reading: Chapter 4 Lecture 25. Snowball Earth vs. Slushball Earth..

In 1964, Brian Harland at Cambridge Univ. noticed Neoproterozoic glacial deposits were widely distributed on nearly every continent Geologic evidence suggested glaciation at low latitudes Mikhail Budyko at Leningrad Geophysical Observatory worked on climate modeling discovered that ice-albedo feedback caused instability in climate Early Observations

Ice-Albedo Feedback 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. 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

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. also: “discovery” of plate tectonics

Evidence of Glaciation Glaciers carry large stones - when the glaciers melt, they leave dropstones. Characteristic of glaciers.

Glaciation at Low Latitudes (Near Equator) Paleomagnetism When sediments form magnetic minerals point to the N pole. At the equator they will point horizontally at the equator. Found that glacial rocks in the Neoproterozoic had horizontal magnetic properties. Suggests glacial deposits occurred at low latitudes.

Other Evidence of Large Scale Change The return of banded iron formation in marine waters What do you need have have BIF? Lots of Fe 2+ - Little O 2 Suggests oceans cut off from the atmosphere - ice??

Other Evidence of Large Scale Change, cont.

When Do We Have BIF?

How To Reverse a Snowball Event? In late 1980’s, Joe Kirschvink of CalTech Gave it the name Snowball Earth. Showed that the CO 2 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?

Estimated 350x present level of CO 2 needed to overcome the albedo of the Snowball Earth. Would have taken several million years for this much CO 2 to accumulate. CO 2 causes warming, which begins melting. As melting occurs what happens to the albedo? What does this do? 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 hot!! How To Reverse a Snowball Event?

The Following Hot House After the Snowball, now have a hot house. How hot? 50˚C!! Have a CO 2 -rich atmosphere, warm conditions. What happens next??

The Carbonate-Silicate Cycle Kicks Into High Gear! 1.CO 2 outgassing from volcanoes (greenhouse gas) 2.CO 2 dissolves in rain, lakes, streams, turns into carbonic acid 3.Carbonic acid reacts with rocks, making ions, quartz, and clay 4.Ions and dissolved CO 2 reacts to make carbonate rocks 5.Carbonate rocks are subducted 6.Subducted carbonate rocks turned into CO 2 Extremely acidic rain. Rapid weathering of rocks. Since it is warm, we should make _____________ carbonate rocks.

Evidence of a Hot House Huge, thick carbonate rock over layers of glacial deposits - called cap carbonates - is evidence that they were formed very rapidly - few hundred yrs

Snowball Earths During Critical Geologic Times ~2.3 Ga - right as oxygen becomes present in the atmosphere 3 or 4 glacial events within a relatively short period of time. Neoproterozoic - animal embryo and early sponges in between glacial events. Thought to be 3 glacial events. Both are associated with increases in oxygen.

Why Only One Snowball Event on the Early Earth? Faint Young Sun - expect more glacial events in the Archean and Paleoproterozoic! 1.Geologic evidence of an early CO 2 -rich atmosphere 2.Also evidence for an early CH 4 -rich atmosphere 3.CH 4 is easily oxidized to CO 2 4.But CH 4 is a stronger greenhouse gas 5.Oxygen in the atmosphere destroyed the CH 4 greenhouse 6.Catastrophic entrance into a Snowball episode

reading: none - budget documents on the web site Lecture 26. Exploration, the Federal and NASA Budgets, and Politics.