4.2 Transition from microbial to macrobial life: Snowball Earth and the Ediacara Biota - Part 2 - Svend Stouge

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Origins - Formation of the Universe, Solar System, Earth and Life

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University of Copenhagen

Origins - Formation of the Universe, Solar System, Earth and Life

372 ratings

The Origins course tracks the origin of all things – from the Big Bang to the origin of the Solar System and the Earth. The course follows the evolution of life on our planet through deep geological time to present life forms.

From the lesson

Transition from Microbial to Macrobial Life: Snowball Earth and the Ediacara Biota / Eukaryotic Evolution and the Phylogeny of All Life

In this module, we take a closer look at how the physical and biological conditions that made the Cambrian Explosion possible arose. In the first lectures Svend Stouge will tell you about the dramatic consequences of climate changes seen toward the end of the Precambrian. Geological evidence supports the idea that the Earth was completely covered in ice during periods that we, for obvious reasons, refer to as Snowball Earth. In the remaining lectures Martin Sørensen will tell you about one of the most significant building blocks of life on Earth – the cell – and how the early bacterial cells evolved and became capable of forming the huge variety of life that we see today. Martin Sørensen will also show how different evolutionary trends of cells resulted in six major organism groups, of which several gave rise to multicellular life.

4.1 Transition from microbial to macrobial life: Snowball Earth and the Ediacara Biota - Part 1 - Svend Stouge19:43

4.2 Transition from microbial to macrobial life: Snowball Earth and the Ediacara Biota - Part 2 - Svend Stouge13:47

4.3 Eukaryotic Evolution and the Phylogeny of All Life - The Transition from the Prokaryotic to the Eukaryotic Cell and the Endosymbiont Theory - Martin V. Sørensen11:48

4.4 Eukaryotic Evolution and the Phylogeny of All Life - The Eukaryotic Tree of Life and the Six Super Kingdoms: Archaeplastida - Martin V. Sørensen7:26

4.5 Eukaryotic Evolution and the Phylogeny of All Life - The Six Super Kingdoms: Excavata and Rhizaria - Martin V. Sørensen7:03

4.6 Eukaryotic Evolution and the Phylogeny of All Life - The Six Super Kingdoms: Chromalveolata - Martin V. Sørensen5:56

4.7 Eukaryotic Evolution and the Phylogeny of All Life - The Six Super Kingdoms: Amoebozoa and Opisthokonta - Martin V. Sørensen 7:06

Meet the Instructors

Henning Haack
Associate Professor
Natural History Museum
James Connelly
Professor
Natural History Museum of Denmark
Vivi Vajda
Professor
Department of Geology, Lund University
Jon Fjeldså
Professor, Curator
Thomas Gilbert
Professor
Michael Houmark-Nielsen
Associate Professor
Natural History Museum of Denmark
Bent Erik Kramer Lindow
Curator
Natural History Museum of Denmark
Gilles Guy Roger Cuny
Associate Professor
Natural History Museum of Denmark
Ole Seberg
Associate Professor
Natural History Museum of Denmark
Gitte Petersen
Associate Professor
Natural History Museum of Denmark
Tais Wittchen Dahl
Assistant Professor of Geobiology
Arne Thorshøj Nielsen
Associate Professor
Natural History Museum of Copenhagen
Martin Vinther Sørensen
Associate Professor, Curator
Natural History Museum of Denmark
Svend Stouge
Associate Professor
Natural History Museum of Denmark
Danny Eibye Jacobsen
Associate Professor, Curator
Natural History Museum of Denmark
Jan Audun Rasmussen
Associate Professor
Natural History Museum of Denmark
Emily Catherine Pope
Assistant professor
Natural History Museum of Denmark

[MUSIC]

Hello again.

In this second part, we will look at the mechanism and

the conditions that are important for the Snowball Earth.

There is a mechanism in favor of Snowball Earth, and

some required conditions includes the Fainter sun idea.

And we have a global oxygen event, I've mentioned that in the former part.

And then we have a global ice cover, of course is important.

And then we have talking about weathering and erosion shut down.

I mentioned that a little bit before, but we take it again.

And then the breakup of equatorial supercontinent,

which is about 770 million years before now.

Now if you look at the Faint sun, the presence of glacial deposits in the early

part of earth history is possible, because of a less radiant young sun.

It's only about 80% of the power as it is today.

So in the Fainter sun would have emitted like six percent less radiation in

the Neoproterozoic, and is considered as an important factor for

the cooling conditions.

Another thing is that you probably already know that,

when you go out in the snow, you can get sun in the eyes, so

we call that Albedo, that fresh snow can reflect lots of light, and

especially sunlight hitting a snow covered surface on earth.

You would get the sun rays would go back into space without heating anything.

And this is also a good condition for starting a Snowball Earth,

because there will be starting a little cooling mechanism that will

result in an increase of the earth covers of snow and ice.

Now, in the increase of the earth's covers of snow and ice, would in turn increase

the earth's Albedo, which would result in the positive feedback for cooling.

If you have enough snow and ice accumulate,

then runaway cooling would result.

This positive feedback is facilitated by the equatorial continental distribution.

Which would allow ice to accumulate in regions closer to

the equator where solar radiation is most direct.

Another idea in support for this Snowball Earth creation or event,

is that the person called Williams in 1975 he proposed actually,

that the angle between the Earth's spin axis and

the light like this, it would be much greater in the past.

So it means that it was deeply tilted up to about 54 degrees,

and that has to do at when you go into a cool period.

That means the equatorial regions would have been preferably glaciate and

subject to season temperature fluctuations.

The proposed high obliquity state in Earths early history,

may have been a result from the huge impact that produced the Moon,

in the very early days of the history.

If you look at the oxygen change through time,

the free oxygen formed by the activities bacteria, the oxygen came from

photosynthesis by this bacteria, and they provide the free oxygen to the atmosphere.

This was a disaster for some of the anoxic depending organisms such

as sulfur depending prokaryotes, which are the single cellular organisms.

Whereas others evolved and took advantage of this new source of energy.

That means the eukaryotes, which are one celled organism now with a nucleus.

At the same time a lull in the volcanic activity has been recorded with this

result, that the CO2 in the atmosphere was relatively low in that period.

The find result of a photosynthesis was that free oxygen removed,

atmospheric me10, which is a very acid greenhouse gas, much more active than CO2.

And closed up and

used up the carbon dioxide, which is another known greenhouse gas.

And this caused the temperature to crash and conditions for

a Snowball Earth was created.

Now, the end.

During this very cooling event, there's no evaporation and no rain during glaciation.

And without any rain but the volcanoes continue to erupt,

CO2 accumulates in the atmosphere.

The Earth is warming up.

At the ten percent CO2, abrupt warming begins.

Let's say they go from minus 50 degrees Celsius,

to about plus 50 degrees Celsius in a period about 10,000 years.

And because volcanoes under the ice,

which is, you can see if we know it from Iceland, they are continuing.

They are not concerning about ice or not ice.

They are still moving.

Since the earth was almost completely covered by ice,

carbon dioxide would not be risen from the atmosphere by release of

Alkali Metal Ions, weathering out the felicitous rocks.

Move forward to 30 million years, enough CO2 and methane,

mainly emitted from volcanoes, would accumulate to finally cause enough

greenhouse effect to make surface ice melt in the tropics,

until a band of permanently ice free land and water developed.

This would be darker than the ice and thus absorb more energy from the sun,

initiating a positive feedback.

On the continent, the melting of glaciers would release massive amount of

glacial deposits, which would erode and wither.

This positive feedback loop would melt the ice in the geological short order,

perhaps less than 1000 years.

Replacement of atmosphere's oxygen and depletion of CO2 levels,

would take further 1,000 years approximately.

This stabilization of substantial departures of me10 hydrates,

locked up in the low latitude permafrost, may also have acted as a trigger, and or

strung positive feedback for the deep glaciations and warming.

Now, if you look at all this evidence we have now been outlining, you can

have a little scenario, showing how the whole Snowball Earth scenario occurred.

Let us imagine that the Earth did change from normal climate to a snowball state,

or as a white planet and back again, using one or

several of these triggers mentioned before.

And how will that be like?

Well, the scenario starts with the polar icecaps.

And they will become larger and move towards the equator.

This will lead to a complete coverage of the Earth by ice, and

now leading to a Snowball Earth.

Now the CO2 communication with the ocean has stopped.

Ice cover is prohibiting the exchange between the oceanic atmosphere.

However, volcanic activity will continue, and

methane and carbon dioxide will build up in the atmosphere.

The greenhouse effect will reach a trace hold, and the ice will melt fast and

result in a hot house Earth and deposition the cap carbonate.

After the ice has melted the CO2 cycle starts again,

in turning the Earth into a normal tempered blue planet when seen from space.

So, this is the history about the actual event and

scenario that could occur from a Snowball Earth.

However, this kind of extreme conditions, how would we survive the life?

I mean, we are here, so

somehow life would survive even though it's a totally deep freeze.

But there's similar possibilities.

One is what we refer to as a Refugium.

Refugium is like a place where you can live, survive under hard condition.

In this case, it could be a crack under ice which might be a potential refugium

and is all survivors spot for

organisms which are doing photosynthesis during a snowball event.

But another one which is very unusual for us,

is the discoveries that is recently found is the life condition at the ocean floor,

and that may give you another insight in alternative survivors.

If you look at what they called smokers, a black smoker, this is a type of

hydrothermal vent, where you have very, what for us very harsh conditions.

First of all, down the ocean bottom there's a high pressure.

There's no oxygen, there's no light.

There's a high temperature,

because this is coming out from the hot gas from below the sea bottom.

In reservoirs, we have anaerobic and no oxygen life.

And is powered by chemicals in deep ocean hydro firmaments surviving in

Earth's deep oceans.

And the most important thing for that is sulfur.

If you look at the noxious sulfur is the prime energy supplier for life.

As I said, no light, no oxygen and no photosynthesis is possible.

So here we have a very harsh situation where you have high versus cold

temperature almost like a thin wall, and still you have lots of organisms down

there despite this extreme, adverse, unpleasant, or impossible conditions.

When there's a high diverse examples is presently living around these smokers.

Now, if we look at what happens, so where there's three true possibilities can be

considered for survival of life during the hot core snowball earth events.

If you look at the following after the snowball, what the implication has.

When the melting the ice may have presented many new opportunities for

diversification, and

may indeed have driven the rapid evolution which to place at the Cryogenian period.

After the snow disappeared, sediment supplied to the ocean would be light in

nutrition, such as phosphor, which combined with the abundance of CO2,

would trigger a Cyanobacterial population explosion.

Which would cause a relative rapid reoxygenation of the atmosphere.

Which may have contributed to the rise of a well known Ediacaran biota and

subsequent Cambrian explosion.

A higher oxygen concentration allowing large multi cellular life forms to

develop.

That's one reaction, perhaps.

The snowball episode of a Huronian/Makganyene glaciation which

went for 2,400 million years ago.

And the snowball of between 580 to 850 million years,

in which itself has a number of distinguished episodes thought to be

caused by the evolution of oxygenic photosynthesis, and then the rise of more

advanced, multi cellular animal life and life colonizations of the land.

So, if you have a look around, considering these unusual situations,

do we have any candidate outside the Earth, like in space.

The answer is sure not, but one of the moons around Jupiter shows some

interesting features that resembles the living, so to speak, Snowball Earth.

Europa is about the same size as the moon, but big enough so

Galileo actually saw it already in 1610.

The surface of Europa is made by ice.

It's considered to have water below the surface, which may support life.

So there is an actual living copy,

example of a Snowball Earth, at the moment out in space.

Now we're always concerned about the future,

could a snowball event happen again?

Could the glaciation, hard core glaciation occur again?

The last one we had occurred in late Precambrian.

We also had following glaciations younger than this, but

they did not reach to a low latitude, and no one was coming to the equator.

But we had glaciation.

So to speak about the possibility of a new Snowball Earth, then we could say, no.

Because we're following the steadily increasing, solar luminosity, and

also the present continental configuration will conspire against it.

But, yes if you believe in a last asteroid hits the Earth,

then it could trigger a snowball because the ocean is relatively cold.

Or if the Wilson cycle of continent distribution of super continents

are important, then perhaps in about 200 million years from now, it might happen.

Now I have some final comments.

Significant, widely spread the idea [INAUDIBLE] made

the glaciation that occurred in the pre-Cambrian.

There are some conflicts in their interpretations of the rocks.

Snowball Earth or Slushball?

Slushball means that it's not completely frozen down,

but there might have been areas where they're open.

Then we have the break up of supercontinents.

There are some disagreement whether this actually are associated with

Snowball Earth.

Because these models are not fully accepted.

So, to finish off here, the debate is still going on.

Thank you very much for your attention.

[MUSIC]

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