Article Posted on : - Dec 23, 2008

An artist's impression of fully frozen Earth of ancient times.

LONDON (BNS): Carbon dioxide, the main ‘culprit’ of present day greenhouse scourge, might have played a vital role in helping ancient Earth escape from complete glaciation, scientists in the UK have revealed.

In their study published recently in the Nature Geoscience magazine, scientists have said that during the Cryogenian period, about 840 to 635 million years ago, the Earth never froze completely.

This revelation contradicts the Snowball Earth hypothesis, which envisages a fully frozen Earth that was locked in ice for many millions of years as a result of a run-away chain reaction that caused the planet to cool.

“Something must have kept the planet's equatorial oceans from freezing over,” said Professor Phillip Allen of Imperial College London's Department of Earth Science and Engineering, the lead author of the research paper.

“In the climate change game, carbon dioxide can be both saint and sinner. These days we are so concerned about global warming and the harm that carbon dioxide is doing to our planet. However, approximately 600 million years ago, this greenhouse gas probably saved ancient Earth and its basic life forms from an icy extinction,” he said.

Allen, who has previously published research papers, has found evidence demonstrating hot and cold cycles in the Cryogenian period. He said that a plethora of papers has been published and much debate has been devoted to the Snowball Earth theory since it was originally proposed.

"Sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans. This evidence contradicts the Snowball Earth theory, which suggests the oceans were frozen over. Yet, many scientists still believe Snowball Earth to be correct," the scientist said.

What enabled the Earth to escape from a complete freeze is not certain, but the UK scientists in their review, point to a recent research carried out at the University of Toronto. This speculates that the advancing ice was stalled by the interaction of the physical climate system and the carbon cycle of the ocean, with carbon dioxide playing a key role in insulating the planet.

Scientists at Toronto are of the view that as Earth's temperatures cooled, oxygen was drawn into the ocean, where it oxidised organic matter, releasing the greenhouse gas carbon dioxide into the atmosphere.

Allen is hopeful that his recent study will prompt climate modellers to realign their thinking about the Cryogenian period and review their models to reflect a warmer Earth during this time.

"There is so much about Earth's ancient past that we don't know enough about. So it is really important that climate modellers get their targets right. They need to build into their calculations a warmer planet, with open oceans, despite lower levels of solar radiation at this time. Otherwise, climate models about the Earth's distant past are aiming for a target that never existed," Allen said.