Life on Earth was 'hell' 3.5 billion years ago

Canberra, Nov 28 : A scientist has developed a computer model which suggests that life on Earth was 'hell' 3.5 billion years ago, with a layer of rock deep inside the mantle resulting in the planet being covered by a sea of lava several kilometers thick.

According to a report by ABC News, using computer models of the earth's interior, Dr Geoff Davies of the Australian National University in Canberra, believes these events would have left only the hardiest of life to survive and may explain how the continents formed.

Heat formed under the surface of the earth's crust due to natural radioactive decay. This heat drives convention currents in the mantle, which push against the tectonic plates that form the crust.

Occasionally, one plate slides under another, a process known as subduction.

Davies developed a computer model of the earth's interior to examine how this subduction process interacts with the mantle.

His model shows that during the earth's first billion years, rock from the crust dives down to a region between the inner and outer mantle, approximately 660 to 750 kilometres below the earth's surface, where it accumulates to form a 'basaltic barrier'.

"Once that blocking layer is there, there's no way for the heat from the deep mantle to escape to the surface," Davies said.

The heat continues to increase in temperature and eventually breaks through the barrier making its way to the surface.

"It melts as it reaches the lower pressure near the top of the mantle and the melted rock erupts as lava flows," said Davies. "The lava flows could pile up to a thickness of ten to fifteen kilometers over much of the earth," he added.

According to Davies' model, these volcanic events last for a million years and occur about once every 100 million years.

Davies added that these events would release large amounts of carbon dioxide and sulfur dioxide, affecting the chemistry of the oceans and atmosphere, and leaving only the hardiest bacteria alive.

This process continues until the earth is approximately 1 billion years old.

"The radioactive heating in the mantle slowly decreases and the mantle cools and moves more slowly, so the tectonic plates become thicker," said Davies.

After this point in time, tectonic plates that undergo subduction are heavier and pass into the inner mantle where they are broken apart, preventing them from forming a basaltic barrier.

Davies believes his finding may help provide a better understanding of how the continents formed.

ANI