Snowball fight erupts over frozen Earth theory

Snowball fight
However, Schrag argued that the fossil record is "terrible" from the Cryogenian period, so scientists don't actually know whether the business of life was disrupted or not. What is more certain is that a major evolutionary event—the appearance of multicellular animals—occurred a few million years after all the ice melted.

Schrag doesn't think this was a coincidence.

Moreover, he believes that Allen and others have a simplified "cartoon" picture of the snowball Earth that they use to attack it.

"The model is much more dynamic than they assume," Schrag said.

It is wrong, according to Schrag, to say that no water would be around during a Snowball Earth. Greenhouse gases emitted by volcanoes would warm the planet enough for puddles to form near the equator, and geothermal vents would create ice-free oases where life could survive.

Handle with care?
Even though the debate over Snowball Earth will continue, it raises the question of how bad climate change can get. Allen, for one, believes that natural brakes exist to prevent the climate from snowballing out of control.

"The Earth is not fragile," Allen said. "It has seen many bizarre climate extremes but always rebuilds itself afterwards."

He imagines that some sort of negative feedback mechanism — perhaps provided by primitive life forms — turned on during the Cryogenian period to keep the oceans from freezing.

Might there be another negative feedback mechanism to slow down current global warming?

"You are either brave or stupid to rely on that," Allen said.

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