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Our oceans, extraterrestrial material?

Nov. 17, 2009
Courtesy CNRS - French National 
Center for Scientific Research
and World Science staff

Con­tra­ry to con­ven­tion­al views, the at­mos­phere and the oceans were per­haps not formed from va­pors emit­ted dur­ing in­tense vol­can­ism at the dawn­ing of our plan­et, a sci­ent­ist says.

In­stead, he pro­poses that the wa­ter comes from ice-co­vered as­ter­oids that reached the Earth around a hun­dred mil­lion years af­ter the birth of the plan­ets.

The at­mos­phere and the oceans were per­haps not formed from va­pors emit­ted dur­ing vol­can­ism, but came from space, a sci­ent­ist says. (Im­age cour­tesy Ca­li­forn­ia En­vi­ron­ment­al Re­sources Evalu­a­tion Sys­tem)


Fran­cis Al­barède of the Lab­o­ra­toire des Sci­ences de la Terre at Claude Ber­nard Un­ivers­ity in Ly­on, France, ar­gues that this ef­fect could have re­sulted from tur­bu­lence in the out­er So­lar Sys­tem caused by gi­ant plan­ets. 

His re­search ap­pears in the Oct. 29 is­sue of the re­search jour­nal Na­ture.

Around 4.5 bil­lion years ago, the Earth had enough wa­ter for oceans to form and for life to find niches in the seas and on the con­ti­nents thanks to plate tec­ton­ics, the move­ment of the con­ti­nents. In com­par­i­son, the Moon and Mer­cu­ry are dry, mor­tally cold deserts, Mars dried up very quickly and the sur­face of Ve­nus is an in­fer­no.

Ac­cord­ing to books, the ocean and the at­mos­phere were formed from vol­can­ic gas­es and the Earth’s in­te­ri­or is the source of el­e­ments that go in­to the wa­ter. How­ev­er, the rocks of the Earth’s man­tle, be­neath the crust, have very lit­tle wa­ter, Al­barède notes. The same is true on Earth’s “sis­ter plan­ets,” Ve­nus and Mars. 

The main rea­son pro­posed by Al­barède is that, dur­ing the So­lar Sys­tem’s forma­t­ion, the tem­per­a­ture nev­er dropped enough be­tween the Sun and the or­bit of Ju­pi­ter for wa­ter to be able to con­dense with plan­etary ma­te­ri­al. The ar­ri­val of wa­ter on Earth there­fore hap­pened lat­er, he said.

It is widely ac­cept­ed that ter­res­tri­al plan­ets are formed over sev­er­al mil­lion years by the ag­glomera­t­ion of smaller chunks of ma­te­ri­al, in­creas­ing in size over time. The ar­ri­val of the last of these large ob­jects cor­re­sponds to a huge lu­nar im­pact, 30 mil­lion years af­ter the forma­t­ion of the So­lar Sys­tem, Al­barède ar­gues. In­i­tial­ly, this hurly-burly took place be­tween plan­etary ob­jects lo­cat­ed be­tween the Sun and the as­ter­oid belt. This space, swept by the elec­tro­mag­netic winds of the young Sun, was then too hot for wa­ter and vol­a­tile el­e­ments to con­dense with­in it.

The ma­jor delivery of vol­a­tile el­e­ments on our plan­et could have cor­re­sponded to a phe­nom­e­non that oc­curred some tens of mil­lions of years af­ter the lu­nar im­pact: the big “clean up” of the out­er So­lar Sys­tem in­i­ti­at­ed by the gi­ant plan­ets, Al­barède claims. Due to their very strong gra­vity, they would have sent the fi­nal ice-rich plan­etary rub­ble in all di­rec­tions, in­clud­ing in our own. Pen­e­trat­ing in­to the man­tle through the sur­face, the wa­ter could then have soft­ened the Earth and made it less brit­tle. Plate tec­ton­ics would then have be­gun and with it the emer­gence of con­ti­nents, con­di­tions probably nec­es­sary for life.


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Contrary to conventional views, the atmosphere and the oceans were perhaps not formed from vapors emitted during intense volcanism at the dawning of our planet, a scientist said. Instead, he proposes that the water comes from ice-covered asteroids that reached the Earth around a hundred million years after the birth of the planets Francis Albarède of the Laboratoire des Sciences de la Terre at Claude Bernard University in Lyon, France, argues that this effect could have resulted from turbulence in the outer Solar System caused by giant planets. His research appears in the Oct. 29 issue of the research journal Nature. Around 4.5 billion years ago, the Earth had with enough water for oceans to form and for life to find niches in the seas and on the continents resulting from plate tectonics, the movement of the continents. In comparison, the Moon and Mercury are dry, mortally cold deserts, Mars dried up very quickly and the surface of Venus is a burning inferno. According to books, the ocean and the atmosphere were formed from volcanic gases and the Earth’s interior is the source of elements that go into the water. However, the rocks of the Earth’s mantle, beneath the crust, have very little water, Albarède notes. The same is true on Earth’s “sister planets,” Venus and Mars. The main reason proposed by Albarède is that, during the Solar System’s formation, the temperature never dropped enough between the Sun and the orbit of Jupiter for water to be able to condense with planetary material. The arrival of water on Earth therefore happened later, he said. It is widely accepted that terrestrial planets are formed over several million years by the agglomeration of smaller chunks of material, increasing in size over time. The arrival of the last of these large objects corresponds to the lunar impact, 30 million years after the formation of the Solar System, Albarède argues. Initially, this hurly-burly took place between planetary objects located within the snow line, in other words between the Sun and the asteroid belt. This space, swept by the electromagnetic winds of the young Sun, was then too hot for water and volatile elements to condense within it. The major delivery of volatile elements on our planet could have corresponded to a phenomenon that occurred some tens of millions of years after the lunar impact: the big “clean up” of the outer Solar System initiated by the giant planets, Albarède claims. Due to their very strong gravity, they would have sent the final ice-rich planetary rubble in all directions, including in our own. Penetrating into the mantle through the surface, the water could then have softened the Earth and made it less brittle. Plate tectonics would then have begun and with it the emergence of continents, conditions probably necessary for the appearance of life.