when he has his 264 00:12:05,970 --> 00:12:04,269 hat on so he's a great guy to have in 265 00:12:08,129 --> 00:12:05,980 the field so that you can get him as a 266 00:12:10,290 --> 00:12:08,139 scale for any picture that you make and 267 00:12:13,769 --> 00:12:10,300 you if you look at that picture you 268 00:12:15,720 --> 00:12:13,779 might say to yourself oh I see that 269 00:12:18,689 --> 00:12:15,730 little bun in the center of the picture 270 00:12:21,059 --> 00:12:18,699 is a microbial bio herb and you're 271 00:12:23,900 --> 00:12:21,069 exactly right that's a little reef maybe 272 00:12:26,280 --> 00:12:23,910 twice the side of size of this lectern 273 00:12:29,489 --> 00:12:26,290 but if you actually look at the surface 274 00:12:32,220 --> 00:12:29,499 on which Misha is standing it's it is a 275 00:12:34,290 --> 00:12:32,230 domed surface and it is part of a storm 276 00:12:37,470 --> 00:12:34,300 at oolitic biome that's probably about 277 00:12:40,949 --> 00:12:37,480 the size of this room and in fact the 278 00:12:43,350 --> 00:12:40,959 entire wall of rock behind Misha is part 279 00:12:45,600 --> 00:12:43,360 of a still larger biome that would be 280 00:12:47,400 --> 00:12:45,610 somewhat larger than this building so 281 00:12:49,769 --> 00:12:47,410 again we see that through the 282 00:12:52,819 --> 00:12:49,779 proterozoic eon microbial mat 283 00:12:56,400 --> 00:12:52,829 communities are largely surfacing 284 00:12:57,780 --> 00:12:56,410 environments from the the coastline all 285 00:13:00,660 --> 00:12:57,790 the way to the bottom of the photic zone 286 00:13:02,730 --> 00:13:00,670 and they can accrete structures that 287 00:13:07,590 --> 00:13:02,740 have dimensions equivalent to those of 288 00:13:09,239 --> 00:13:07,600 modern coral reefs now I'm not going to 289 00:13:12,079 --> 00:13:09,249 talk about the Archaean we've heard a 290 00:13:15,720 --> 00:13:12,089 lot about it except to say that this 291 00:13:18,619 --> 00:13:15,730 well-preserved record of life in 292 00:13:20,950 --> 00:13:18,629 Proterozoic rocks does provide us with 293 00:13:23,260 --> 00:13:20,960 something of a baseline 294 00:13:25,480 --> 00:13:23,270 that can help us to interpret the the 295 00:13:28,780 --> 00:13:25,490 deeper record so what you see here on 296 00:13:31,360 --> 00:13:28,790 the left are mr. Mehta likes that have 297 00:13:34,450 --> 00:13:31,370 been described by Abbie Elwood and 298 00:13:36,600 --> 00:13:34,460 others from the Pilbara region in 299 00:13:40,090 --> 00:13:36,610 Western Australia around 300 00:13:42,880 --> 00:13:40,100 2.3.4 excuse me billion years old and if 301 00:13:46,030 --> 00:13:42,890 you look at them the bottom half of the 302 00:13:48,910 --> 00:13:46,040 left-hand panel is very comforting you 303 00:13:50,560 --> 00:13:48,920 see these domed laminated structures 304 00:13:52,900 --> 00:13:50,570 that look much like the stromatolites 305 00:13:54,460 --> 00:13:52,910 we've just seen but it becomes a little 306 00:13:56,410 --> 00:13:54,470 more disconcerting when you continue 307 00:13:58,780 --> 00:13:56,420 upward and notice that the fabrics now 308 00:14:03,310 --> 00:13:58,790 become vertical what you're looking at 309 00:14:05,620 --> 00:14:03,320 are actually precipitated a sick euler 310 00:14:07,810 --> 00:14:05,630 aragonite crystals have precipitated on 311 00:14:11,290 --> 00:14:07,820 the sea floor this is an environment 312 00:14:14,350 --> 00:14:11,300 where carbonate was precipitating in 313 00:14:17,800 --> 00:14:14,360 remarkable fashion and we know from both 314 00:14:20,470 --> 00:14:17,810 today and proterozoic examples that when 315 00:14:23,590 --> 00:14:20,480 you have these high rates of carbonate 316 00:14:25,630 --> 00:14:23,600 precipitation you can make dough most 317 00:14:28,840 --> 00:14:25,640 laminated structures that are not 318 00:14:31,000 --> 00:14:28,850 templated by microbial mats so simply 319 00:14:33,430 --> 00:14:31,010 finding something that's Domo when the 320 00:14:35,590 --> 00:14:33,440 textures are precipitated is probably 321 00:14:37,270 --> 00:14:35,600 insufficient to declare victory and 322 00:14:39,070 --> 00:14:37,280 indeed when you look at the lower 323 00:14:40,240 --> 00:14:39,080 right-hand panel I mean that's but 324 00:14:43,180 --> 00:14:40,250 there's nothing that seems particularly 325 00:14:47,380 --> 00:14:43,190 biological about that is just a stacked 326 00:14:50,500 --> 00:14:47,390 set of precipitated carbonates on the 327 00:14:52,630 --> 00:14:50,510 other hand by looking at Proterozoic 328 00:14:54,750 --> 00:14:52,640 examples we find that if you go in and 329 00:14:58,060 --> 00:14:54,760 look microscopically at petrological 330 00:15:00,700 --> 00:14:58,070 textures you can sometimes find 331 00:15:03,940 --> 00:15:00,710 fingerprints of microbial mats and 332 00:15:07,540 --> 00:15:03,950 indeed when Abby and I and others looked 333 00:15:11,890 --> 00:15:07,550 at these in the in the these examples 334 00:15:14,290 --> 00:15:11,900 from the Pilbara we do see Petra logical 335 00:15:17,140 --> 00:15:14,300 evidence that there was at least a 336 00:15:19,030 --> 00:15:17,150 microbial influence on these but you 337 00:15:21,820 --> 00:15:19,040 really need to get at that level and 338 00:15:23,650 --> 00:15:21,830 that's a lesson from the Proterozoic how 339 00:15:25,810 --> 00:15:23,660 many at all have done similar things in 340 00:15:30,100 --> 00:15:25,820 rocks of comparable age from South 341 00:15:32,500 --> 00:15:30,110 Africa and indeed there's another thing 342 00:15:34,750 --> 00:15:32,510 that we can learn from the Proterozoic 343 00:15:37,110 --> 00:15:34,760 that can help us think about 344 00:15:40,829 --> 00:15:37,120 microstructures in the Archaean 345 00:15:43,180 --> 00:15:40,839 certainly the search image for 346 00:15:46,090 --> 00:15:43,190 exploration for microfossils in the 347 00:15:48,670 --> 00:15:46,100 Archaean comes from the success of 348 00:15:51,610 --> 00:15:48,680 finding microfossils incorporated in 349 00:15:53,620 --> 00:15:51,620 church in Proterozoic rocks on the other 350 00:15:55,990 --> 00:15:53,630 hand one thing we know from petrology 351 00:15:58,420 --> 00:15:56,000 and geochemistry is that many early 352 00:16:01,030 --> 00:15:58,430 Archaean shirts have been influenced by 353 00:16:04,120 --> 00:16:01,040 hydrothermal fluid flow and so we might 354 00:16:06,790 --> 00:16:04,130 want to ask is there an influence on the 355 00:16:09,400 --> 00:16:06,800 preserved textures of those rocks from 356 00:16:11,230 --> 00:16:09,410 hydrothermal activity and a way to 357 00:16:14,019 --> 00:16:11,240 evaluate that is to go into the 358 00:16:15,129 --> 00:16:14,029 Proterozoic where in general we have 359 00:16:18,370 --> 00:16:15,139 well-preserved 360 00:16:21,819 --> 00:16:18,380 fabrics and fossils and then look at 361 00:16:24,040 --> 00:16:21,829 local hydrothermal fluid flow and see 362 00:16:25,360 --> 00:16:24,050 what that does to the textures so what 363 00:16:29,650 --> 00:16:25,370 you're looking at in the lower right 364 00:16:33,400 --> 00:16:29,660 hand corner is a thin section of solicit 365 00:16:36,040 --> 00:16:33,410 I carbonate from some 740 million year 366 00:16:38,590 --> 00:16:36,050 old rocks in Canada if you look at the 367 00:16:40,840 --> 00:16:38,600 brown areas on the left and right they 368 00:16:44,259 --> 00:16:40,850 have textures which are very similar to 369 00:16:47,110 --> 00:16:44,269 those of early dye genetic charts in the 370 00:16:48,699 --> 00:16:47,120 Proterozoic in general but the white and 371 00:16:51,280 --> 00:16:48,709 purple areas that you see through the 372 00:16:53,769 --> 00:16:51,290 center of the slide are areas of 373 00:16:56,680 --> 00:16:53,779 concentrated hydrothermal fluid flow and 374 00:16:58,389 --> 00:16:56,690 within those all of the original 375 00:17:01,030 --> 00:16:58,399 textures of the church have been 376 00:17:04,270 --> 00:17:01,040 obliterated but as you see in the two 377 00:17:05,919 --> 00:17:04,280 panels of both that thin section that 378 00:17:09,159 --> 00:17:05,929 you both have the mobilization of 379 00:17:12,699 --> 00:17:09,169 organic mard matter and then it's it's 380 00:17:16,360 --> 00:17:12,709 recon dense ation forming 10 to 20 to 30 381 00:17:19,000 --> 00:17:16,370 micron steroidal micro structures now we 382 00:17:21,760 --> 00:17:19,010 know that there's fluid flow in the 383 00:17:25,630 --> 00:17:21,770 Archaean the upper panel on on the right 384 00:17:29,020 --> 00:17:25,640 shows organic matter condensing around a 385 00:17:31,480 --> 00:17:29,030 rhombohedral rhombohedral crystal and so 386 00:17:35,430 --> 00:17:31,490 we know that happens so the question is 387 00:17:38,320 --> 00:17:35,440 can we then make a judgment about 388 00:17:41,490 --> 00:17:38,330 whether what we're looking at in these 389 00:17:44,700 --> 00:17:41,500 very old roxas is associated with 390 00:17:48,140 --> 00:17:44,710 hydrothermal activity or maybe 391 00:17:50,030 --> 00:17:48,150 excitingly true biological remains and 392 00:17:51,620 --> 00:17:50,040 and I'm not saying that all things that 393 00:17:54,860 --> 00:17:51,630 have been reported as fossils in the 394 00:17:57,980 --> 00:17:54,870 Archaean are other than that it's just 395 00:18:00,049 --> 00:17:57,990 that there's probably one more loop we 396 00:18:03,770 --> 00:18:00,059 need to go through to have confidence 397 00:18:07,490 --> 00:18:03,780 and this is where that preservation of 398 00:18:08,690 --> 00:18:07,500 textures comes the the expectation at 399 00:18:12,350 --> 00:18:08,700 least for the work that we and others 400 00:18:14,510 --> 00:18:12,360 have done on hydrothermal alteration in 401 00:18:17,510 --> 00:18:14,520 the Proterozoic is that it will tend to 402 00:18:20,480 --> 00:18:17,520 obliterate textures so if on the Left 403 00:18:22,070 --> 00:18:20,490 where we're looking at rocks that are a 404 00:18:26,799 --> 00:18:22,080 little more than three billion years old 405 00:18:29,870 --> 00:18:26,809 from South Africa if you have preserved 406 00:18:31,790 --> 00:18:29,880 textures on a coarser scale and what 407 00:18:34,549 --> 00:18:31,800 you're looking at there is simply a 408 00:18:38,270 --> 00:18:34,559 shard of some laminated possibly matte 409 00:18:41,150 --> 00:18:38,280 material that actually contains eight to 410 00:18:43,490 --> 00:18:41,160 ten microns spheroids again I don't know 411 00:18:45,560 --> 00:18:43,500 that these are unequivocally fossils but 412 00:18:48,580 --> 00:18:45,570 at least they are in the context of 413 00:18:51,650 --> 00:18:48,590 preserved texture so again I think that 414 00:18:54,049 --> 00:18:51,660 the experience with better preserved 415 00:18:56,750 --> 00:18:54,059 materials in the Proterozoic can at 416 00:18:58,610 --> 00:18:56,760 least help us as we evaluate this 417 00:19:01,820 --> 00:18:58,620 precious but limited record of the 418 00:19:07,100 --> 00:19:01,830 Archaean now just a few words about 419 00:19:09,740 --> 00:19:07,110 cyanobacteria in the Proterozoic many of 420 00:19:12,020 --> 00:19:09,750 the sign and bacteria like fossils found 421 00:19:15,530 --> 00:19:12,030 in Proterozoic rocks seem to be 422 00:19:18,049 --> 00:19:15,540 generally similar to living sign of 423 00:19:20,360 --> 00:19:18,059 bacteria there are some populations that 424 00:19:23,299 --> 00:19:20,370 are very specifically similar so if you 425 00:19:25,700 --> 00:19:23,309 went to the Bahamas today and looked at 426 00:19:28,730 --> 00:19:25,710 who is these little concentric carbonate 427 00:19:31,520 --> 00:19:28,740 balls that accumulate in the in the 428 00:19:33,880 --> 00:19:31,530 tidal zone you would find that as we see 429 00:19:37,970 --> 00:19:33,890 in the lower right there they are 430 00:19:39,980 --> 00:19:37,980 festooned with endo lithic or boring 431 00:19:42,770 --> 00:19:39,990 sign a bacteria that basically burrow 432 00:19:46,669 --> 00:19:42,780 into them and live beneath the surface 433 00:19:48,950 --> 00:19:46,679 of the hood they are diverse they have 434 00:19:50,870 --> 00:19:48,960 for sign of bacteria rather complex 435 00:19:52,820 --> 00:19:50,880 developmental patterns they show 436 00:19:56,120 --> 00:19:52,830 evidence of behavior in the sense that 437 00:19:58,840 --> 00:19:56,130 today we can see things wrote down into 438 00:20:01,310 --> 00:19:58,850 the wood until they reach a point of 439 00:20:02,419 --> 00:20:01,320 light limitation and then they grow back 440 00:20:05,840 --> 00:20:02,429 up again we see 441 00:20:07,399 --> 00:20:05,850 same thing in the Proterozoic what we're 442 00:20:10,190 --> 00:20:07,409 looking at in the upper left is simply 443 00:20:12,980 --> 00:20:10,200 cross bedded who is there's a solicit I 444 00:20:15,259 --> 00:20:12,990 do it in the lower left and you can see 445 00:20:17,899 --> 00:20:15,269 that all around the surface it has these 446 00:20:20,450 --> 00:20:17,909 n dualistic structures one of which 447 00:20:22,609 --> 00:20:20,460 about a millimeter long from end to end 448 00:20:26,529 --> 00:20:22,619 is seen in the upper right and in this 449 00:20:29,299 --> 00:20:26,539 case we actually have several 450 00:20:31,700 --> 00:20:29,309 populations that are essentially 451 00:20:35,180 --> 00:20:31,710 indistinguishable from modern 452 00:20:39,350 --> 00:20:35,190 populations found in in who is today and 453 00:20:41,480 --> 00:20:39,360 so that we think this gives us a rare 454 00:20:44,090 --> 00:20:41,490 calibration point for looking at 455 00:20:46,730 --> 00:20:44,100 molecular clocks for example inside a 456 00:20:48,259 --> 00:20:46,740 bacteria and then there are these things 457 00:20:50,899 --> 00:20:48,269 in the upper right one thing that we 458 00:20:52,700 --> 00:20:50,909 find in rocks beginning around 1600 459 00:20:55,730 --> 00:20:52,710 million years ago are these sort of 460 00:20:58,519 --> 00:20:55,740 elongate cigar like structures that 461 00:21:02,779 --> 00:20:58,529 would be about 60 microns long they are 462 00:21:04,940 --> 00:21:02,789 very similar to the akan eats of gnostic 463 00:21:06,799 --> 00:21:04,950 alien sign of bacteria which some of you 464 00:21:09,049 --> 00:21:06,809 will know is the one clade of sign of 465 00:21:12,139 --> 00:21:09,059 bacteria that differentiates different 466 00:21:15,739 --> 00:21:12,149 cell types it has been suggested that 467 00:21:18,379 --> 00:21:15,749 maybe these are something else but one 468 00:21:21,350 --> 00:21:18,389 of the things that I think helps us to 469 00:21:23,690 --> 00:21:21,360 interpret these structures as achenes 470 00:21:26,299 --> 00:21:23,700 therefore again providing a calibration 471 00:21:29,389 --> 00:21:26,309 point for sign of bacterial evolution is 472 00:21:31,820 --> 00:21:29,399 that they are uniquely associated with 473 00:21:34,909 --> 00:21:31,830 very short cellular trichomes whose 474 00:21:36,950 --> 00:21:34,919 dimensions are precisely those of these 475 00:21:44,239 --> 00:21:36,960 achenes like structures that they're 476 00:21:46,940 --> 00:21:44,249 found among the the in the modern day 477 00:21:49,369 --> 00:21:46,950 when akka NEETs germinate they they form 478 00:21:52,159 --> 00:21:49,379 things called germ Ling's which are very 479 00:21:54,470 --> 00:21:52,169 short trichomes indistinguishable from 480 00:21:56,389 --> 00:21:54,480 these so again I think this tells us 481 00:22:00,109 --> 00:21:56,399 that by sixteen hundred million years 482 00:22:02,659 --> 00:22:00,119 ago we have gotten to the point of sign 483 00:22:04,220 --> 00:22:02,669 of bacterial diversification where we 484 00:22:07,310 --> 00:22:04,230 have those sign of bacteria that 485 00:22:09,200 --> 00:22:07,320 differentiate cell types there have been 486 00:22:11,930 --> 00:22:09,210 a number of sign of bacterial phylogeny 487 00:22:15,109 --> 00:22:11,940 x' published over the years this is just 488 00:22:15,620 --> 00:22:15,119 one from Betty sure Meister at Al what 489 00:22:18,500 --> 00:22:15,630 this 490 00:22:21,620 --> 00:22:18,510 jess is that the Proterozoic was a time 491 00:22:25,630 --> 00:22:21,630 when sign of bacterial diversity was 492 00:22:28,130 --> 00:22:25,640 unfolding and indeed I think that's very 493 00:22:31,700 --> 00:22:28,140 similar to the story we get from the 494 00:22:34,480 --> 00:22:31,710 fossil record in general moving then to 495 00:22:37,790 --> 00:22:34,490 eukaryotes again as all of you know 496 00:22:39,320 --> 00:22:37,800 eukaryotes are both genetically and and 497 00:22:42,860 --> 00:22:39,330 silent so they are structurally 498 00:22:45,980 --> 00:22:42,870 different from prokaryotes and so the 499 00:22:49,520 --> 00:22:45,990 question is can we actually document a 500 00:22:51,380 --> 00:22:49,530 record of eukaryotic evolution back 501 00:22:55,850 --> 00:22:51,390 through the Proterozoic to complement 502 00:22:58,100 --> 00:22:55,860 that of a bacteria and again the first 503 00:23:00,230 --> 00:22:58,110 question is practical that is when we 504 00:23:02,630 --> 00:23:00,240 find a micro fossil how can we tell 505 00:23:04,730 --> 00:23:02,640 whether it's eukaryotic it doesn't have 506 00:23:06,950 --> 00:23:04,740 a membrane bounded nucleus it doesn't 507 00:23:09,980 --> 00:23:06,960 have multiple linear chromosomes it 508 00:23:12,590 --> 00:23:09,990 doesn't have small subunit ribosomal RNA 509 00:23:17,330 --> 00:23:12,600 or any of these things all that 510 00:23:18,830 --> 00:23:17,340 preserves for the most part are walls so 511 00:23:20,060 --> 00:23:18,840 if you're a eukaryote that didn't make a 512 00:23:22,640 --> 00:23:20,070 cell wall if there's a fair chance 513 00:23:24,320 --> 00:23:22,650 you're only possibility of anything in 514 00:23:27,770 --> 00:23:24,330 the geologic record would be as a 515 00:23:29,660 --> 00:23:27,780 molecular staring microfossil so here's 516 00:23:33,050 --> 00:23:29,670 one example something called Shu useful 517 00:23:36,500 --> 00:23:33,060 idiom from 14 to 16 hundred million year 518 00:23:37,940 --> 00:23:36,510 old rocks in in China it's large about 519 00:23:40,340 --> 00:23:37,950 150 microns 520 00:23:42,380 --> 00:23:40,350 well that might prejudice you toward a 521 00:23:44,900 --> 00:23:42,390 eukaryotic interpretation it's not by 522 00:23:47,480 --> 00:23:44,910 itself definitive on the other hand 523 00:23:50,720 --> 00:23:47,490 these are festooned with regularly 524 00:23:53,030 --> 00:23:50,730 distributed processes and if you look at 525 00:23:56,120 --> 00:23:53,040 the cell wall particularly in the SEM in 526 00:23:58,490 --> 00:23:56,130 the lower right it basically consists of 527 00:24:02,570 --> 00:23:58,500 these tessellated plates and when you 528 00:24:05,960 --> 00:24:02,580 look at it in TEM work done by m9y el 529 00:24:09,620 --> 00:24:05,970 chavo here you can see a complexity of 530 00:24:12,140 --> 00:24:09,630 wall structure which is very similar to 531 00:24:17,030 --> 00:24:12,150 the complexity we see in eukaryotic 532 00:24:19,280 --> 00:24:17,040 cells very different from the micro 533 00:24:21,620 --> 00:24:19,290 structure that we would see and say sign 534 00:24:26,660 --> 00:24:21,630 of bacterial envelopes so I think 535 00:24:28,490 --> 00:24:26,670 together size wall complexity and and 536 00:24:29,480 --> 00:24:28,500 morphology tell us that this was a 537 00:24:32,330 --> 00:24:29,490 eukaryotic 538 00:24:34,280 --> 00:24:32,340 sell and just to quote Tom 539 00:24:36,590 --> 00:24:34,290 cavalier-smith a prominent protest 540 00:24:38,480 --> 00:24:36,600 ologists it says sis with spines 541 00:24:40,640 --> 00:24:38,490 articulate surface sculpturing would 542 00:24:43,130 --> 00:24:40,650 probably have required both an ending 543 00:24:45,049 --> 00:24:43,140 endomembrane system and a cytoskeleton 544 00:24:47,540 --> 00:24:45,059 the most fundamental features of the 545 00:24:50,030 --> 00:24:47,550 eukaryotic cell and I think that's right 546 00:24:52,880 --> 00:24:50,040 and that gives us confidence that a that 547 00:24:55,880 --> 00:24:52,890 we're looking at a eukaryote and also 548 00:24:58,430 --> 00:24:55,890 that preservable features of eukaryotes 549 00:25:01,130 --> 00:24:58,440 can actually allow us to make some 550 00:25:03,140 --> 00:25:01,140 inferences about features of cell 551 00:25:05,330 --> 00:25:03,150 biology that are not well preserved 552 00:25:08,419 --> 00:25:05,340 again that particular fossil is over 553 00:25:11,120 --> 00:25:08,429 fourteen hundred million years old now 554 00:25:13,490 --> 00:25:11,130 I'm gonna skip through the next thing 555 00:25:17,299 --> 00:25:13,500 because I already hear the hoofbeats of 556 00:25:20,150 --> 00:25:17,309 the end of time coming up I did want to 557 00:25:22,040 --> 00:25:20,160 say that with Emmanuel we've published a 558 00:25:23,750 --> 00:25:22,050 paper on some fourteen to fifteen 559 00:25:27,650 --> 00:25:23,760 hundred million year old rocks from 560 00:25:29,720 --> 00:25:27,660 northern Australia and these are have a 561 00:25:31,940 --> 00:25:29,730 moderate diversity of things that we 562 00:25:38,630 --> 00:25:31,950 think are eukaryotic they are not easy 563 00:25:40,549 --> 00:25:38,640 to place follow genetically but because 564 00:25:42,950 --> 00:25:40,559 of some of the forms we think we can 565 00:25:45,380 --> 00:25:42,960 identify some of them as being hospital 566 00:25:49,100 --> 00:25:45,390 for example as opposed to photosynthetic 567 00:25:51,320 --> 00:25:49,110 we know that we can see evidence of cell 568 00:25:53,270 --> 00:25:51,330 differentiation I think people sometimes 569 00:25:55,070 --> 00:25:53,280 think that cell differentiation is the 570 00:25:58,070 --> 00:25:55,080 special province of multicellular 571 00:25:59,750 --> 00:25:58,080 organisms but most eukaryotic organisms 572 00:26:02,560 --> 00:25:59,760 differentiate different cells during 573 00:26:06,640 --> 00:26:02,570 their life cycle and we do see cysts 574 00:26:09,040 --> 00:26:06,650 just zip through that we start seeing 575 00:26:10,880 --> 00:26:09,050 through the work of Nick Butterfield 576 00:26:13,820 --> 00:26:10,890 things that we can actually identify 577 00:26:16,250 --> 00:26:13,830 follow genetically by about ten hundred 578 00:26:20,330 --> 00:26:16,260 and fifty million years ago these I 579 00:26:22,760 --> 00:26:20,340 think are well interpreted as a red 580 00:26:25,490 --> 00:26:22,770 algae which tell us that not only have 581 00:26:27,560 --> 00:26:25,500 brown groups come into existence within 582 00:26:29,480 --> 00:26:27,570 the eukaryotes at this time but 583 00:26:34,100 --> 00:26:29,490 photosynthesis has come to them simple 584 00:26:38,169 --> 00:26:34,110 multicellularity has come to them they 585 00:26:41,270 --> 00:26:38,179 just keep going through this 586 00:26:45,500 --> 00:26:41,280 interestingly although we have a record 587 00:26:51,860 --> 00:26:48,430 at least sixteen hundred million years 588 00:26:55,100 --> 00:26:51,870 when we look at the biomarker record 589 00:26:56,900 --> 00:26:55,110 here from the work of yep and brock's we 590 00:27:01,870 --> 00:26:56,910 find that there's not much record of 591 00:27:06,110 --> 00:27:01,880 eukaryotic sin the form of of lipid 592 00:27:09,260 --> 00:27:06,120 biomarkers indeed again from this mezzo 593 00:27:11,570 --> 00:27:09,270 protein or middle Proterozoic basin we 594 00:27:14,299 --> 00:27:11,580 have evidence that most of the primary 595 00:27:15,890 --> 00:27:14,309 production was bacterial and indeed in 596 00:27:18,650 --> 00:27:15,900 this particular basin at this particular 597 00:27:22,280 --> 00:27:18,660 time the lower part of the photic zone 598 00:27:25,520 --> 00:27:22,290 was an toxic because we see biomarkers 599 00:27:27,220 --> 00:27:25,530 that are made by green and purple sulfur 600 00:27:31,640 --> 00:27:27,230 bacteria 601 00:27:33,980 --> 00:27:31,650 now although eukaryotes originated early 602 00:27:36,500 --> 00:27:33,990 about eight hundred million years ago we 603 00:27:39,680 --> 00:27:36,510 see a major diversification with new 604 00:27:42,710 --> 00:27:39,690 types of fossils like these vase shape 605 00:27:45,590 --> 00:27:42,720 tests we start seeing scales of the type 606 00:27:48,350 --> 00:27:45,600 that so you might associate with a 607 00:27:50,200 --> 00:27:48,360 couple of the four heads today we see an 608 00:27:54,200 --> 00:27:50,210 increase in the diversity of 609 00:27:56,090 --> 00:27:54,210 multicellular and seen acidic types we 610 00:27:59,230 --> 00:27:56,100 see an increase in the diversity of 611 00:28:03,080 --> 00:27:59,240 cysts and other types and one might ask 612 00:28:06,350 --> 00:28:03,090 why halfway through the history of 613 00:28:09,799 --> 00:28:06,360 eukaryotes do we see this difference and 614 00:28:11,690 --> 00:28:09,809 let me suggest an ecological argument 615 00:28:14,600 --> 00:28:11,700 and you can take this for what it's what 616 00:28:17,150 --> 00:28:14,610 it's worth but many people think that 617 00:28:19,490 --> 00:28:17,160 there's at least an ecological component 618 00:28:21,620 --> 00:28:19,500 to the driving of diversification of 619 00:28:26,450 --> 00:28:21,630 animals in the Cambrian that is 620 00:28:29,720 --> 00:28:26,460 associated with carnivorous and so if 621 00:28:33,260 --> 00:28:29,730 there were a significant uptick in the 622 00:28:35,360 --> 00:28:33,270 ecological importance of protists in 623 00:28:38,990 --> 00:28:35,370 eukaryotes that eat other eukaryotes 624 00:28:44,240 --> 00:28:39,000 that might drive much of what we see in 625 00:28:47,000 --> 00:28:44,250 the in in the neoproterozoic and indeed 626 00:28:49,250 --> 00:28:47,010 when you do a sort of character analysis 627 00:28:50,930 --> 00:28:49,260 with phylogeny x' it's pretty clear that 628 00:28:53,419 --> 00:28:50,940 eukaryotes that make their living 629 00:28:55,940 --> 00:28:53,429 largely by eating other eukaryotes fika 630 00:28:58,549 --> 00:28:55,950 trophic lis are derived groups of 631 00:29:00,350 --> 00:28:58,559 alekhya ler clock ages suggest an origin 632 00:29:04,340 --> 00:29:00,360 around at least in the neoproterozoic 633 00:29:06,259 --> 00:29:04,350 and certainly fossils these vase shape 634 00:29:09,310 --> 00:29:06,269 fossils which are abundant in rocks 635 00:29:12,620 --> 00:29:09,320 beginning around 750 million years ago 636 00:29:14,960 --> 00:29:12,630 clearly made by things like test date 637 00:29:17,899 --> 00:29:14,970 and maybe today some of their modern 638 00:29:21,560 --> 00:29:17,909 relatives are in fact eukaryote eaters 639 00:29:24,110 --> 00:29:21,570 and one can guess a that the reason you 640 00:29:26,899 --> 00:29:24,120 have a test is for protection and B 641 00:29:30,500 --> 00:29:26,909 there's actually evidence of predation 642 00:29:32,539 --> 00:29:30,510 on these things also we find beginning 643 00:29:35,930 --> 00:29:32,549 in rocks of this age that we start 644 00:29:39,470 --> 00:29:35,940 seeing scales indeed these scales 645 00:29:41,810 --> 00:29:39,480 described by Phoebe Cohen are probably 646 00:29:46,789 --> 00:29:41,820 the most diverse eukaryotic fossils 647 00:29:49,460 --> 00:29:46,799 before animals and again while we can't 648 00:29:51,919 --> 00:29:49,470 pin them down follow genetically there 649 00:29:54,950 --> 00:29:51,929 is reason to think that they might serve 650 00:29:58,009 --> 00:29:54,960 the the role of protection against other 651 00:30:00,159 --> 00:29:58,019 protists and then finally one can think 652 00:30:03,200 --> 00:30:00,169 of multicellularity as a defense and 653 00:30:05,990 --> 00:30:03,210 just to argue this one more point that 654 00:30:08,810 --> 00:30:06,000 I'll finish there's a wonderful paper 655 00:30:12,680 --> 00:30:08,820 some years ago in which people had were 656 00:30:13,820 --> 00:30:12,690 growing single-celled algae in culture 657 00:30:15,049 --> 00:30:13,830 you can grow these for a million 658 00:30:18,350 --> 00:30:15,059 generation they're always be 659 00:30:21,230 --> 00:30:18,360 single-celled you put in a eukaryotic 660 00:30:23,299 --> 00:30:21,240 predator and within 10 to 20 generations 661 00:30:25,070 --> 00:30:23,309 they're obligate Lea multicellular and 662 00:30:27,080 --> 00:30:25,080 they will stay multicellular even if you 663 00:30:30,440 --> 00:30:27,090 remove the predator and the reason for 664 00:30:32,840 --> 00:30:30,450 that is that when you stay attached 665 00:30:36,500 --> 00:30:32,850 after cell division you can't get eaten 666 00:30:38,480 --> 00:30:36,510 so there may be something that since 667 00:30:40,940 --> 00:30:38,490 molecular clocks suggest that animals 668 00:30:42,950 --> 00:30:40,950 are taking shape on this timescale maybe 669 00:30:46,100 --> 00:30:42,960 that has something to do with it last 670 00:30:49,159 --> 00:30:46,110 point there's a conundrum here in that 671 00:30:51,710 --> 00:30:49,169 we think that eukaryotes existed early 672 00:30:54,529 --> 00:30:51,720 we have evidence that photosynthesis 673 00:30:57,169 --> 00:30:54,539 came to eukaryotes fairly early yet if 674 00:30:59,810 --> 00:30:57,179 you look at the biomarker record it 675 00:31:03,379 --> 00:30:59,820 looks like eukaryotes are only becoming 676 00:31:06,590 --> 00:31:03,389 important in the phytoplankton about 700 677 00:31:09,440 --> 00:31:06,600 and about 700 million years ago and 678 00:31:09,800 --> 00:31:09,450 again I think ecological modeling can 679 00:31:12,230 --> 00:31:09,810 help 680 00:31:16,780 --> 00:31:12,240 on the right is an interesting diagram 681 00:31:20,120 --> 00:31:16,790 and what it shows is that if you look at 682 00:31:22,250 --> 00:31:20,130 basically population size which is what 683 00:31:27,410 --> 00:31:22,260 we're really looking at on the x-axis 684 00:31:31,130 --> 00:31:27,420 and just look at the arms right size is 685 00:31:33,020 --> 00:31:31,140 on the x-axis and population numbers on 686 00:31:36,130 --> 00:31:33,030 on there sorry 687 00:31:39,890 --> 00:31:36,140 body size on the left on the y-axis 688 00:31:44,180 --> 00:31:39,900 numbers on on the on the right at low 689 00:31:47,750 --> 00:31:44,190 nutrient levels small cells always win 690 00:31:49,370 --> 00:31:47,760 and so today in the lowest nutrient 691 00:31:51,830 --> 00:31:49,380 levels of the oceans sign of bacteria 692 00:31:53,870 --> 00:31:51,840 dominate primary production and it may 693 00:31:56,390 --> 00:31:53,880 well be that the reason sign of bacteria 694 00:31:58,640 --> 00:31:56,400 dominate primary production in through 695 00:32:01,820 --> 00:31:58,650 most of the Proterozoic is that nutrient 696 00:32:03,440 --> 00:32:01,830 levels are very low independently of any 697 00:32:05,980 --> 00:32:03,450 paleontological evidence there's a 698 00:32:08,750 --> 00:32:05,990 evidence for a change in phosphate 699 00:32:11,500 --> 00:32:08,760 availability beginning in the later in 700 00:32:14,750 --> 00:32:11,510 the Oh Proterozoic and what will happen 701 00:32:16,760 --> 00:32:14,760 ecologically if you add nutrients you 702 00:32:19,340 --> 00:32:16,770 increase the population size of the sign 703 00:32:21,770 --> 00:32:19,350 of bacteria but only to the point where 704 00:32:25,370 --> 00:32:21,780 they become controlled by grazers and at 705 00:32:30,220 --> 00:32:25,380 that point larger size classes can grow 706 00:32:32,930 --> 00:32:30,230 in so it may be that the reason that 707 00:32:34,750 --> 00:32:32,940 eukaryotic algae become important only 708 00:32:39,200 --> 00:32:34,760 toward the end of the Proterozoic is 709 00:32:41,030 --> 00:32:39,210 that nutrient status is changing in in 710 00:32:45,200 --> 00:32:41,040 the oceans and that has a further 711 00:32:48,650 --> 00:32:45,210 consequence because once you replace or 712 00:32:51,020 --> 00:32:48,660 add larger cells at the base of the food 713 00:32:53,390 --> 00:32:51,030 chain to the smaller ones you end up 714 00:32:55,910 --> 00:32:53,400 distributing more energy and biomass 715 00:32:58,010 --> 00:32:55,920 higher in the food web so it may be 716 00:33:01,880 --> 00:32:58,020 there at least one component of the 717 00:33:06,080 --> 00:33:01,890 riddle for why animals radiate when they 718 00:33:08,330 --> 00:33:06,090 do is that the changing nature of the 719 00:33:12,010 --> 00:33:08,340 primary producers in ecosystems is 720 00:33:15,330 --> 00:33:12,020 actually making more energy and biomass 721 00:33:18,269 --> 00:33:15,340 available for larger organisms of 722 00:33:22,680 --> 00:33:18,279 of food webs so with that then let me 723 00:33:24,899 --> 00:33:22,690 just end punchlines life and environment 724 00:33:28,169 --> 00:33:24,909 are recorded over a four billion year 725 00:33:29,759 --> 00:33:28,179 history of the earth and that they seem 726 00:33:33,330 --> 00:33:29,769 to be closely intertwined throughout 727 00:33:34,919 --> 00:33:33,340 that history the Proterozoic is a world 728 00:33:36,629 --> 00:33:34,929 that is both biologically an 729 00:33:40,320 --> 00:33:36,639 environmentally distinct from what 730 00:33:44,129 --> 00:33:40,330 became for and after and importantly 731 00:33:46,499 --> 00:33:44,139 that Proterozoic rocks provide maybe our 732 00:33:49,409 --> 00:33:46,509 best template for thinking about how to 733 00:33:52,230 --> 00:33:49,419 interpret the deeper rock record and 734 00:33:53,970 --> 00:33:52,240 also provide a guide for the exploration 735 00:34:00,659 --> 00:33:53,980 of sedimentary rocks on Mars and 736 00:34:08,159 --> 00:34:00,669 elsewhere so thank you very much thank 737 00:34:11,030 --> 00:34:08,169 you very much for a beautiful talk in 738 00:34:13,710 --> 00:34:11,040 the final resort there are quite a few 739 00:34:16,169 --> 00:34:13,720 mass extinctions and I'm wondering 740 00:34:18,149 --> 00:34:16,179 during the 2000 million years of the 741 00:34:19,169 --> 00:34:18,159 Proterozoic weather there's if are there 742 00:34:21,319 --> 00:34:19,179 any sediment layers that are 743 00:34:23,280 --> 00:34:21,329 well-preserved enough and nor 744 00:34:25,230 --> 00:34:23,290 chronologically ordered that you can 745 00:34:32,309 --> 00:34:25,240 test or try to see if there were any 746 00:34:35,129 --> 00:34:32,319 mass extinctions there's at least one 747 00:34:37,859 --> 00:34:35,139 case we can make we people talked 748 00:34:40,559 --> 00:34:37,869 yesterday about these global glaciation 749 00:34:43,099 --> 00:34:40,569 something called snowball Earth's one 750 00:34:48,540 --> 00:34:43,109 that begins actually rather precisely at 751 00:34:50,190 --> 00:34:48,550 716 million years ago ends about 660 752 00:34:53,399 --> 00:34:50,200 million years ago and then a second 753 00:34:56,700 --> 00:34:53,409 shorter lived one that ends 635 million 754 00:35:01,319 --> 00:34:56,710 years ago if you look at the nature of 755 00:35:04,130 --> 00:35:01,329 the eukaryotic biota before the earlier 756 00:35:08,069 --> 00:35:04,140 of those ice ages you have this 757 00:35:10,400 --> 00:35:08,079 relatively rich diversity of a variety 758 00:35:14,880 --> 00:35:10,410 of eukaryotic clades 759 00:35:17,430 --> 00:35:14,890 very few of which actually make it 760 00:35:20,130 --> 00:35:17,440 through the glaciations now we know that 761 00:35:23,040 --> 00:35:20,140 some eukaryotic clades did because 762 00:35:25,349 --> 00:35:23,050 there's reason to believe that some of 763 00:35:27,350 --> 00:35:25,359 the diversity that radiates after the 764 00:35:29,120 --> 00:35:27,360 ice ages has its roots 765 00:35:31,580 --> 00:35:29,130 in this earlier diversification of 766 00:35:34,070 --> 00:35:31,590 eukaryotes but at the species and genus 767 00:35:36,350 --> 00:35:34,080 level not much makes it through those 768 00:35:40,730 --> 00:35:36,360 ice ages so that's our that's our our 769 00:35:42,950 --> 00:35:40,740 one best look at mass extinction now for 770 00:35:45,320 --> 00:35:42,960 prokaryotes bacteria it's it's a little 771 00:35:46,910 --> 00:35:45,330 bit different in that those tell my 772 00:35:49,640 --> 00:35:46,920 students you can brush your teeth in the 773 00:35:52,970 --> 00:35:49,650 morning and kill 99% of the bacteria in 774 00:35:55,520 --> 00:35:52,980 your mouth but by evening your teeth 775 00:35:56,810 --> 00:35:55,530 will be filmed again so it's it's I 776 00:36:00,640 --> 00:35:56,820 think it's a it's a it's a different 777 00:36:02,930 --> 00:36:00,650 order of exercise to try and drive 778 00:36:05,390 --> 00:36:02,940 bacteria to extinction and we certainly 779 00:36:08,540 --> 00:36:05,400 see no evidence of it so when people say 780 00:36:10,370 --> 00:36:08,550 that the Permian Triassic extinction was 781 00:36:11,750 --> 00:36:10,380 the largest ever that's probably not 782 00:36:14,960 --> 00:36:11,760 true because of the one you just 783 00:36:18,080 --> 00:36:14,970 described well you know it's very hard 784 00:36:20,360 --> 00:36:18,090 to quantify what's going going on so how 785 00:36:22,010 --> 00:36:20,370 I sometimes write about the remote 786 00:36:24,260 --> 00:36:22,020 Triassic and I need to be able to say 787 00:36:27,050 --> 00:36:24,270 it's the largest mass extinction ever so 788 00:36:37,130 --> 00:36:27,060 I'll stick to that story the extent to 789 00:36:46,240 --> 00:36:37,140 which is true we simply don't know any 790 00:36:51,140 --> 00:36:48,590 how much of this shift from 791 00:36:53,900 --> 00:36:51,150 cyanobacteria to eukaryotic algae could 792 00:36:56,510 --> 00:36:53,910 be a result of increased availability of 793 00:36:59,270 --> 00:36:56,520 fixed nitrogen well I guess one of the 794 00:37:01,940 --> 00:36:59,280 questions is it could be important in an 795 00:37:05,140 --> 00:37:01,950 area and I wrote about this some years 796 00:37:07,670 --> 00:37:05,150 ago in in some ways I think that 797 00:37:10,490 --> 00:37:07,680 nitrogen nitrogen may prove to be a 798 00:37:12,890 --> 00:37:10,500 responder here I mean there is evidence 799 00:37:16,070 --> 00:37:12,900 based on nitrogen isotopes that at least 800 00:37:18,500 --> 00:37:16,080 in shallow water environments there was 801 00:37:22,160 --> 00:37:18,510 some nitrate available as you go 802 00:37:24,700 --> 00:37:22,170 offshore nitrogen isotopes indicate a 803 00:37:27,410 --> 00:37:24,710 greater role for nitrogen fixation and 804 00:37:28,450 --> 00:37:27,420 certainly one of the things I didn't 805 00:37:32,270 --> 00:37:28,460 have time to talk about but 806 00:37:35,420 --> 00:37:32,280 environmentally in literally every 807 00:37:40,010 --> 00:37:35,430 Proterozoic Basin but one within the 808 00:37:42,440 --> 00:37:40,020 range of of basin depths recorded in 809 00:37:44,450 --> 00:37:42,450 sedimentary basins which is really only 810 00:37:47,990 --> 00:37:44,460 you know a couple hundred meters at best 811 00:37:52,400 --> 00:37:48,000 you capture the transition from object' 812 00:37:54,650 --> 00:37:52,410 anoxic water masses so most of the 813 00:37:58,030 --> 00:37:54,660 Proterozoic appears to be this fairly 814 00:38:02,360 --> 00:37:58,040 thin veneer probably tens of meters of 815 00:38:04,040 --> 00:38:02,370 oxic waters beneath an anoxic oxygen 816 00:38:06,320 --> 00:38:04,050 minimum zone and there's no question 817 00:38:08,810 --> 00:38:06,330 that that's a perfect conditions for 818 00:38:12,320 --> 00:38:08,820 actually destroying nitrogen and we get 819 00:38:15,620 --> 00:38:12,330 back to the environment so yes at low 820 00:38:17,620 --> 00:38:15,630 nitrogen particularly offshore one might 821 00:38:19,730 --> 00:38:17,630 favor cyanobacteria 822 00:38:22,820 --> 00:38:19,740 one of the things that I think will 823 00:38:25,520 --> 00:38:22,830 build up nitrate availability in the 824 00:38:28,850 --> 00:38:25,530 oceans is simply as you create a more 825 00:38:31,370 --> 00:38:28,860 oxic redox profile and that I think is 826 00:38:32,810 --> 00:38:31,380 ultimately driven by phosphorus so yes 827 00:38:35,180 --> 00:38:32,820 it's important but yes it's not 828 00:38:42,510 --> 00:38:35,190 independent of what's going on with 829 00:38:48,160 --> 00:38:45,730 do you see any changes in the physiology 830 00:38:52,360 --> 00:38:48,170 or the shapes of eukaryotic like its 831 00:38:55,300 --> 00:38:52,370 protists at the Joey well we don't have 832 00:38:59,830 --> 00:38:55,310 any the oldest fossil evidence that we 833 00:39:01,480 --> 00:38:59,840 have for eukaryotes is about between 834 00:39:04,480 --> 00:39:01,490 sixteen hundred and sixteen hundred and 835 00:39:06,190 --> 00:39:04,490 fifty million million years ago now 836 00:39:08,500 --> 00:39:06,200 having said that one has to be honest 837 00:39:10,210 --> 00:39:08,510 and say that the the quality of the 838 00:39:13,120 --> 00:39:10,220 record per se just gets worse and worse 839 00:39:15,940 --> 00:39:13,130 as you go go backward through time but 840 00:39:18,310 --> 00:39:15,950 no we have there prokaryotes and well 841 00:39:21,510 --> 00:39:18,320 firfer prokaryotes well I think what 842 00:39:24,280 --> 00:39:21,520 happens that is very different is that 843 00:39:27,700 --> 00:39:24,290 to the extent that sign of bacteria 844 00:39:30,610 --> 00:39:27,710 existed in the Archaean earth their 845 00:39:33,160 --> 00:39:30,620 population sizes and oxygen fluxes 846 00:39:35,950 --> 00:39:33,170 associated with those were insufficient 847 00:39:40,870 --> 00:39:35,960 to essentially titrate out all the sinks 848 00:39:43,990 --> 00:39:40,880 for oxygen what happens at the goe is 849 00:39:47,290 --> 00:39:44,000 that again because of oxygen produced by 850 00:39:49,990 --> 00:39:47,300 sign of bacteria you end up oxygenating 851 00:39:51,910 --> 00:39:50,000 the surface ocean and atmosphere and 852 00:39:53,500 --> 00:39:51,920 that that shows I think an important 853 00:39:57,600 --> 00:39:53,510 thing that saina bacteria end up being 854 00:40:01,300 --> 00:39:57,610 ecosystem engineers in that through that 855 00:40:04,420 --> 00:40:01,310 process associated with the oxygen they 856 00:40:08,560 --> 00:40:04,430 produce you basically produce photic 857 00:40:10,990 --> 00:40:08,570 zones in which the alternative electron 858 00:40:14,050 --> 00:40:11,000 donors things like sulphide and ferrous 859 00:40:16,420 --> 00:40:14,060 iron are simply no longer there so I 860 00:40:19,890 --> 00:40:16,430 think that's the big difference then is 861 00:40:23,710 --> 00:40:19,900 sign of bacteria either go from being 862 00:40:26,560 --> 00:40:23,720 absent or a smaller part of ecosystems 863 00:40:28,210 --> 00:40:26,570 to being dominant primary producers and 864 00:40:31,260 --> 00:40:28,220 of course we don't see this in the 865 00:40:33,340 --> 00:40:31,270 fossil record but as once you get 866 00:40:36,810 --> 00:40:33,350 metabolically significant amounts of 867 00:40:40,390 --> 00:40:36,820 oxygen and in the atmosphere then you 868 00:40:43,480 --> 00:40:40,400 dramatically expand respiratory 869 00:40:45,700 --> 00:40:43,490 capabilities chemoautotrophs abilities 870 00:40:49,320 --> 00:40:45,710 biosynthetic capabilities and I think 871 00:40:51,610 --> 00:40:49,330 you see you see some evidence of that in 872 00:40:53,260 --> 00:40:51,620 phylogeny but not directly 873 00:40:55,030 --> 00:40:53,270 in the fossil record but as an 874 00:40:56,560 --> 00:40:55,040 extinction event do you think it Trump's 875 00:40:58,750 --> 00:40:56,570 the one that you just described you know 876 00:41:01,720 --> 00:40:58,760 lynn margulis bless her soul always used 877 00:41:04,870 --> 00:41:01,730 to talk I think unfortunately about the 878 00:41:07,630 --> 00:41:04,880 the oxygen Holocaust and she had this 879 00:41:09,880 --> 00:41:07,640 sense that basically the world was full 880 00:41:12,820 --> 00:41:09,890 of anaerobes and as oxygen comes up they 881 00:41:15,270 --> 00:41:12,830 all die actually what they all did was 882 00:41:17,170 --> 00:41:15,280 went a millimeter beneath the surface 883 00:41:20,230 --> 00:41:17,180 where there's still an toxic 884 00:41:22,840 --> 00:41:20,240 environments so III tend to think of the 885 00:41:25,330 --> 00:41:22,850 goe as expanding the ecological 886 00:41:27,400 --> 00:41:25,340 amplitude not simply changing it in a 887 00:41:37,590 --> 00:41:27,410 way that fundamentally drives most 888 00:41:40,480 --> 00:41:37,600 earlier life out of existence is 889 00:41:43,240 --> 00:41:40,490 basically to our scenario and you have 890 00:41:45,940 --> 00:41:43,250 continually than the kind of work and I 891 00:41:49,840 --> 00:41:45,950 have let your papers from your vantage 892 00:41:51,940 --> 00:41:49,850 and my question as a I'm geologist and 893 00:41:54,520 --> 00:41:51,950 we have worked over the world it's more 894 00:41:57,970 --> 00:41:54,530 than 100 localities over 30 years and 895 00:42:01,360 --> 00:41:57,980 then the Archaean is a kind of know 896 00:42:03,910 --> 00:42:01,370 segment dialogues in the area so that 897 00:42:07,750 --> 00:42:03,920 therefore in your opinion ok quite a few 898 00:42:09,580 --> 00:42:07,760 amounts of nutrients provided and the 899 00:42:14,050 --> 00:42:09,590 fire's work with emergence of huge 900 00:42:14,530 --> 00:42:14,060 animals because large amounts of cement 901 00:42:18,040 --> 00:42:14,540 airlocks 902 00:42:21,130 --> 00:42:18,050 appeared that's fine and then probably 903 00:42:24,400 --> 00:42:21,140 the assail bacteria produce oxygen and 904 00:42:27,820 --> 00:42:24,410 oxygen pumped have been very productive 905 00:42:31,390 --> 00:42:27,830 so the used mentioned okay itself as 906 00:42:36,930 --> 00:42:31,400 high as long low oxygen intermediate and 907 00:42:43,180 --> 00:42:36,940 high oxygen so there is the okay then 908 00:42:48,340 --> 00:42:43,190 life change very simple one progeria 909 00:42:54,340 --> 00:42:48,350 right and then endosymbiont and then we 910 00:42:58,150 --> 00:42:54,350 are multiple architecture including 911 00:43:02,050 --> 00:42:58,160 everything right so that okay i my 912 00:43:05,320 --> 00:43:02,060 question is what is the most important 913 00:43:08,320 --> 00:43:05,330 environmental pressure to change 914 00:43:13,420 --> 00:43:08,330 the system of life okay that's a very 915 00:43:15,580 --> 00:43:13,430 good question and I I think I moved over 916 00:43:18,130 --> 00:43:15,590 a slide bite from a review of Tim 917 00:43:20,170 --> 00:43:18,140 Lyons's papers quickly but other people 918 00:43:22,420 --> 00:43:20,180 have shown similar things that I think 919 00:43:26,650 --> 00:43:22,430 that most of us would agree that before 920 00:43:29,110 --> 00:43:26,660 the goe o - tensions were very very low 921 00:43:31,390 --> 00:43:29,120 ten to the minus five PA L or something 922 00:43:34,530 --> 00:43:31,400 like that that you permanently have a 923 00:43:36,700 --> 00:43:34,540 transition to a world that at least has 924 00:43:40,960 --> 00:43:36,710 something like a few percent of today's 925 00:43:43,630 --> 00:43:40,970 oxygen levels in the Proterozoic and 926 00:43:45,310 --> 00:43:43,640 that persists it's usually shown as a 927 00:43:47,110 --> 00:43:45,320 straight line but that's a line of 928 00:43:49,090 --> 00:43:47,120 ignorance it could go up and down we 929 00:43:53,560 --> 00:43:49,100 don't don't really know what's going on 930 00:43:56,440 --> 00:43:53,570 but all the sedimentary geochemical 931 00:44:01,240 --> 00:43:56,450 indicators tell us that we are moving to 932 00:44:04,450 --> 00:44:01,250 a world with more completely oxic radix 933 00:44:07,030 --> 00:44:04,460 profiles about the time that animals 934 00:44:09,550 --> 00:44:07,040 come in so yes I think there is a 935 00:44:12,430 --> 00:44:09,560 history of increasing oxygen there's a 936 00:44:16,750 --> 00:44:12,440 paper just came out by two geologists in 937 00:44:21,760 --> 00:44:16,760 the United States John Husson and I'm 938 00:44:25,120 --> 00:44:21,770 just blanking on Ola shut Shannon Peters 939 00:44:26,800 --> 00:44:25,130 in which they actually argue what may be 940 00:44:29,740 --> 00:44:26,810 similar to what your thinking is that 941 00:44:32,140 --> 00:44:29,750 you simply have more erosion and more 942 00:44:34,660 --> 00:44:32,150 sediments in the phanerozoic than you 943 00:44:37,660 --> 00:44:34,670 did earlier and that's what drives this 944 00:44:40,180 --> 00:44:37,670 oxygen change I think the problem is we 945 00:44:43,600 --> 00:44:40,190 know that there is a decay curve that 946 00:44:46,300 --> 00:44:43,610 the older the sedimentary unit the more 947 00:44:49,360 --> 00:44:46,310 likely it has been eroded so I think 948 00:44:52,080 --> 00:44:49,370 that it I would agree with previous 949 00:44:55,180 --> 00:44:52,090 speakers that you probably have less 950 00:44:57,220 --> 00:44:55,190 exposed landmass and at least much of of 951 00:44:59,950 --> 00:44:57,230 the Archaean and that may change 952 00:45:02,710 --> 00:44:59,960 nutrient levels I think the difference 953 00:45:06,280 --> 00:45:02,720 in preserved sediments between the 954 00:45:10,960 --> 00:45:06,290 Proterozoic and phanerozoic may well be 955 00:45:13,200 --> 00:45:10,970 a question of preservation so to get at 956 00:45:16,450 --> 00:45:13,210 your question then the what people have 957 00:45:18,190 --> 00:45:16,460 stopped doing is saying why was there 1 958 00:45:21,190 --> 00:45:18,200 percent of today's levels 959 00:45:24,870 --> 00:45:21,200 in the Proterozoic or I say stop saying 960 00:45:26,920 --> 00:45:24,880 why did oxygen change at these two 961 00:45:29,319 --> 00:45:26,930 junctures at the beginning end of the 962 00:45:31,300 --> 00:45:29,329 Proterozoic but rather say what 963 00:45:34,300 --> 00:45:31,310 conditions would actually maintain a 964 00:45:36,700 --> 00:45:34,310 long-term steady state of these three 965 00:45:39,579 --> 00:45:36,710 different types and again that that 966 00:45:42,089 --> 00:45:39,589 appears to go perhaps more than anything 967 00:45:45,880 --> 00:45:42,099 else it's a nutrient availability 968 00:45:47,470 --> 00:45:45,890 especially phosphorus and the important 969 00:45:51,099 --> 00:45:47,480 thing that's becoming clearer and 970 00:45:53,859 --> 00:45:51,109 clearer is that in a world where anoxic 971 00:45:57,520 --> 00:45:53,869 water masses are rich in ferrous iron 972 00:46:00,730 --> 00:45:57,530 there are important sinks for phosphate 973 00:46:04,000 --> 00:46:00,740 that marine geochemists haven't thought 974 00:46:06,520 --> 00:46:04,010 about until recently soil chemists knew 975 00:46:08,050 --> 00:46:06,530 about these thirty years ago but marine 976 00:46:11,230 --> 00:46:08,060 chemists are just starting 977 00:46:14,220 --> 00:46:11,240 sorry to interrupt but sorry my final 978 00:46:18,670 --> 00:46:14,230 important question is the why life 979 00:46:23,020 --> 00:46:18,680 selected okay at the side for example 1 980 00:46:26,770 --> 00:46:23,030 million bigger for pre-k Eukarya and 981 00:46:30,010 --> 00:46:26,780 another 1 million and two bigger that is 982 00:46:33,849 --> 00:46:30,020 us but multiple assemblage of many 983 00:46:36,400 --> 00:46:33,859 different ok organisms I understand the 984 00:46:39,579 --> 00:46:36,410 question that I I driving horse yeah I I 985 00:46:43,599 --> 00:46:39,589 think there are example is there there 986 00:46:45,880 --> 00:46:43,609 are diffusion plays a very important 987 00:46:48,250 --> 00:46:45,890 role on amending the size of organisms 988 00:46:50,589 --> 00:46:48,260 and I think bacteria are largely small 989 00:46:52,690 --> 00:46:50,599 because of diffusion and the nature 990 00:46:55,240 --> 00:46:52,700 there's their cytosol 991 00:46:57,040 --> 00:46:55,250 eukaryotes which have a different 992 00:46:59,470 --> 00:46:57,050 internal architecture can be somewhat 993 00:47:01,980 --> 00:46:59,480 larger but are still diffusion limited 994 00:47:04,960 --> 00:47:01,990 the nice thing about animals at least 995 00:47:06,849 --> 00:47:04,970 once you start climbing the animal tree 996 00:47:11,559 --> 00:47:06,859 is that they have to have structures 997 00:47:13,660 --> 00:47:11,569 that essentially get around the limits 998 00:47:17,079 --> 00:47:13,670 of diffusion ever you I'm usually the 999 00:47:19,589 --> 00:47:17,089 most oxidized oh I think in some ways 1000 00:47:24,640 --> 00:47:19,599 it's it's then the relationship between 1001 00:47:27,960 --> 00:47:24,650 the physiological capabilities of an 1002 00:47:30,360 --> 00:47:27,970 organism they're related to size and 1003 00:47:33,840 --> 00:47:30,370 essentially the amount of 1004 00:47:36,150 --> 00:47:33,850 oxygen which in turn actually does go 1005 00:47:39,300 --> 00:47:36,160 back to things like phosphorus 1006 00:47:40,680 --> 00:47:39,310 availability so it's it's it's not us at 1007 00:47:42,710 --> 00:47:40,690 least I don't think there's a simple 1008 00:47:46,650 --> 00:47:42,720 magic wand but I think it's this 1009 00:47:59,090 --> 00:47:46,660 interconnectedness that goes from really 1010 00:48:02,060 --> 00:47:59,100 physiology to tectonics thank you okay 1011 00:48:05,730 --> 00:48:02,070 it's a related question to the 1012 00:48:07,400 --> 00:48:05,740 phosphorus story you just suggested so 1013 00:48:09,360 --> 00:48:07,410 one implication of that is that 1014 00:48:12,570 --> 00:48:09,370 continental weathering rates may have 1015 00:48:14,310 --> 00:48:12,580 been constant for a million years which 1016 00:48:17,580 --> 00:48:14,320 is interesting to think about yeah it 1017 00:48:19,110 --> 00:48:17,590 really is and again when you look at the 1018 00:48:20,820 --> 00:48:19,120 Tim Lyons curve and you showed something 1019 00:48:25,170 --> 00:48:20,830 like it 1020 00:48:26,730 --> 00:48:25,180 it shows the atmosphere being you know 1021 00:48:27,570 --> 00:48:26,740 having a constant composition for a 1022 00:48:30,000 --> 00:48:27,580 billion years 1023 00:48:34,140 --> 00:48:30,010 we don't know that that's true all we 1024 00:48:37,890 --> 00:48:34,150 know is that it never dipped below back 1025 00:48:40,620 --> 00:48:37,900 into a atmospheric anoxia and it never 1026 00:48:44,820 --> 00:48:40,630 reached a state where you essentially 1027 00:48:47,400 --> 00:48:44,830 eliminated all of the subsurface an 1028 00:48:50,400 --> 00:48:47,410 toxic water masses but that means it 1029 00:48:52,770 --> 00:48:50,410 probably varies within a certain level 1030 00:48:56,790 --> 00:48:52,780 so yeah it could be what I don't 1031 00:48:59,000 --> 00:48:56,800 understand just that the the pro the 1032 00:49:03,270 --> 00:48:59,010 middle of the part of the Proterozoic 1033 00:49:07,020 --> 00:49:03,280 where the carbon isotopic curve is is 1034 00:49:08,670 --> 00:49:07,030 flat which is odd where you have and you 1035 00:49:12,360 --> 00:49:08,680 know more about this and I do an toxic 1036 00:49:17,070 --> 00:49:12,370 and orogenic Granite's odd structures 1037 00:49:20,340 --> 00:49:17,080 and petrology sometimes called the 1038 00:49:22,620 --> 00:49:20,350 boring billion you know what's really 1039 00:49:26,370 --> 00:49:22,630 going what fundamentally I don't think I 1040 00:49:28,380 --> 00:49:26,380 understand the tectonics of that portion 1041 00:49:31,140 --> 00:49:28,390 of Earth history but it does seem to be 1042 00:49:33,780 --> 00:49:31,150 at least qualitatively somewhat distinct 1043 00:49:37,320 --> 00:49:33,790 from the phanerozoic tectonics that we 1044 00:49:41,110 --> 00:49:37,330 understand and earlier stuff that's the 1045 00:49:44,590 --> 00:49:43,460 so let's thank the speaker again thank 1046 00:49:47,240 --> 00:49:44,600 you much 1047 00:49:49,850 --> 00:49:47,250 [Applause] 1048 00:49:51,950 --> 00:49:49,860 before closing decision we'll make an 1049 00:49:55,550 --> 00:49:51,960 announcement for the poster presenters 1050 00:49:58,100 --> 00:49:55,560 please remove your posters during this 1051 00:50:01,520 --> 00:49:58,110 next coffee break because so that we can 1052 00:50:02,960 --> 00:50:01,530 clean that room so let's thank the 1053 00:50:06,770 --> 00:50:02,970 speaker again and thank you very much