Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: ProjectSailor on 01/10/2015 16:05:31

Title: How old is the earth and how did it develop?
Post by: ProjectSailor on 01/10/2015 16:05:31

I read the data for it.. and potentially disagree with the findings..

The earth has been dated using radiometric dating, surely this would just refer back to when the material was formed which we are told from an exploding supernova not when the planet was formed by the aggregation of these materials.. So would the 4.5 billion years refer to the supernova that gave the solar system its material occurred? as i see no way (unless the earth formed with an element of nuclear fusion to create heavier elements) to actually measure the separation and aggregation of the materials into the ball we know of as earth. 

Title: Re: How old is the earth and how did it develop?
Post by: chiralSPO on 01/10/2015 16:18:51

No, the date refers to the age of the aggregated earth, not just the age of the matter (which, for the record, is the same as the age of the universe, the matter has just been rearranged into a planet)

I believe the age of the earth was determined by looking at the decay of ²³⁸U into lead (I forget which isotope), which has a half life of a few billion years.

Uranium in space will decay just like it does on the Earth, but the produced lead will not necessarily stay near the remaining uranium. Imagine there is a cloud of proto-earth dust. The uranium in the cloud will decay to produce lead, but as the Earth forms the lead and uranium will be separated. Once the crust of the Earth cools and solidifies, though the atoms cannot move as easily. A rock can form that contains uranium but not lead, and then as the decay occurs the lead cannot leave. This is why we can look at the ratio of uranium to lead in certain rocks, and know that that gives the age of the rock.

This doesn't directly give the age of the earth, but the distribution of the age of rocks is highly suggestive that the Earth solidified about 4.5 billion years ago.

Title: Re: How old is the earth and how did it develop?
Post by: ProjectSailor on 01/10/2015 16:40:21

Ah of course I forgot about the liquid phase! where the difference in densities would separate the elements!

But the elements would not be as old as the universe as they are only created in the heart of the star through nuclear fusion.

Thanks for your speedy answer.. it was bugging me when I was talking about mars with a colleague.. (how it came up then I dont know!)

Title: Re: How old is the earth and how did it develop?
Post by: chiralSPO on 01/10/2015 16:47:02

No the elements are not the same age as the universe, but the matter is. It's just reconstituted into heavier elements in stars.