When bivalves ruled the world(low levels of oxygen do much more than t...)

The hypothesis unfolds like this: High C02 levels would have increased temperatures, resulting in global warming on a large scale. With no cold water at the poles, ocean circulation would have stagnated. The oceans would have become low in oxygen, killing off life in deeper waters where there was no opportunity for water to mix with the little oxygen in the atmosphere.

More carbon dioxide would have been created as life forms died and microbes broke them down, which also would have created poisonous hydrogen sulfide. The oceans would have become an inhabitable chemical cocktail.

Follow the CO2 In fact, there have been many CO2 events in geologic time, and theyve literally left their mark.

You can see where the rock turned dark, says Fraiser, pointing out different-colored layers in a fossil samples from the period. That is an indicator of low oxygen at the time. These are from sites that were underwater at the beginning of the Triassic period.

Fraiser, who has just finished her first year at UWM, is one of several new faculty in geosciences and its emerging paleobiology program.

She has collected fossil samples of the marine survivors from the period in what today are China, Japan, Italy and the western United States. The similarities of the fossils from all these locations have been surprising.

It is unexpected to see that, says Fraiser. It appears that these bivalves and gastropods were the only survivors worldwide.

They had all the right characteristics to tolerate the lack of oxygen, she says. They were tiny, shallow-water dwellers, with a high metabolism and flat shape that allowed them to spread out to extract more of the limited oxygen when feeding.

Toxic conditions also inhibited marine life from producing a shell. Size suddenly mattered for mollusks, and only the very small survived, eroding the balance of the marine food chain.
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