Oldest piece of earth crust reveals how life began
Posted on Feb 24 2014 | IANS
New York, Feb 24 : The truth about how the earth prepared itself for life is out. The earth's crust first formed at least 4.4 billion years ago - just 160 million years after the formation of our solar system - and then cooled to become habitable, reveals research.
The answer lies in a 4.4 billion-year-old zircon - the oldest known terrestrial material of any kind - that was extracted from a remote rock in western Australia.
"This confirms our view of how the earth cooled and became habitable. This may also help us understand how other habitable planets would form," said John Valley, a geochemist with University of Wisconsin-Madison in the US.
The study strengthens the theory of a 'cool early earth' where temperatures were low enough for liquid water, oceans and a hydrosphere not long after the planet's crust congealed from a sea of molten rock.
"The study reinforces our conclusion that earth had a hydrosphere before 4.3 billion years ago and possibly life not long after," explained Valley.
Life on earth began at least 3.5 billion years ago because that is the age of the oldest rocks with fossil evidence of life on earth.
The earth was assembled from a lot of heterogeneous material from the solar system.
The early earth experienced intense bombardment by meteors, including a collision with a Mars-sized object about 4.5 billion years ago.
That formed our moon, and melted and homogenised the earth.
To understand the phenomenon, the researchers used a new technique called atom-probe tomography that, in conjunction with secondary ion mass spectrometry, permitted the scientists to accurately establish the age and thermal history of the zircon.
Instead of being randomly distributed in the sample, as predicted, lead atoms in the zircon were clumped together, like 'raisins in a pudding', noted Valley.
The zircon formed 4.4 billion years ago, and at 3.4 billion years, all the lead that existed at that time was concentrated in these hotspots. This means a new page of the thermal history recorded by these tiny zircon time capsules, said the study published in the journal Nature Geoscience.