Fos­sils old­est sign of life on planet, sci­en­tists say

Baltimore Sun - - NATION & WORLD - By Joel Achenbach

Sci­en­tists prob­ing a newly ex­posed, formerly snow-cov­ered out­crop­ping in Green­land claim they have dis­cov­ered the old­est fos­sils ever seen, the rem­nants of mi­cro­bial mats that lived 3.7 bil­lion years ago.

It’s a stun­ning an­nounce­ment in a sci­en­tific field that is al­ways con­tentious. But if con­firmed, this would push the es­tab­lished fos­sil record more than 200 mil­lion years deeper into the Earth’s early his­tory, and pro­vide sup­port for the view that life ap­peared soon after the Earth formed and may be com­mon­place through­out the uni­verse.

A team of Aus­tralian ge­ol­o­gists an­nounced its dis­cov­ery in a pa­per ti­tled “Rapid emer­gence of life shown by dis­cov­ery of 3,700-mil­lion-year-old mi­cro­bial struc­tures,” pub­lished Wed­nes­day in Na­ture.

They made their find in July 2012 while do­ing field re­search in Isua, a re­gion of Green­land so re­mote that they had to travel there by he­li­copter. The site is known for hav­ing the old­est rocks on Earth, in what is known as the Isua supracrustal belt.

Allen Nut­man, a Univer­sity of Wol­lon­gong ge­ol­o­gist who has stud­ied the rocks there since 1980, said one day he and his col­leagues were work­ing at the site when they spied some out­crop­pings they’d never seen be­fore. The for­ma­tions had been ex­posed where the snow pack had melted — the re­sult, Nut­man said, of the global warm­ing that is so pro­nounced in Green­land or of low lev­els of snow­fall the pre­vi­ous win­ter.

They ex­am­ined the out­crop­ping and saw some­thing in­trigu­ing: con­i­cal struc­tures less than two inches high. They look like fos­silized mi­cro­bial mats — ba­si­cally, pillows of slime — known as stro­ma­to­lites, which are formed to­day by bac­te­rial com­mu­ni­ties liv­ing in shal­low wa­ter.

“We all said, ‘ This is amaz­ing. These look like stro­ma­to­lites,’ ” Nut­man said.

Sub­se­quent lab­o­ra­tory anal­y­sis es­tab­lished that the for­ma­tion is 3.7 bil­lion years old, and turned up ad­di­tional chem­i­cal sig­na­tures con­sis­tent with a bi­o­log­i­cal ori­gin for the con­i­cal struc­tures, Nut­man said.

Fos­silized stro­ma­to­lites nearly 3.5 bil­lion years old have pre­vi­ously been found in Western Aus­tralia.

The Aus­tralian re­searchers do not con­tend that these stro­ma­to­lites rep­re­sent the first ex­am­ples of life on the planet. Rather, these would have to be the de­scen­dants of the ear­lier life forms.

Earth, along with the other plan­ets in our so­lar sys­tem, formed about 4.5 bil­lion years ago from a cloud of dust and gas swirling around the em­bry­onic sun. For hun­dreds of mil­lions of years, Earth was a harsh, molten world, heav­ily bom­barded by de­bris. At one point, a Mars-sized ob­ject slammed into the Earth and blasted into space the ma­te­rial that even­tu­ally co­hered into the moon.

No one knows how life be­gan on Earth.

Charles Dar­win hy­poth­e­sized that life emerged in a “warm lit­tle pond,” but other re­searchers imag­ine that it emerged around a deep- sea hy­dro­ther­mal vent, or even came to Earth from space.

LAURE GAUTHIEZ/ THE AUS­TRALIAN NA­TIONAL UNIVER­SITY 2012

A field team ex­am­ines rocks in Green­land, known for hav­ing the old­est rocks on Earth.

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