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[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.
4:18
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.
5:32
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.
6:18
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.
6:58
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.
8:31
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.
9:54
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.
10:30
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.
11:14
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.
12:01
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]
Henning HaackAssociate Professor
James ConnellyProfessor
Vivi VajdaProfessor
Jon FjeldsåProfessor, Curator
Thomas GilbertProfessor
Michael Houmark-NielsenAssociate Professor
Bent Erik Kramer LindowCurator
Gilles Guy Roger CunyAssociate Professor
Ole SebergAssociate Professor
Gitte PetersenAssociate Professor
Tais Wittchen DahlAssistant Professor of Geobiology
Arne Thorshøj NielsenAssociate Professor
Martin Vinther SørensenAssociate Professor, Curator
Svend StougeAssociate Professor
Danny Eibye JacobsenAssociate Professor, Curator
Jan Audun RasmussenAssociate Professor
Emily Catherine PopeAssistant professor
