Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: chris on 10/04/2009 11:02:09

Title: How do we date the Earth?
Post by: chris on 10/04/2009 11:02:09
The accepted age of the Earth is about 4500 million years. How do scientists know this?

Chris
Title: How do we date the Earth?
Post by: RD on 10/04/2009 21:09:35
By the abundance of certain radio isotopes on Earth ...

Quote
The ages of Earth and Moon rocks and of meteorites are measured by the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals and that decay with half lives of 700 million to more than 100 billion years to stable isotopes of other elements. These dating techniques, which are firmly grounded in physics and are known collectively as radiometric dating, are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to rehomogenize its radioactive elements.
http://pubs.usgs.gov/gip/geotime/age.html

Title: How do we date the Earth?
Post by: Chemistry4me on 11/04/2009 04:26:48
How do they know where to start finding rocks?
Title: How do we date the Earth?
Post by: RD on 11/04/2009 04:35:46
How do they know where to start finding rocks?

A Geiger counter would be useful to find Uranium ... http://scifun.chem.wisc.edu/CHEMWEEK/PDF/Uranium_Clock.pdf
Title: How do we date the Earth?
Post by: Madidus_Scientia on 11/04/2009 10:17:04
How do we date the Earth?

That's a good question, where do you take a nice planet out for dinner these days?

Maybe you could get her a ring :P
Title: How do we date the Earth?
Post by: Chemistry4me on 11/04/2009 12:18:49
I think it's a he.
Title: How do we date the Earth?
Post by: Karen W. on 11/04/2009 12:50:37
How do we date the Earth?

That's a good question, where do you take a nice planet out for dinner these days?

Maybe you could get her a ring :P

Great minds think alike! Lol...

 Take her for a nice spin....Show her the stars... and buy her a silver platter so she can see every cloud has a silver lining or you could just introduce her to the man in the moon!

  Seriously I honestly don't know....but could examining the core of the earth...shed any light on its age.. or perhaps the solar system?

ialways thought it was from rock and mineral samples so I assumed going deeper towards or into the center or core could answer how old the earth could be!
Title: How do we date the Earth?
Post by: chris on 11/04/2009 13:01:27
Take her out for a coffee at...Starbucks...!
Title: How do we date the Earth?
Post by: Andrew K Fletcher on 11/04/2009 14:36:46
It's a very good question Chris and one that deserves a lot of attention.

Have we dated radioactive isotopes and rocks rather than the age of the earth?
Title: How do we date the Earth?
Post by: Karen W. on 11/04/2009 15:02:51
Take her out for a coffee at...Starbucks...!

ummmmmmmm that would send her into orbit!

What about the samples of the core etc....
Title: How do we date the Earth?
Post by: RD on 11/04/2009 15:30:07
Have we dated radioactive isotopes and rocks rather than the age of the earth?

The isotope ratios tell when the rock solidified, so tell the age the surface of the Earth became solid.

Quote
These dating techniques, which are firmly grounded in physics and are known collectively as radiometric dating, are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to rehomogenize its radioactive elements.
http://pubs.usgs.gov/gip/geotime/age.html


Quote
The oldest minerals dated so far by the U/Pb technique are zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, with an age of 4.404 billion years, interpreted to be the age of crystallization.
http://en.wikipedia.org/wiki/Zircon
Title: How do we date the Earth?
Post by: Chemistry4me on 12/04/2009 04:23:08
Quote
The oldest minerals dated so far by the U/Pb technique are zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, with an age of 4.404 billion years, interpreted to be the age of crystallization.
http://en.wikipedia.org/wiki/Zircon
So it could be possible that the Earth could have even older rocks right?
Title: How do we date the Earth?
Post by: RD on 12/04/2009 06:17:08
So it could be possible that the Earth could have even older rocks right?

Probably all of Earth's first (oldest) crust has been recycled by plate tectonics (http://en.wikipedia.org/wiki/Plate_tectonics).

[Meteorites which have fallen to Earth since Earth's surface solidified would be older than any native Earth rocks].
Title: How do we date the Earth?
Post by: Yomi on 12/04/2009 14:03:15
BY Carbon dating process just as done for rocks .... Try carbon dating in the oldest rock.... [;D] [;D]
Title: How do we date the Earth?
Post by: _Stefan_ on 12/04/2009 14:41:30
Carbon dating is not used for materials over a certain age. The isotope ratios of other elements are used instead.
Title: How do we date the Earth?
Post by: Andrew K Fletcher on 12/04/2009 15:20:01
Another question was asked on the forum: How long would it take with plate tectonics and erosion to completely eradicate all evidence of human existence.

A reply in the region of 3 million years. This timescale is a minute proportion of the highest estimation of the Earth’s age.

Along with humans, went rocks, concrete, iron, steel, stainless steel, glass, all vanished in an estimated 3 million years. (metaphorically speaking)

What, if any chance do we have of truly guestimating the age of the earth with any degree of accuracy ?

At best we have a minimum age for the Earth!

Andrew
Title: How do we date the Earth?
Post by: _Stefan_ on 12/04/2009 16:22:17
Would you care to cite evidence for what you have asserted? The geological record practically falsifies that claim.

The ability of radiometric dating to provide the approximate ages of materials is beyond reasonable doubt.
Title: How do we date the Earth?
Post by: Madidus_Scientia on 12/04/2009 16:42:06
lol @ Starbucks
Title: How do we date the Earth?
Post by: JimBob on 12/04/2009 18:16:13
Another question was asked on the forum: How long would it take with plate tectonics and erosion to completely eradicate all evidence of human existence.

A reply in the region of 3 million years. This timescale is a minute proportion of the highest estimation of the Earth’s age.

Along with humans, went rocks, concrete, iron, steel, stainless steel, glass, all vanished in an estimated 3 million years. (metaphorically speaking)

What, if any chance do we have of truly guestimating the age of the earth with any degree of accuracy ?

At best we have a minimum age for the Earth!

Andrew

Yes, we have a minimum age - about 4.5 billion years BUT this a very accurate age - (zircon crystals) and the other derivations of the Sun solar System as derived from energy expenditure budgets and the backward extrapolation of when the Sun could have originally been formed are very close to the zircon crystal date. The crystals leave no room for any "guestimating."

Title: How do we date the Earth?
Post by: Madidus_Scientia on 13/04/2009 18:22:26
BY Carbon dating process just as done for rocks .... Try carbon dating in the oldest rock.... [;D] [;D]

Carbon dating is used on things that were once living, it won't work on rocks.
Title: How do we date the Earth?
Post by: RD on 13/04/2009 21:39:18
Carbon dating is used on things that were once living, it won't work on rocks.

Minerals do contain organic ("once living") carbon, e.g. coal, limestone. The reason carbon dating cannot be used on them is the half life of Carbon14 (@ 5700 years) is too short compared with the age of the rock (e.g. coal @ 300 million years): there is no longer a measurable level of Carbon 14 in them.
Title: How do we date the Earth?
Post by: Andrew K Fletcher on 14/05/2009 19:37:22
So how do we jump from a minimum age to a maximum age based only on the samples examined?