1
00:00:00,260 --> 00:00:11,740
[Music]

2
00:00:15,250 --> 00:00:14,060
all right well thank you everyone for

3
00:00:17,300 --> 00:00:15,260
having me

4
00:00:19,820 --> 00:00:17,310
before I begin I just want to very

5
00:00:22,820 --> 00:00:19,830
briefly acknowledge my co-authors so the

6
00:00:24,170 --> 00:00:22,830
first is my PhD advisor Phil shop as

7
00:00:26,390 --> 00:00:24,180
well as our lab member and research

8
00:00:29,050 --> 00:00:26,400
scientist Anatoly could you add Saif who

9
00:00:31,520 --> 00:00:29,060
contributed a great deal to this work

10
00:00:34,010 --> 00:00:31,530
okay so really one of the most

11
00:00:35,959 --> 00:00:34,020
fundamental aspects of our planets

12
00:00:38,300 --> 00:00:35,969
evolution has been the history of

13
00:00:40,040 --> 00:00:38,310
oxygenation of our oceans and

14
00:00:41,900 --> 00:00:40,050
atmospheres and so this is from the

15
00:00:44,180 --> 00:00:41,910
Hadean and our kin which essentially had

16
00:00:45,620 --> 00:00:44,190
no free oxygen available all the way

17
00:00:47,270 --> 00:00:45,630
through our current atmospheric

18
00:00:49,340 --> 00:00:47,280
composition of about 20%

19
00:00:50,780 --> 00:00:49,350
I want to thank Becky this morning for

20
00:00:52,460 --> 00:00:50,790
giving a really nice overview of a

21
00:00:55,460 --> 00:00:52,470
geologic time scale so I don't have to

22
00:00:58,130 --> 00:00:55,470
go into all those details so pictured

23
00:01:01,340 --> 00:00:58,140
here is our general currently understood

24
00:01:03,160 --> 00:01:01,350
model of earth oxygenation and so what

25
00:01:05,719 --> 00:01:03,170
we see is that really the first

26
00:01:07,459 --> 00:01:05,729
accumulation of oxygen in the atmosphere

27
00:01:08,870 --> 00:01:07,469
occurred at about two and a half billion

28
00:01:11,719 --> 00:01:08,880
years ago this is the great oxidation

29
00:01:13,160 --> 00:01:11,729
event that's very well known but today

30
00:01:14,990 --> 00:01:13,170
I'm going to be focusing on this more

31
00:01:17,810 --> 00:01:15,000
recent time here this is two billion

32
00:01:20,750 --> 00:01:17,820
years later so this isn't a time period

33
00:01:23,270 --> 00:01:20,760
between the neoproterozoic and Cambrian

34
00:01:24,770 --> 00:01:23,280
transition and understanding the history

35
00:01:27,140 --> 00:01:24,780
of oxygenation during this time is

36
00:01:28,910 --> 00:01:27,150
particularly important because it's also

37
00:01:31,250 --> 00:01:28,920
at this time that we see in the fossil

38
00:01:33,170 --> 00:01:31,260
record the earliest evidence of a rapid

39
00:01:35,000 --> 00:01:33,180
diversification of oxygen breathing

40
00:01:38,719 --> 00:01:35,010
animals so this is otherwise known as

41
00:01:40,880 --> 00:01:38,729
the Cambrian explosion and so because of

42
00:01:43,219 --> 00:01:40,890
this this this general increase in

43
00:01:45,380 --> 00:01:43,229
oxygen during this time has been invoked

44
00:01:48,230 --> 00:01:45,390
as being potentially an environmental

45
00:01:50,060 --> 00:01:48,240
trigger of this evolution of increasing

46
00:01:51,130 --> 00:01:50,070
biological complexity this may or may

47
00:01:54,140 --> 00:01:51,140
not actually have been the case

48
00:01:56,270 --> 00:01:54,150
nevertheless in order to further explore

49
00:01:58,580 --> 00:01:56,280
the coevolution of life in the physical

50
00:02:00,620 --> 00:01:58,590
environment during this time as well as

51
00:02:02,420 --> 00:02:00,630
to understand the controlling factors of

52
00:02:04,429 --> 00:02:02,430
how we get the development and

53
00:02:06,859 --> 00:02:04,439
distribution of complex life both on our

54
00:02:08,869 --> 00:02:06,869
world and on other world it's necessary

55
00:02:10,520 --> 00:02:08,879
to better constrain both the magnitude

56
00:02:13,850 --> 00:02:10,530
and timing this history of oxygenation

57
00:02:16,010 --> 00:02:13,860
here so I will mention that this is a

58
00:02:16,970 --> 00:02:16,020
far from understudied area there are

59
00:02:18,710 --> 00:02:16,980
currently

60
00:02:20,479 --> 00:02:18,720
variety of both biological and

61
00:02:21,699 --> 00:02:20,489
geological proxies for understanding

62
00:02:24,649 --> 00:02:21,709
oxygenation during this time

63
00:02:27,589 --> 00:02:24,659
nevertheless though these various

64
00:02:29,300 --> 00:02:27,599
proxies do come with their associated

65
00:02:31,190 --> 00:02:29,310
strengths and uncertainties we're still

66
00:02:33,740 --> 00:02:31,200
left with a relatively qualitative view

67
00:02:35,720 --> 00:02:33,750
of oxygenation during this time and so

68
00:02:36,860 --> 00:02:35,730
it's our focus here to improve

69
00:02:39,199 --> 00:02:36,870
especially the quantitative

70
00:02:41,690 --> 00:02:39,209
understanding of particularly marine

71
00:02:43,400 --> 00:02:41,700
neoproterozoic and Cambrian oxygenation

72
00:02:45,530 --> 00:02:43,410
through the development of a more

73
00:02:48,949 --> 00:02:45,540
quantitative oxygen proxy or what we're

74
00:02:50,839 --> 00:02:48,959
calling an oxygen pareo barometer so

75
00:02:52,910 --> 00:02:50,849
what we've been looking at at the same

76
00:02:54,319 --> 00:02:52,920
time during this this increase in

77
00:02:56,360 --> 00:02:54,329
oxygenation we also see something

78
00:02:58,699 --> 00:02:56,370
special which is a neoproterozoic

79
00:03:00,949 --> 00:02:58,709
Cambrian phosphate Jenica vent and this

80
00:03:02,809 --> 00:03:00,959
is perhaps the largest and most globally

81
00:03:05,690 --> 00:03:02,819
extensive fossil genic event in Earth's

82
00:03:09,490 --> 00:03:05,700
history so what we see during phospho

83
00:03:11,960 --> 00:03:09,500
Genesis is the extensive global

84
00:03:14,030 --> 00:03:11,970
deposition of what are called phosphates

85
00:03:17,869 --> 00:03:14,040
so these are sediments for a phosphate

86
00:03:19,520 --> 00:03:17,879
rich geologic deposits for this time for

87
00:03:21,170 --> 00:03:19,530
the phosphates of these ages these are

88
00:03:23,240 --> 00:03:21,180
currently known from essentially every

89
00:03:24,379 --> 00:03:23,250
continent except Antarctica whether or

90
00:03:26,690 --> 00:03:24,389
not they're actually there and we just

91
00:03:27,860 --> 00:03:26,700
haven't found them we don't know so here

92
00:03:30,110 --> 00:03:27,870
you can see the geographic distribution

93
00:03:31,580 --> 00:03:30,120
as well as the age distribution down

94
00:03:33,229 --> 00:03:31,590
here on the bottom you can see that they

95
00:03:35,059 --> 00:03:33,239
cluster more or less within about 100

96
00:03:37,190 --> 00:03:35,069
million years of the neoproterozoic

97
00:03:38,780 --> 00:03:37,200
Cambrian boundary here and it's also

98
00:03:40,370 --> 00:03:38,790
important to note that for the most part

99
00:03:42,949 --> 00:03:40,380
these are shallow marine deposits and

100
00:03:46,159 --> 00:03:42,959
they contain abundant amounts of micro

101
00:03:47,780 --> 00:03:46,169
fossils ok so another reason why

102
00:03:49,430 --> 00:03:47,790
phosphates are important to study is

103
00:03:51,349 --> 00:03:49,440
that they concentrate phosphate in the

104
00:03:52,940 --> 00:03:51,359
mineral called apatite apatite is the

105
00:03:54,920 --> 00:03:52,950
same mineral that makes up our bones in

106
00:03:57,409 --> 00:03:54,930
our teeth if the calcium phosphate

107
00:03:59,930 --> 00:03:57,419
mineral and it's particularly well known

108
00:04:01,849 --> 00:03:59,940
in geology and that it incorporates a

109
00:04:04,339 --> 00:04:01,859
relatively high abundance of rare earth

110
00:04:05,960 --> 00:04:04,349
elements these are important typically

111
00:04:07,610 --> 00:04:05,970
in geologic applications because they

112
00:04:09,349 --> 00:04:07,620
usually carry with them some amount of

113
00:04:11,659 --> 00:04:09,359
petrographic and environmental

114
00:04:14,420 --> 00:04:11,669
information rare earth elements can

115
00:04:16,789 --> 00:04:14,430
substitute at two different calcium

116
00:04:18,140 --> 00:04:16,799
sites in the apatite structure two

117
00:04:20,060 --> 00:04:18,150
different sites very simply named the

118
00:04:21,860 --> 00:04:20,070
calcium one site and the calcium 2 site

119
00:04:24,860 --> 00:04:21,870
you can see from this figure that these

120
00:04:27,200 --> 00:04:24,870
- yeah very simple these two sites are

121
00:04:28,000 --> 00:04:27,210
different both in their local structural

122
00:04:30,940 --> 00:04:28,010
geometry

123
00:04:32,290 --> 00:04:30,950
symmetry but the problem occurs that

124
00:04:34,330 --> 00:04:32,300
rare earth elements are typically

125
00:04:36,670 --> 00:04:34,340
existing in the trivalent state and so

126
00:04:40,180 --> 00:04:36,680
in order to substitute a trivalent rare

127
00:04:42,100 --> 00:04:40,190
earth element in for a divalent calcium

128
00:04:44,800 --> 00:04:42,110
ion you have to go through a very

129
00:04:47,200 --> 00:04:44,810
particular substitution mechanism and so

130
00:04:49,390 --> 00:04:47,210
both observational and experimental

131
00:04:51,130 --> 00:04:49,400
evidence that suggested that at the

132
00:04:52,960 --> 00:04:51,140
calcium one site you get the

133
00:04:54,730 --> 00:04:52,970
substitution of a trivalent rare earth

134
00:04:56,740 --> 00:04:54,740
element for calcium through the

135
00:04:58,960 --> 00:04:56,750
incorporation of an additional vacancy

136
00:05:00,910 --> 00:04:58,970
so and in that sense you're essentially

137
00:05:03,520 --> 00:05:00,920
substituting two rare earth elements for

138
00:05:05,350 --> 00:05:03,530
three calcium ions but for the calcium

139
00:05:07,780 --> 00:05:05,360
to site this is where it becomes special

140
00:05:09,250 --> 00:05:07,790
for for our purposes is you get this

141
00:05:12,640 --> 00:05:09,260
double substitution of a rare earth

142
00:05:15,100 --> 00:05:12,650
element for calcium ion accompanying a

143
00:05:17,770 --> 00:05:15,110
substitution of an oxygen ion for a

144
00:05:19,210 --> 00:05:17,780
native anion usually with the case of

145
00:05:21,730 --> 00:05:19,220
apatite it's typically fluoride

146
00:05:23,680 --> 00:05:21,740
hydroxide or chloride and so it's here

147
00:05:25,810 --> 00:05:23,690
that we see in oxygen dependent

148
00:05:28,930 --> 00:05:25,820
mechanism pretty incorporation of rare

149
00:05:30,250 --> 00:05:28,940
earth elements and apatite so another

150
00:05:32,080 --> 00:05:30,260
thing that happens when you get birth

151
00:05:34,930 --> 00:05:32,090
elements into apatite is you make that

152
00:05:36,970 --> 00:05:34,940
apatite fluorescent so pictured here are

153
00:05:39,360 --> 00:05:36,980
two different fluorescence spectra this

154
00:05:42,730 --> 00:05:39,370
is a oops sorry this is a figure from

155
00:05:45,310 --> 00:05:42,740
gas pedal and so what they did was they

156
00:05:47,080 --> 00:05:45,320
artificially substituted samarium in

157
00:05:49,780 --> 00:05:47,090
apatite mineral and so the way you

158
00:05:51,040 --> 00:05:49,790
accomplish this is you take apatite and

159
00:05:52,660 --> 00:05:51,050
you take a source of Sumeria and you

160
00:05:55,780 --> 00:05:52,670
heat them to a high temperature in close

161
00:05:57,400 --> 00:05:55,790
proximity and that therefore facilitates

162
00:06:00,070 --> 00:05:57,410
the diffusion of samarium into the

163
00:06:02,050 --> 00:06:00,080
apatite crystal structure it measured

164
00:06:04,000 --> 00:06:02,060
them using fluorescence spectroscopy and

165
00:06:05,680 --> 00:06:04,010
they they did this heating experiment

166
00:06:07,120 --> 00:06:05,690
under two different conditions and so

167
00:06:08,740 --> 00:06:07,130
these two fluorescence spectra are

168
00:06:12,100 --> 00:06:08,750
representative of those two conditions

169
00:06:15,040 --> 00:06:12,110
in the red they did this heating process

170
00:06:16,570 --> 00:06:15,050
in a vacuum therefore resulting in the

171
00:06:19,420 --> 00:06:16,580
substitution of samarium in the calcium

172
00:06:22,210 --> 00:06:19,430
one site and they also did this with the

173
00:06:23,620 --> 00:06:22,220
green spectrum in air and so with this

174
00:06:26,080 --> 00:06:23,630
case you get the substitution of

175
00:06:29,140 --> 00:06:26,090
samarium the calcium to site in an

176
00:06:30,700 --> 00:06:29,150
oxygen dependent manner and so for these

177
00:06:33,370 --> 00:06:30,710
fluorescence spectra the spectral

178
00:06:35,440 --> 00:06:33,380
variability which is inherent to the the

179
00:06:37,390 --> 00:06:35,450
local structural effects of the calcium

180
00:06:39,790 --> 00:06:37,400
sites where samarium is substituting

181
00:06:41,980 --> 00:06:39,800
this really depends the variability

182
00:06:45,460 --> 00:06:41,990
depends on the presence of oxygen there

183
00:06:47,560 --> 00:06:45,470
samarium substitution okay so for the

184
00:06:49,150 --> 00:06:47,570
development of an appetite auction paleo

185
00:06:50,530 --> 00:06:49,160
barometer that takes advantage of this

186
00:06:52,930 --> 00:06:50,540
process we followed the following

187
00:06:54,880 --> 00:06:52,940
strategy the first is an experimental

188
00:06:56,890 --> 00:06:54,890
calibration of this fluorescence

189
00:06:58,480 --> 00:06:56,900
variability and so we've followed the

190
00:07:01,150 --> 00:06:58,490
same process of artificially

191
00:07:03,340 --> 00:07:01,160
substituting samarium and apatite under

192
00:07:05,650 --> 00:07:03,350
varying oxygen concentrations and then

193
00:07:08,560 --> 00:07:05,660
we follow that with the development of a

194
00:07:11,140 --> 00:07:08,570
quantifiable metric for assessing that

195
00:07:13,510 --> 00:07:11,150
spectral variability and then we took

196
00:07:16,150 --> 00:07:13,520
that metric and applied them to natural

197
00:07:17,650 --> 00:07:16,160
neoproterozoic and Cambrian age appetite

198
00:07:19,900 --> 00:07:17,660
specimens in order to then back

199
00:07:23,050 --> 00:07:19,910
calculate an estimate past local oxygen

200
00:07:24,790 --> 00:07:23,060
and so all of this with the general goal

201
00:07:28,240 --> 00:07:24,800
of really quantifying shallow marine

202
00:07:29,980 --> 00:07:28,250
oxygenation during this event okay so

203
00:07:32,440 --> 00:07:29,990
for the experimental calibration into

204
00:07:35,530 --> 00:07:32,450
the following so we we took these

205
00:07:37,870 --> 00:07:35,540
apatite powder and samarium pellets and

206
00:07:39,970 --> 00:07:37,880
compressed them heated them in a furnace

207
00:07:42,130 --> 00:07:39,980
in 900 degrees Celsius under varying

208
00:07:44,050 --> 00:07:42,140
levels of oxygen and then measured them

209
00:07:46,900 --> 00:07:44,060
using fluorescence spectroscopy and so

210
00:07:48,940 --> 00:07:46,910
what we see is this spectral variability

211
00:07:50,650 --> 00:07:48,950
that's transition from zero percent

212
00:07:52,900 --> 00:07:50,660
oxygen available to twenty percent

213
00:07:55,210 --> 00:07:52,910
oxygen this is just our current air

214
00:07:56,890 --> 00:07:55,220
composition and so we see is this

215
00:07:59,110 --> 00:07:56,900
transition and spectral character

216
00:08:00,430 --> 00:07:59,120
particularly in these two spectral

217
00:08:03,160 --> 00:08:00,440
ranges that are highlighted in these

218
00:08:05,470 --> 00:08:03,170
colored bars more specifically what we

219
00:08:07,450 --> 00:08:05,480
see is that as you go towards more

220
00:08:10,420 --> 00:08:07,460
anoxic experimental conditions you see

221
00:08:13,990 --> 00:08:10,430
the the increased intensity of

222
00:08:16,660 --> 00:08:14,000
fluorescence Peaks at the 607 and 654

223
00:08:18,220 --> 00:08:16,670
nanometer wavelength positions indicated

224
00:08:21,220 --> 00:08:18,230
by these red bars hope you can see them

225
00:08:23,380 --> 00:08:21,230
and as you go towards more toxic

226
00:08:25,300 --> 00:08:23,390
experimental conditions you instead see

227
00:08:28,720 --> 00:08:25,310
the increasing intensity of bands at the

228
00:08:30,880 --> 00:08:28,730
605 and 650 tune animated regions and so

229
00:08:33,130 --> 00:08:30,890
here you get samarium substitution the

230
00:08:34,540 --> 00:08:33,140
calcium one site and for the oxy case

231
00:08:37,390 --> 00:08:34,550
you get Sumerian substitution or the

232
00:08:38,650 --> 00:08:37,400
calcium 2 site and so for the for the

233
00:08:41,140 --> 00:08:38,660
rest of the talk will be kind of talking

234
00:08:42,970 --> 00:08:41,150
about these bands as oxic associated

235
00:08:44,620 --> 00:08:42,980
fluorescence signatures and these are

236
00:08:47,860 --> 00:08:44,630
anoxic associated fluorescence

237
00:08:50,140 --> 00:08:47,870
signatures ok so in order to quantify

238
00:08:51,760 --> 00:08:50,150
the spectral variability we followed a

239
00:08:54,700 --> 00:08:51,770
relatively standard peak fitting

240
00:08:55,390 --> 00:08:54,710
procedure where we are interested in in

241
00:08:57,760 --> 00:08:55,400
a sense ray

242
00:09:00,360 --> 00:08:57,770
showing the relative intensities of

243
00:09:03,280 --> 00:09:00,370
these oxic and anoxic associative Peaks

244
00:09:04,810 --> 00:09:03,290
so did this really simple calculation

245
00:09:07,210 --> 00:09:04,820
it's just the area of an ox ik

246
00:09:09,880 --> 00:09:07,220
associated peak divided by the sum

247
00:09:12,370 --> 00:09:09,890
Daria's of a neighboring anoxic

248
00:09:14,230 --> 00:09:12,380
associate began the oxy peak and so what

249
00:09:16,600 --> 00:09:14,240
you get what we're calling is an

250
00:09:18,370 --> 00:09:16,610
appetite auction paleo barometer at AOP

251
00:09:20,410 --> 00:09:18,380
value somewhere between zero and one

252
00:09:22,510 --> 00:09:20,420
where a value of zero would indicate

253
00:09:25,750 --> 00:09:22,520
only the presence of these anoxic

254
00:09:28,060 --> 00:09:25,760
associated Peaks a value of sorry value

255
00:09:29,950 --> 00:09:28,070
of zero yes and the value of one would

256
00:09:32,560 --> 00:09:29,960
indicate the presence of only the oxic

257
00:09:36,310 --> 00:09:32,570
associated piece if you then plot these

258
00:09:38,200 --> 00:09:36,320
AOP values against the percentage oxygen

259
00:09:40,810 --> 00:09:38,210
that we used in the experiments we see a

260
00:09:43,180 --> 00:09:40,820
good agreement between these two these Q

261
00:09:44,890 --> 00:09:43,190
values and we also see this kind of

262
00:09:49,030 --> 00:09:44,900
characteristic curve here where we see a

263
00:09:51,160 --> 00:09:49,040
very steep slope between aoki values and

264
00:09:54,030 --> 00:09:51,170
oxygen the very low oxygen levels and

265
00:09:56,980 --> 00:09:54,040
then it sort of tapers off in plateaus

266
00:09:58,510 --> 00:09:56,990
okay so that that curve is essentially

267
00:10:00,220 --> 00:09:58,520
the calibration curve that we're using

268
00:10:02,770 --> 00:10:00,230
to compare with a natural appetite

269
00:10:04,600 --> 00:10:02,780
samples so going back here we've

270
00:10:05,950 --> 00:10:04,610
selected appetite specimens from three

271
00:10:08,950 --> 00:10:05,960
different geologic localities of

272
00:10:10,330 --> 00:10:08,960
neoproterozoic and Cambrian age so

273
00:10:12,700 --> 00:10:10,340
specifically we've looked at two

274
00:10:14,440 --> 00:10:12,710
phosphate localities so we've looked at

275
00:10:16,180 --> 00:10:14,450
samples from the late neopor to reserve

276
00:10:18,610 --> 00:10:16,190
through Shantou formations this is right

277
00:10:20,350 --> 00:10:18,620
before the boundary between the

278
00:10:22,000 --> 00:10:20,360
neoproterozoic and Cambrian and we also

279
00:10:24,670 --> 00:10:22,010
looked at the early cambrian shellac so

280
00:10:26,950 --> 00:10:24,680
formation of self cosmic Sun in addition

281
00:10:29,530 --> 00:10:26,960
to these two phosphate samples we also

282
00:10:31,300 --> 00:10:29,540
looked at a different one this is a this

283
00:10:33,610 --> 00:10:31,310
is a 15-mile group assist me

284
00:10:35,890 --> 00:10:33,620
neoproterozoic at the locality right at

285
00:10:37,900 --> 00:10:35,900
the Alaska Yukon border this is

286
00:10:40,660 --> 00:10:37,910
unrelated to foster it's actually sort

287
00:10:42,190 --> 00:10:40,670
of special this is the samples that I'll

288
00:10:44,050 --> 00:10:42,200
be talking about here have been

289
00:10:47,040 --> 00:10:44,060
interpreted to be really the earliest

290
00:10:49,630 --> 00:10:47,050
evidence of bio mineral apatite

291
00:10:52,150 --> 00:10:49,640
formation so these are fossil protists

292
00:10:53,410 --> 00:10:52,160
skeletal scales that are made of apatite

293
00:10:58,630 --> 00:10:53,420
so this is really fundamentally

294
00:10:59,890 --> 00:10:58,640
different than these two okay so to give

295
00:11:01,780 --> 00:10:59,900
you a better sense of what sorts of

296
00:11:03,070 --> 00:11:01,790
specimens we're looking at for the

297
00:11:05,580 --> 00:11:03,080
phosphorus would dushyant's from the

298
00:11:07,870 --> 00:11:05,590
chillax oh we looked at primarily at the

299
00:11:08,510 --> 00:11:07,880
apatite concreted wood so these are a

300
00:11:11,390 --> 00:11:08,520
little gray

301
00:11:12,920 --> 00:11:11,400
that chemically precipitated and Ryan's

302
00:11:15,440 --> 00:11:12,930
you get them now made of calcium

303
00:11:16,790 --> 00:11:15,450
carbonate say in the Bahamas and then we

304
00:11:19,400 --> 00:11:16,800
also looked at a variety of pure

305
00:11:21,740 --> 00:11:19,410
mineralized apatite fossils including

306
00:11:24,470 --> 00:11:21,750
sign of bacteria and animal embryos and

307
00:11:26,330 --> 00:11:24,480
here these are the fossils from the

308
00:11:28,760 --> 00:11:26,340
15-mile group so these have been

309
00:11:30,950 --> 00:11:28,770
interpreted as biologically controlled

310
00:11:33,470 --> 00:11:30,960
apatite mineralization from protists so

311
00:11:35,390 --> 00:11:33,480
these are these scale fossils um and I

312
00:11:37,040 --> 00:11:35,400
also want to mention that with all of

313
00:11:39,110 --> 00:11:37,050
these specimens they also carry with

314
00:11:41,060 --> 00:11:39,120
them a good deal of contextual geologic

315
00:11:43,280 --> 00:11:41,070
information so particularly with the

316
00:11:45,620 --> 00:11:43,290
phosphates we know that we're well

317
00:11:49,640 --> 00:11:45,630
constrained to a really shallow marine

318
00:11:51,590 --> 00:11:49,650
environment we know that apatite formed

319
00:11:54,020 --> 00:11:51,600
quite early potentially on the order of

320
00:11:55,700 --> 00:11:54,030
weeks fallen burial and then

321
00:11:57,980 --> 00:11:55,710
specifically for the phosphates we know

322
00:11:59,960 --> 00:11:57,990
we're sampling the shallow sediment

323
00:12:02,360 --> 00:11:59,970
deposition environment but in the case

324
00:12:04,100 --> 00:12:02,370
with a bio mineral learn step sampling

325
00:12:07,880 --> 00:12:04,110
kind of a lark column where the organism

326
00:12:10,160 --> 00:12:07,890
potentially lives in the past okay so we

327
00:12:12,590 --> 00:12:10,170
can also analyze these apatite specimens

328
00:12:14,420 --> 00:12:12,600
spectroscopically so here our average

329
00:12:17,330 --> 00:12:14,430
fluorescence spectra for each of these

330
00:12:19,670 --> 00:12:17,340
three geologic localities and so if we

331
00:12:21,530 --> 00:12:19,680
calculate them their associated ALP

332
00:12:23,510 --> 00:12:21,540
values but we get these are the three

333
00:12:25,820 --> 00:12:23,520
average aoki values for the three

334
00:12:27,770 --> 00:12:25,830
different localities and really the main

335
00:12:31,370 --> 00:12:27,780
takeaway here is that they all generally

336
00:12:33,620 --> 00:12:31,380
fall below a o P values of about 0.5 and

337
00:12:35,720 --> 00:12:33,630
so if we are to directly compare this to

338
00:12:38,960 --> 00:12:35,730
the experimental calibration curve we

339
00:12:41,830 --> 00:12:38,970
would then infer relatively low local

340
00:12:44,840 --> 00:12:41,840
oxygen in the surrounding environment

341
00:12:46,970 --> 00:12:44,850
but we do also see a relatively

342
00:12:49,730 --> 00:12:46,980
significant difference particularly with

343
00:12:51,350 --> 00:12:49,740
these two phosphate samples and so we

344
00:12:54,410 --> 00:12:51,360
could potentially interpret that as

345
00:12:55,850 --> 00:12:54,420
suggesting that the qu lacto sediment

346
00:12:57,650 --> 00:12:55,860
shallow sediment environment was

347
00:13:00,560 --> 00:12:57,660
potentially more oxygenated than that of

348
00:13:02,600 --> 00:13:00,570
the Santo and if we consider this

349
00:13:04,520 --> 00:13:02,610
history of increased oxygenation between

350
00:13:08,840 --> 00:13:04,530
the neoproterozoic and Cambrian this is

351
00:13:10,460 --> 00:13:08,850
relatively promising so finally I just

352
00:13:12,770 --> 00:13:10,470
want to mention these other apatite

353
00:13:14,450 --> 00:13:12,780
specimens which are unique to the chill

354
00:13:17,240 --> 00:13:14,460
act oh these are really beautifully

355
00:13:19,310 --> 00:13:17,250
preserved you he drill apatite crystals

356
00:13:22,249 --> 00:13:19,320
that are actually encrusting on the

357
00:13:24,859 --> 00:13:22,259
micro fossils themselves and so because

358
00:13:26,569 --> 00:13:24,869
it's a more well-organized crystalline

359
00:13:28,429 --> 00:13:26,579
form of apatite we can actually image

360
00:13:30,499 --> 00:13:28,439
them with decent resolution using

361
00:13:34,219 --> 00:13:30,509
fluorescence spectroscopic techniques

362
00:13:36,409 --> 00:13:34,229
and so maps here in green is the spatial

363
00:13:38,359 --> 00:13:36,419
distribution of these oxic related

364
00:13:40,009 --> 00:13:38,369
fluorescence signatures and in red is

365
00:13:43,009 --> 00:13:40,019
the spatial distribution of these an

366
00:13:45,679 --> 00:13:43,019
toxic associated fluorescence features

367
00:13:49,219 --> 00:13:45,689
so we see it this patterning where the

368
00:13:51,679 --> 00:13:49,229
crystal has this oxic core surrounded by

369
00:13:53,419 --> 00:13:51,689
an anoxic rind and we can do this three

370
00:13:56,090 --> 00:13:53,429
dimensionally and so you can see if we

371
00:13:58,759 --> 00:13:56,100
then rotate this and software and just

372
00:13:59,989 --> 00:13:58,769
cut through a slice down the center here

373
00:14:01,849 --> 00:13:59,999
and rotate it you can see that this

374
00:14:04,639 --> 00:14:01,859
patterning also continues with depth

375
00:14:07,819 --> 00:14:04,649
through the crystal we can do a point

376
00:14:10,609 --> 00:14:07,829
spectral transect from the interior to

377
00:14:12,949 --> 00:14:10,619
the exterior from a through e calculate

378
00:14:15,229 --> 00:14:12,959
the Associated AP values and we see that

379
00:14:16,909 --> 00:14:15,239
we get the same pattern of increased a

380
00:14:18,499 --> 00:14:16,919
row P values in the center indicating

381
00:14:21,109 --> 00:14:18,509
greater amounts of oxygen during the

382
00:14:23,629 --> 00:14:21,119
crystal formation and decreasing a hopi

383
00:14:26,449 --> 00:14:23,639
values through to the exterior and so

384
00:14:29,150 --> 00:14:26,459
this patterning is is very reminiscent

385
00:14:31,340 --> 00:14:29,160
of a well known phenomenon for crystal

386
00:14:32,599 --> 00:14:31,350
growth called concentric zonation and so

387
00:14:34,309 --> 00:14:32,609
what this happens is you get this

388
00:14:37,579 --> 00:14:34,319
chemical change as the crystal grows

389
00:14:39,439 --> 00:14:37,589
from the center to the outside and so if

390
00:14:41,689 --> 00:14:39,449
that is the case and potentially this

391
00:14:43,789 --> 00:14:41,699
donation pattern is indicative of

392
00:14:45,590 --> 00:14:43,799
increasing local anoxia during crystal

393
00:14:49,369 --> 00:14:45,600
growth and phosphor eye burial and this

394
00:14:51,349 --> 00:14:49,379
makes a good deal with them okay so as I

395
00:14:53,569 --> 00:14:51,359
come to a close I just do want to

396
00:14:55,909 --> 00:14:53,579
mention an important caveat which is

397
00:14:58,069 --> 00:14:55,919
probably the most obvious which is that

398
00:15:00,169 --> 00:14:58,079
our experimental heat substituted

399
00:15:01,939 --> 00:15:00,179
apatite is perhaps not absolutely

400
00:15:04,309 --> 00:15:01,949
directly analogous to aqueous

401
00:15:07,249 --> 00:15:04,319
precipitation of apatite in a marine

402
00:15:09,379 --> 00:15:07,259
environment but I do want to mention we

403
00:15:10,939 --> 00:15:09,389
would argue that really the oxygen

404
00:15:13,340 --> 00:15:10,949
dependent mechanism that we're tracking

405
00:15:15,649 --> 00:15:13,350
here isn't very inherent to the apatite

406
00:15:17,090 --> 00:15:15,659
structure itself in this apatite these

407
00:15:19,639 --> 00:15:17,100
features of the apatite structure are

408
00:15:21,739 --> 00:15:19,649
constant regardless and so we still see

409
00:15:23,629 --> 00:15:21,749
the strong potential for increased

410
00:15:25,849 --> 00:15:23,639
quantitative refinement of this paleo

411
00:15:28,489 --> 00:15:25,859
barometer whether or not the actual

412
00:15:31,879 --> 00:15:28,499
specific scaling of these AOP values and

413
00:15:33,859 --> 00:15:31,889
oxygen remain exactly the same and so

414
00:15:34,650 --> 00:15:33,869
moving forward what we really need to

415
00:15:36,809 --> 00:15:34,660
see

416
00:15:38,639 --> 00:15:36,819
similar oxygen controlled experiments

417
00:15:40,379 --> 00:15:38,649
that instead of doing this heat

418
00:15:44,129 --> 00:15:40,389
substitution we have actual aqueous

419
00:15:46,410 --> 00:15:44,139
precipitation and so with that we would

420
00:15:48,829 --> 00:15:46,420
then be able to more directly relate a

421
00:15:50,009 --> 00:15:48,839
or P values to local dissolved oxygen

422
00:15:53,129 --> 00:15:50,019
concentrations

423
00:15:55,050 --> 00:15:53,139
I also want to mention which is also

424
00:15:57,090 --> 00:15:55,060
exciting is that samarium which we

425
00:15:58,530 --> 00:15:57,100
focused on here is not the only rare

426
00:16:00,240 --> 00:15:58,540
earth element that has been suggested to

427
00:16:02,460 --> 00:16:00,250
be related to these oxygen dependent

428
00:16:04,410 --> 00:16:02,470
mechanisms for that incorporation into

429
00:16:06,509 --> 00:16:04,420
apatite so you know you could

430
00:16:07,800 --> 00:16:06,519
potentially envision an entire suite of

431
00:16:09,389 --> 00:16:07,810
rare earth elements that are each

432
00:16:12,809 --> 00:16:09,399
through their fluorescence signatures

433
00:16:14,819 --> 00:16:12,819
independently corroborating these oxygen

434
00:16:16,170 --> 00:16:14,829
related signatures and finally as I

435
00:16:18,749 --> 00:16:16,180
showed in that map there are numerous

436
00:16:21,090 --> 00:16:18,759
other phosphates of varying age leading

437
00:16:22,379 --> 00:16:21,100
up through the neoproterozoic membrane

438
00:16:25,319 --> 00:16:22,389
and oxygenation this so there are

439
00:16:29,280 --> 00:16:25,329
potentially a whole slew of samples to

440
00:16:30,540 --> 00:16:29,290
apply these these procedures - okay so

441
00:16:32,189 --> 00:16:30,550
with that I'm just going to leave these

442
00:16:33,689 --> 00:16:32,199
very broad conclusions up here and I'll

443
00:16:43,019 --> 00:16:33,699
be happy to take any questions so thank

444
00:16:50,400 --> 00:16:43,029
you very much Thank You Amanda any

445
00:16:51,600 --> 00:16:50,410
questions thank you for that like it was

446
00:16:53,280 --> 00:16:51,610
really cool yeah

447
00:16:54,809 --> 00:16:53,290
I was just wondering have you been able

448
00:16:56,550 --> 00:16:54,819
to look at the zonation in modern

449
00:16:59,460 --> 00:16:56,560
samples that you can actually control

450
00:17:00,269 --> 00:16:59,470
the oxygen amounts of to see if they

451
00:17:01,829 --> 00:17:00,279
also occur

452
00:17:03,689 --> 00:17:01,839
yeah we would we would like to look at

453
00:17:11,809 --> 00:17:03,699
modern samples unfortunately we haven't