The greenhouse effect likely saved primitive life from extinction on a frigid "Snowball Earth" 700 million years ago, a University of Toronto expert in ancient climate concludes in research published today.
And that set the stage for the eventual explosion of species that produced today's world, says Richard Peltier, a professor of atmospheric physics.
Peltier says carbon dioxide produced from the decay of minute organic particles in the oceans warmed the ancient atmosphere enough to prevent the entire planet from being covered with massive sheets of ice, a controversial theory dubbed Snowball Earth when it was first proposed a decade ago.
"The biosphere defended itself against a hard-snowball catastrophe. The planet was actually closer to a slushball than a snowball," he said. The researcher also pointed to a parallel between the Slushball Earth period and the past 150 years. In both cases the biosphere was controlling the climate, back then through the decay of organic particles in the ocean and today through carbon dioxide emitted by human activities.
For the rest of the world's life, the reverse has been true, with the climate controlling the biosphere, Peltier said.
But the leading proponent of Snowball Earth, Toronto-born Harvard geologist Paul Hoffman, dismissed this latest version of the slushball concept as "implausible."
"It's kind of like a miracle solution," he said in an interview.
The slushball-snowball debate is crucial to understanding how life evolved on Earth. Somehow primitive life such as algae and bacteria survived intense cycles of glaciation spread over 200 million years to allow the first fernlike animals to emerge 575 million years ago. These were followed 30 million years later by the Cambrian explosion of much more complex species that led to today's biodiversity, humans included.
The Snowball Earth theory has sparked intense debate among scientists since 1998, when it was popularized by Hoffman, who had been with the Geological Survey of Canada. Many biologists argue that evidence points to some normal biological activity continuing even during the height of glaciation in the period from 850 to 630 million years ago. That wouldn't have been possible with kilometre-thick ice covering the oceans.
Another leading expert in ancient climate mocked what he called these "yo-yo" scenarios, with the planet supposedly flipping back and forth between super ice houses and super greenhouses.
"The glaciations were harsh, but that does not justify piling up special pleadings on special pleadings just to make the tail wag the dog," emailed University of Ottawa professor Jan Veizer, a Fulbright Fellow at the California Institute of Technology.
Peltier reconstructed the Earth's ancient climate by combining two sophisticated computer models.
Working with PhD student Yonggang Liu and undergraduate John Crowley, the U of T professor fed the computer model a version of Earth in which the oceans harboured a hundred times higher levels of organic particles than they currently contain. His theory held that the oceans had stored vast amounts of organic material because the Earth was cooling.
But as the planet headed for the deep freeze, the laws of chemistry and physics pushed the oceans to emit vast amounts of carbon dioxide, the gas chiefly responsible for global warming. Peltier said this led to large open patches of water near the equator where primitive aquatic plants could still carry out crucial photosynthesis, which uses energy from sunlight to make food.
