Did life on Earth be­gin 3.5 bil­lion years ago?

The Week (US) - - News 21 -

Sci­en­tists say they have found proof that life on Earth emerged un­der harsh con­di­tions more than 3.5 bil­lion years ago—a dis­cov­ery that, if con­firmed, sig­nif­i­cantly in­creases the chances that life is com­mon­place in the uni­verse. UCLA sci­en­tist J. Wil­liam Schopf first claimed back in 1993 that an­cient rocks in West­ern Aus­tralia con­tained “mi­cro­fos­sils” of prim­i­tive life. But other sci­en­tists dis­puted that find­ing, ar­gu­ing that the tiny cylin­dri­cal and fil­a­men­tous shapes he had iden­ti­fied were merely min­er­als. Now Schopf, work­ing with a team at UCLA and the Uni­ver­sity of Wis­con­sin–Madi­son, says he has proof that the mi­cro­fos­sils are the real deal—mak­ing them the old­est fos­sils ever found on Earth, re­ports Smith­so­ni­anMag .com. In a painstak­ing 10-year process, the re­searchers found that the ra­tio of car­bon iso­topes in each sus­pected fos­sil were dif­fer­ent from those of the sur­round­ing rock—a clear sign the fos­sils truly were bi­o­log­i­cal life. Schopf and his col­leagues point out that this “prim­i­tive and di­verse group of or­gan­isms” ex­isted be­fore Earth gained an oxy­gen-rich at­mos­phere, sug­gest­ing that some of them re­lied on the sun for en­ergy while oth­ers thrived on meth­ane. “By 3.465 bil­lion years ago, life was al­ready di­verse on Earth—prim­i­tive pho­to­syn­the­siz­ers, meth­ane pro­duc­ers, meth­ane users,” says Schopf. “This tells us life had to have be­gun sub­stan­tially ear­lier.” If prim­i­tive life forms could de­velop un­der the harsh, oxy­gen-free con­di­tions of early Earth, Schopf con­cludes, “life in the uni­verse should be wide­spread.”

A thin slice of the mi­cro­fos­sils

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