1. Snowball Earth vs. Slushball Earth..

2. In 1960s, studies showed that significant
Early Evidence
In 1960s, studies showed that significant
glacial deposits of age million years are
on nearly every continent
1970s: When sediments form magnetic minerals point
to the N pole. At the equator they will point horizontally at the equator. Found that glacial rocks million years ago had horizontal magnetic properties indicating low latittude glaciation.
1980s climate modeling show the plausibility that
ice-albedo feedback caused instability in climate

3. Ice-Albedo Feedback; Albedo is % of sunlight that is reflected by some surface.
As Earth cools:
1. Ice forms at lower and lower latitudes
2. Albedo rises
3. Reflects more solar radiation
4. Cools even more
(positive feedback loop)
Once ice formed at a critical latitude (30˚)
the positive feedback so strong that T plummets
Creates a completely frozen planet. (snowball earth  slushball earth means equatorial surface ocean not frozen)
Geothermal heat keeps oceans from freezing completely, so ice 1km thick on average.
Albedo:
0.1 seawater
0.3 bare land
0.6 sea ice
0.9 fresh snow

4. A Permanent Catastrophe?
Would have already extinguished life.
Temperatures would have been -50˚C.
No means of escape.
In 1977:
Discovery of hydrothermal vents.
Discovery of dry valleys of Antarctica -
organisms can live in extremely cold environments.
Appreciation for life in extreme environments.
Extremophiles

5. Extremophiles
Extremophiles provide evidence that life could have persisted under snowball Earth conditions.

6. How To Reverse a Snowball Event?
In late 1980’s, Joe Kirschvink of CalTech
Gave it the name Snowball Earth.
Showed that the CO2 supply would continue
BUT it would be so cold that there is no liquid water
at the surface.
Weathering reactions stop, sloooooow dooooowwwwn.
What happens then?

7. How To Reverse a Snowball Event?
Estimated 300x present level of CO2 needed to overcome the albedo
of the Snowball Earth.
Would have taken several million years for this much CO2 to
accumulate by natural means.
There is some evidence of high tectonic activity and vulcanism which would aid in building up the CO2
CO2 causes warming, which begins melting.
Melting would have been catastrophic - sea ice gone in few hundred years.
Sea level rises dramatically!
As soon as the ice is gone, it gets rapidly hot!!

8. The Following Hot House
After the Snowball, now have a hot house.
How hot?
50˚C!!
Have a CO2-rich atmosphere, warm conditions.
What happens next??

9. The Carbon removal cycle Kicks Into High Gear!
The CO2 rich atmosphere would have again dissolved in the rain and turn into carbonic acid – similar to what happens during the first 500 million years of Earth’s history.
Extremely Acidic rain would have been present.
Bottom line: for about a million year period, the surface of the Earth was tremendously inhospitable for life as it was
Cold and frozen
Then extremely hot (about degrees F)
Then had long period of extremely acid rain
Extremophile microbes likely are the mechanism that keeps life going on the Earth under these extreme conditions.