How old is the earth NASA

How old is the earth 4.472 billion years

New dating method aims to clarify the controversial question: It is based on the geological clock.

How old the earth is was once believed to be able to determine exactly to the day: On November 10, 4004 BC, a Monday, Adam and Eve were expelled from paradise, according to James Usher, Archbishop of Ireland , Told in 1650 in his "Annals of the Old Testament, derived from the earliest beginners in the world", in which he added up the genealogies of the Old Testament for the time before the birth of Christ. Some still believe that today, the “young earth creationists”, otherwise the method of calculation of science has prevailed.

And even for that there was once an exact value: the physicist William Thompson (later: Lord Kelvin) calculated 30 million in 1862 from the heat radiation of the earth, he made Charles Darwin, who himself had estimated ten times this from geology, “a For a long time "his" most acidic problems ": 30 million would have been far too short for evolution. But Thompson had made a mistake or assumed the false premise that the earth was a solid body; heat escapes differently from one of these than from one that is internally liquid.

And how old is she really? You only know that by thumb. The first objects in the solar system existed 4.567 billion years ago, as their remnants, meteorites, show. But their dates cannot be precisely transferred to the earth; it was there sometime during the first 150 million years of the solar system. And their formation, like that of the other planets, is imagined as follows: At first there was only dust, it came together to form small planetesimals, they got bigger and fewer because and when they crumbled into one another.


Birth of the moon, birth of the earth

And at some point the earth was there. But that is also a question of definition: It was only correct when the initially glowing magma ball was covered with a solid crust. It probably happened several times, then a large celestial body struck and melted everything again. Last came Theia, an impact the size of a Mars, from this collision the moon came into being. And when the earth was encrusted again, it was finally there. But on the outside it was no longer the same as before: when everything melts, some elements migrate into the core; they are siderophiles who like to team up with iron, such as platinum and iridium.

They are correspondingly rare in the earth's crust. But they are already there: in its history, the earth has always been bombed and supplied with material, and it is today too: asteroids, meteorites, cosmic dust. They also bring siderophilic elements, and with them a clock that documents the age of the earth: We know that after the impact of Theia there were no more siderophilic elements in the earth's crust; you can estimate how many of them are there today, and you can estimate how much material has flown in from space and has accumulated.

From all this a group around Seth Jacobson (Bavarian Geoinstitut) has now calculated the age of the earth: It was 95 million years after the first witnesses of the solar system, plus / minus 32 million (Nature, 508, p.84). This corresponds in the order of magnitude with age determinations from radioactive decay, but they are not exactly exact, and the current calculation is only a calculation that also uses a lot of unknowns or hypotheses. They begin with the formation of the planets, they continue with the estimation of the material arriving from space.

And they culminate in the impact of “Theia”, about which considerable doubts have recently surfaced. But Jacobson is delighted: "We were thrilled to find a timepiece for the formation that is not based on radiometric methods."

("Die Presse", print edition, 04/04/2014)