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[Music]

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good afternoon my name is Jennifer I am

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a paleo biologist and a research fellow

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here at LC and also at University of

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Cambridge in the UK and I'd like to talk

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to you now about the evolutionary origin

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of the animals including us

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so the eon of time which we live in

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today it's called the phanerozoic this

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means visible life or literally visible

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animals

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this began 541 million years ago in the

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Cambrian period this is the time when

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many of the modern animal groups first

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appear in the fossil record you can see

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some examples of these up here so this

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is a time when there was a great

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increase in the diversity of life and

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this is called the Cambrian explosion so

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what led to the Cambrian explosion

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why did this happen at that time to

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understand this we need to look back at

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the geological record of life just

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before this in the proterozoic eon

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meaning earlier life at this time the

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planet was quite different from that of

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today levels of oxygen in the atmosphere

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and the oceans began to rise from

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initially very low levels and the oceans

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may still have been quite toxic to

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modern animals with very low levels of

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oxygen and high levels of iron and

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sulfur life forms were still microscopic

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such as photosynthetic cyanobacteria

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whose colonies form mounds called

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stromatolites at the edge of the sea but

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at this time no plants or animals were

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yet living on the land so let's

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a closer look at life in the proterozoic

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eon this is a microfossil very small

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fossil called Fangio morpha this is

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thought to be a type of red algae and so

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a relative of plants and this is from

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around 1.2 billion years ago fossils

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like man geomorphic show that life forms

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had already evolved multicellularity

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many cells in their body by this time

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but they were still very small for

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example

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Mangiamo fur was less than one

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millimeter long and very thin

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later in the Proterozoic we have a

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geological period called the cryogenian

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which means cold birth during this time

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the planet experienced some of the

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greatest changes in climate but has ever

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had in its history there were at least

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two massive glaciations ice ages that

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covered much of the surface of the

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planet in ice and each lasted for

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millions of years these glaciations were

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so severe that they are called snowball

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earth events these may have restricted

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the abundance of many life forms

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including the photosynthetic

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microorganisms which produce oxygen and

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form the base of the food chain for

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everything else but life survived the

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snowball earth events and there are

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fossils from the cryogenian period

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these include mysterious circles in the

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rock such as the twitcher discs which

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are from the Twitter rock formation in

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lymph Kensie mountains from Canada these

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are around one centimeter wide and they

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may perhaps be simple relatives of

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animals but this simplicity may

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that they could instead be colonies of

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microorganisms rather bacteria or

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microalgae and not animals at all as

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well as fossils of animal and plant

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bodies ancient rocks can also preserve

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molecular fossils these are also known

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as biomarkers these are molecules which

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are known to be produced by living

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groups such as animals like sponges

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sponge biomarkers like this molecule

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here have been found in cryogenian rocks

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which are more than 635 million years

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old

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this suggests that sponges which are the

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most ancient of the living animals had

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evolved by this time so where are they

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in the fossil record this tiny fossil is

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less than one millimeter wide yet it is

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similar in shape to simple sponges that

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are still alive today with a central

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opening like those you can see here

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which may have functioned to draw

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through water as it fed on small

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particles from the water flow this could

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suggest that sponges had indeed evolved

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by this time that the animals had begun

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to diversify but they were still mostly

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very small and so very rare to fossilize

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at the end of the snowball earth events

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we enter a new geological period the

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Ediacaran period running from 635

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million years ago up to the Cambrian

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boundary at 541 million years ago during

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this time the earth became more

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hospitable to animals with a warmer

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climate and potentially an increase in

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the above

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of microorganisms those microorganisms

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that produce oxygen as well as food for

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animals some Ediacaran rocks such as

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these from Newfoundland Canada show

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changes in color from red to grey that

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are due to changes in the chemistry of

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iron in the rock this shows that at

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least here at this time there were

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increases in the level of oxygen so

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there is another rise in the amount of

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oxygen in the ocean right at this time

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this increase in oxygen may have allowed

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life forms such as early animals to

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reach large size to grow to new sizes

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not seen in life before this is because

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large animals like us need lots of

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oxygen in order to gain energy from our

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food by respiration from this time a

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wide range of large life forms appear in

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the fossil record these are known as the

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Ediacaran biota some of these look a

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little like living animals like this

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fossil creature called Spragg ina at the

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bottom here others look more unusual

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such as these rangaiah moths the group

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which I work on myself

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these had bodies that were made up of

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many small branches this type of shape

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is known as a fractal meaning broken

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shape and this reconstruction here was

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computer generated using a fractal

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algorithm Rangi moths are named after a

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fossil could rangayya which you can see

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in this example here with exceptionally

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preserved branches rangaiah was

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discovered in namibia africa in the

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early 20th century among the rocks of

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this beautiful but dry landscape

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geologically

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these fossils from Namibia are among the

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younger members of the Ediacaran biota

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the very oldest of these large Ediacaran

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fossils are found in Newfoundland Canada

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such as these beds of fossils at

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mistaken point which is now a world

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heritage site these beds are covered in

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fossils which you can see here as pale

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lines all over the rock if we look in

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close up at some of these fossils from

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Newfoundland we can see that here

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Ediacaran fossils are preserved as faint

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impressions on the surface of the rock

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some of these are really very large such

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as this fossil called Tripathy which is

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a few centimetres wide but more than one

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metre long extending like a ribbon along

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the rock among these strange forms are

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some others which look more like living

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animals such as this triangular fossil

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with in here called effect Ardis this

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may be an impression of a simple sponge

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of a similar shape to the ones we see

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today the Ediacaran period is named

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after another important fossil site in

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the ediacara hills of south australia

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Ediacaran fossils from australia include

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other mysterious types such as this

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large fossil called Dickon Sonja with

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many fine branches or segments as well

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as others like this small fossil here

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called Pavan Khurana which is the shape

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of the English letter T rocks from

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Australia preserved the transition all

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the way through the Ediacaran to the

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Cambrian among these fossils are small

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burrows which show the traces of

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movement on and through the sediment of

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the sea floor these fossils show that by

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the late edie Akron active

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moving animals had evolved as we move

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into the Cambrian period worldwide we

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see many more fossils of active moving

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animals such as this fossil called gali

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octina which looks very similar to

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modern tena fours also known as comb

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jellies this fossil is from Chang Jiang

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in China a famous place where

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exceptional fossils of soft bodied

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animals like this can be found although

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these are otherwise rare in the fossil

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record another place where exceptional

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Cambrian fossils have been found is the

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Burgess Shale in the Canadian Rocky

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Mountains these fossils include

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relatives of modern arthropods the group

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which includes shrimp crabs and insects

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today these fossils include this large

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predator called anomalocaris this

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dangerous animal was up to a meter long

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and had huge claws in front of its mouth

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for catching prey what was it eating

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well among Cambrian fossils are also

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small fish like animals such as this

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fossil from the Burgess Shale called

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pacaya the kaya was an active swimming

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animal with a head that had sense organs

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and a nerve cord which ran along its

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back these features show that pacaya was

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a distant relative of vertebrates

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animals with backbones like us fossils

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like pacaya tell us that some of the

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most important human features like our

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brain have evolutionary origins among

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very early animals of the Cambrian more

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[Applause]

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[Music]