London, March 11 (ANI): A new analysis has suggested that microbes living deep underground could have survived the massive barrage of impacts that blasted the Earth 3.9 billion years ago.
This means that today's life might be descended from microbes that arose as far back as 4.4 billion years ago, when the oceans formed.
Around 3.9 billion years ago, shifts in the orbits of the gas giant planets are thought to have disrupted other objects in the solar system, sending many hurtling into the inner planets.
Geologists call that time the Hadean Eon, and thought its fiery hell of impacts would have sterilised the Earth.
But, according to a report in New Scientist, a new study by Oleg Abramov and Steve Mojzsis of the University of Colorado in Boulder suggests hardy life-forms could have survived if they were buried underground.
Using a computer model, they sent 200 million billion tonnes of mass - in rocks with the same mass distribution as those in today's asteroid belt - slamming into the planet.
The biggest impacts would have done the most damage - a 500-kilometre-wide blockbuster would have spread a 350-metre-deep layer of 1200 degrees Celsius ejecta over the planet.
Yet, heat from the impacts would not have penetrated very deeply into the underlying solid crust.
The layer heated to the sterilization point, about 110 degrees C, would be only about 300 meters thick.
High-temperature 'extremophile' microbes, like those in the hot springs of Yellowstone National Park, US, would have survived at greater depths, down to their limit of about 4 km.
Moreover, the impacts might have helped provide a refuge for these heat-loving microbes by creating cracks in the rocky crust that water could flow into.
As to how far back could life have originated, the oldest isotopic evidence of life comes from rocks that formed 3.83 billion years ago, soon after the "late heavy bombardment" that battered the planet in the Hadean period.
But, heat-loving microbes appear to be among the Earth's earliest life-forms, and may have developed as early as 4.4 billion years ago.
That's when the hot young Earth, whose top few hundred kilometers had probably been vaporized 100 million years before, in the impact that formed the Moon, would have cooled enough for seas to form.
According to Mojzsis, "For all intents and purposes, life could have started 4.4 billion years ago, and the late heavy bombardment pruned, rather than frustrated, life." (ANI)