Most of the water that formed the Earth’s oceans and the elements essential for life, such as carbon and nitrogen, appeared when the formation of the planet was almost complete, so much later than previously theorized.
This is what a new study in Nature suggests, which therefore contrasts with past geological investigations and studies according to which these elements, essential for water, and therefore also for life, were already on the planet at the beginning of formation.
Fischer-Gödde explains the method of study: the researchers have analyzed some of the oldest of the mantle rocks among those that have remained preserved, analyses that allow us to scrutinize the oldest history of the Earth: “We have compared the composition of the oldest, about 3.8 billion years ago, of the mantle rocks of the Aegean Archaean with the composition of the asteroids from which they were formed and with the composition of the Earth’s mantle today”.
The researchers analyzed in particular the abundance of isotopes of a metal belonging to the platinum group called ruthenium in the earth’s mantle of the archaean period. This rare metal can be regarded as an indicator of the late growth phase of the Earth as Mario Fischer-Gödde of the Institute of Geology and Mineralogy at the University of Cologne explains: “Platinum [group] metals such as ruthenium have an extremely high tendency to combine with iron. Therefore, when the Earth was formed, ruthenium must have been completely discharged into the metal core of the Earth”.
The conclusions of this study therefore reinforce a theory that water on Earth arrived through impacts, numerous in the early periods after the formation of the Earth, of asteroids and comets, as explained by Carsten Münker, researcher at the University of Cologne participating in the study: “The fact that we are still finding traces of rare platinum metals in the Earth’s mantle means that we can assume that they were added only after the formation of the core was completed and were certainly the result of subsequent collisions of the Earth with asteroids or smaller planetesimals.
And given that it has been shown by other studies that life on Earth is very ancient and that the first forms of life appeared not long after the formation of the planet, it is worth noting that life on Earth began surprisingly quickly, practically within a few hundred million years after the formation of the first oceans.
These conclusions, among other things, instill much greater hope of finding life on other planets: if life began here on Earth so quickly, then perhaps those random reactions that originated it may not be as rare as previously thought.