Age of Earth vs Age of Starstuff Making Earth

Jeff Kiehn wrote in message ...
Hello all-

We always hear the age of the earth is 4.6GY old. I understand this is
calculated based on radioisotope dating. I've wondered for a long time
whether that age takes into account the radioactive decay of elements
BEFORE the earth was formed, i.e. when the elements were formed in a
distant supernova from which the material the earth was made. I don't
believe anyone would know how long ago that distant supernova
happened or where it was, but surely the radioactive elements would have
started decaying then, not when 'the earth formed'. How do you resolve
this question?

Thank you.

Jeff

Gee Wally, Idon't know!?!

On Fri, 27 Feb 2004 19:06:06 -0800, Jeff Kiehn wrote:

Hello all-

We always hear the age of the earth is 4.6GY old. I understand this is
calculated based on radioisotope dating. I've wondered for a long time
whether that age takes into account the radioactive decay of elements
BEFORE the earth was formed, i.e. when the elements were formed in a
distant supernova from which the material the earth was made. I don't
believe anyone would know how long ago that distant supernova
happened or where it was, but surely the radioactive elements would have
started decaying then, not when 'the earth formed'. How do you resolve
this question?

The clock starts when some matter becomes solid, not the moment the element
is formed, because only in solids the daugther elements stay next to the
parent. And this means we cannot measure the age of the Earth, just the ages
some rocks became solid.

Joachim.


--
This post is free post; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

Joachim Verhagen )
WWW http://www.xs4all.nl/~jcdverha/ (Science Jokes)

"Jeff Kiehn" wrote in message
...
Hello all-

We always hear the age of the earth is 4.6GY old. I understand this is
calculated based on radioisotope dating. I've wondered for a long time
whether that age takes into account the radioactive decay of elements
BEFORE the earth was formed, i.e. when the elements were formed in a
distant supernova from which the material the earth was made. I don't
believe anyone would know how long ago that distant supernova
happened or where it was, but surely the radioactive elements would have
started decaying then, not when 'the earth formed'. How do you resolve
this question?

Thank you.

Jeff

The age of the Earth is deduced mainly from the ages of meteorites, which
tend to have a maximum age of 4.55 billion years. This is believed to be
the age of the solar system and recent studies of the solar interior confirm
this to be the age of the Sun to about 1-2%.

The rocks on the Earth, and the meteorites, start their radioactive dating
clock going the moment they solidify, trapping daughter products in the
rocks. The oldest rocks found today on the Earth's surface are about 3.8
billion years old (there may be a better figure available now).

We don't really know whether the heavy elements were created in one
supernova or several, but the latter seems likely. There are other
processes that build heavy elements and recycle them.

It is possible in principle to calculate the expected supernova yield of the
various uranium isotopes, and by extrapolating back 4.5 billion years this
can be compared to the expected proportions of U-235 and U-238 on Earth (for
example). Other methods involve looking for evidence of short-lived
isotopes in meteorite material.

Such comparisons suggest that an element-forming event took place around the
time of the solar system's formation. Whether the supernova actually
triggered the collapse of the presolar nebula is not known.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

Joachim Verhagen wrote:

On Fri, 27 Feb 2004 19:06:06 -0800, Jeff Kiehn wrote:

Hello all-

We always hear the age of the earth is 4.6GY old. I understand this is
calculated based on radioisotope dating. I've wondered for a long time
whether that age takes into account the radioactive decay of elements
BEFORE the earth was formed, i.e. when the elements were formed in a
distant supernova from which the material the earth was made. I don't
believe anyone would know how long ago that distant supernova
happened or where it was, but surely the radioactive elements would have
started decaying then, not when 'the earth formed'. How do you resolve
this question?

The clock starts when some matter becomes solid, not the moment the element
is formed, because only in solids the daugther elements stay next to the
parent. And this means we cannot measure the age of the Earth, just the ages
some rocks became solid.

Joachim.


Thanks for your response. I should have realized that's the reason-
it's so obvious.

Again, thanks, Joachim.

On Sat, 28 Feb 2004 09:58:37 +0100, Joachim Verhagen
wrote:

The clock starts when some matter becomes solid, not the moment the element
is formed, because only in solids the daugther elements stay next to the
parent. And this means we cannot measure the age of the Earth, just the ages
some rocks became solid.

I'm curious, though, as to what would stop some of the daughter
elements being incorporated into rocks? Not argon I suppose, but why
couldn't e.g. lead be incorporated into rocks along with uranium?

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace

Russell, I think Joachim is right. It does make sense. When radioisotopes
decay in interstellar dust and that dust is then incorporated into a large
hot molten body, each daughter componant would separate according to its
density and chemical (periodic table) properties, so lead wouldn't end up
with the original uranium. (In fact, I could be wrong, but I don't think
lead ores- like galena- are found with too much uranium nearby). Only when
the rocks have formed (i.e. the beginning of the earth) would the daughter
isotopes be found with the parent.

Another poster to this question added that we get a better idea of the age
of the solar system mainly from studying meteorites, which presumably
solidified during the formation of the solar system before the bulky earth
did.

Jeff

"Russell Wallace" wrote in message
...
On Sat, 28 Feb 2004 09:58:37 +0100, Joachim Verhagen
wrote:

The clock starts when some matter becomes solid, not the moment the
element
is formed, because only in solids the daugther elements stay next to the
parent. And this means we cannot measure the age of the Earth, just the
ages
some rocks became solid.

I'm curious, though, as to what would stop some of the daughter
elements being incorporated into rocks? Not argon I suppose, but why
couldn't e.g. lead be incorporated into rocks along with uranium?

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace

On Sun, 29 Feb 2004 00:44:11 GMT, (Russell
Wallace) wrote:

On Sat, 28 Feb 2004 09:58:37 +0100, Joachim Verhagen
wrote:

The clock starts when some matter becomes solid, not the moment the element
is formed, because only in solids the daugther elements stay next to the
parent. And this means we cannot measure the age of the Earth, just the ages
some rocks became solid.

I'm curious, though, as to what would stop some of the daughter
elements being incorporated into rocks? Not argon I suppose, but why
couldn't e.g. lead be incorporated into rocks along with uranium?

I guess the gravity of Earth separates elements according to density of the
molecules they are in. But that would not work on asteroids. Maybe someone
in the sci.geo groups knows. I did an undergraduate minor in geophysics
twenty years ago, but either it was not covered or I have forgotten. :-(

Joachim.

--
This post is free post; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

Joachim Verhagen )
WWW http://www.xs4all.nl/~jcdverha/ (Science Jokes)

"Al & Sylvia" wrote in message
news:_Ff0c.6421$h23.1539@fed1read06...
Russell, I think Joachim is right. It does make sense. When
radioisotopes
decay in interstellar dust and that dust is then incorporated into a large
hot molten body, each daughter componant would separate according to its
density and chemical (periodic table) properties, so lead wouldn't end up
with the original uranium. (In fact, I could be wrong, but I don't think
lead ores- like galena- are found with too much uranium nearby). Only
when
the rocks have formed (i.e. the beginning of the earth) would the daughter
isotopes be found with the parent.

Another poster to this question added that we get a better idea of the
age
of the solar system mainly from studying meteorites, which presumably
solidified during the formation of the solar system before the bulky earth
did.

Jeff

"Russell Wallace" wrote in message
...
On Sat, 28 Feb 2004 09:58:37 +0100, Joachim Verhagen
wrote:

The clock starts when some matter becomes solid, not the moment the
element
is formed, because only in solids the daugther elements stay next to
the
parent. And this means we cannot measure the age of the Earth, just
the
ages
some rocks became solid.

I'm curious, though, as to what would stop some of the daughter
elements being incorporated into rocks? Not argon I suppose, but why
couldn't e.g. lead be incorporated into rocks along with uranium?

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace



The initial amount of some daughter isotope doesn't matter, and its presence
would not prevent the determination of the age of the rock. The key is the
use of a measuring technique called the isochron method. In this technique,
various bits of rock give present ratios of parent isotope to daughter
isotope. If you plot them on a graph, and draw a line through the results,
then the slope of the line is related to the age of the rock. If the points
fail to lie on a line but scatter all over the place, then the rock cannot
be dated because something has happened to it to disturb the build-up of
decay products, such as partial heating or melting at some point in its
history.

If you get a good line, then the date can be readily ascertained most of the
time. The more tests that are performed, the more reliable the result.

See

http://www.talkorigins.org/faqs/isochron-dating.html

for further details.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

On Sun, 29 Feb 2004 16:29:25 +0000 (UTC), "Mike Dworetsky"
wrote:

[explanation]

See

http://www.talkorigins.org/faqs/isochron-dating.html

for further details.

Ah, that explains it, thanks!

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace