Clarification on Earth's age

Hello world;

At this site

http://www.talkorigins.org/faqs/faq-age-of-earth.html

I read:

"... figure of 4.55 billion years for the Earth's actual age.

The most direct means for calculating the Earth's age is a
Pb/Pb isochron age, derived from samples of the Earth and
meteorites. This involves measurement of three isotopes of lead
(Pb-206, Pb-207, and either Pb-208 or Pb-204). A plot is
constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.

If the solar system formed from a common pool of matter,
which was uniformly distributed in terms of Pb isotope
ratios, then the initial plots for all objects from that pool
of matter would fall on a single point. ..."


My question concerns those Pb isotope ratios. According to my
fuzzy thinking the only time when they would have been
uniformly distributed would be shortly after the explosions of
the super-novas which produced the clouds from which our solar
system subsequently formed.

If this is correct, then the 4.55 billion year estimate is not
an estimate of Earth's age, but of the average time of the
explosions of the super-novas which contributed heavy elements
to our solar system.

Could someone tell me if I am to basically right or wrong
about this.

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------

"Friar Broccoli" wrote in message
oups.com...
Hello world;

At this site

http://www.talkorigins.org/faqs/faq-age-of-earth.html

I read:

"... figure of 4.55 billion years for the Earth's actual age.

The most direct means for calculating the Earth's age is a
Pb/Pb isochron age, derived from samples of the Earth and
meteorites. This involves measurement of three isotopes of lead
(Pb-206, Pb-207, and either Pb-208 or Pb-204). A plot is
constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.

If the solar system formed from a common pool of matter,
which was uniformly distributed in terms of Pb isotope
ratios, then the initial plots for all objects from that pool
of matter would fall on a single point. ..."


My question concerns those Pb isotope ratios. According to my
fuzzy thinking the only time when they would have been
uniformly distributed would be shortly after the explosions of
the super-novas which produced the clouds from which our solar
system subsequently formed.

If this is correct, then the 4.55 billion year estimate is not
an estimate of Earth's age, but of the average time of the
explosions of the super-novas which contributed heavy elements
to our solar system.

Could someone tell me if I am to basically right or wrong
about this.

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------

When the earth was formed (some say during a collision with a mars-sized
body), it was mostly molten, so the lead clock would have reset at that
time.

George

" George" wrote in message
...


When the earth was formed (some say during a collision with a mars-sized
body), it was mostly molten, so the lead clock would have reset at that
time.

It is the Moon that is thought to have come into being
due to a collision between the young Earth and a Mars
sized body.

"Greg Neill" wrote in message
.. .
" George" wrote in message
...


When the earth was formed (some say during a collision with a mars-sized
body), it was mostly molten, so the lead clock would have reset at that
time.

It is the Moon that is thought to have come into being
due to a collision between the young Earth and a Mars
sized body.

Yes, and the fledgling Earth was completely disrupted, which is why the
Earth and the Moon are the same age.

George

George wrote:
"Friar Broccoli" wrote in message

If this is correct, then the 4.55 billion year estimate is not
an estimate of Earth's age, but of the average time of the
explosions of the super-novas which contributed heavy elements
to our solar system.

" George" wrote in message
...

"Greg Neill" wrote in message
.. .
" George" wrote in message
...


When the earth was formed (some say during a collision with a mars-sized
body), it was mostly molten, so the lead clock would have reset at that
time.

It is the Moon that is thought to have come into being
due to a collision between the young Earth and a Mars
sized body.

Yes, and the fledgling Earth was completely disrupted, which is why the
Earth and the Moon are the same age.

What do you mean by "completely disrupted"? Vaporized?
Returned to a completely unaggregated cloud?

I think it more likely that the impact caused a reheating
and perhaps complete resurfacing of the Earth while the
Moon coagulated from the debris whacked off of the
Earth. So the Earth's isotope "clocks" would have been
reset at that time.

The trick to radioisotopic aging is to isolate a particular radioactive
isotope and the nucleus to which it decays. For example, rubidium-87
decays into stontium-87 with a half-life of 47.0 billion years.
Therefore the ratio of rubidium-87 to strontium-87 can yield the age at
which that rock solidified. Because the rock likely contained strontium
to begin with, geologists can use as a marker another isotope of
strontium that is not the result of radioactive decay. A comparison of
the ratio of the strontium created from radioactive decay to that not so
to the ratio of rubidium-87 to the strontium created by the decay (in
other words a ratio of two ratios) can then be used to calculate when
the rock solidified. [ref. Universe, 5th edition, by Kaufmann and Freedman]

In other words, rocks found on the surface of the Moon can be aged
because they are likely to have been there since the Moon solidified.
Rocks from different areas on the Moon when dated in the above method
can be used to verify the results, because it is not likely one would
find fall rocks on the surface at different locations that all
originated from the same solidification event. So, by comparing the
ages arrived at using rock samples from some 7 different sites, the age
of solidification of the Moon can be derived.

Since it is not likely that the Moon formed independent of the Earth
because of similarities of chemical isotopes present in each body's rock
samples, then determination of the Earth's age follows from that of the
Moon. Some of the oldest rocks found on Earth date from about 3.3 to
3.5 billion years, consistent with the observation that ours is a
geologically active world with a surface that changes over time. As
surface rock is subducted below the surface, it becomes molten and this
resets the clock on this material simply because you know longer have
the ability to keep radioactive element and element into which it decays
together. Once that material reappears above the surface and
solidifies, say by volcanic eruption, then we can again use the ratio of
ratios idea to date that particular solidification event.



Friar Broccoli wrote:

The only way I can imagine for resetting the clock is creating new
lead isotopes. A collision between two planets obviously cannot
do this, so how is the clock reset?

Scott Miller wrote:
The trick to radioisotopic aging is to isolate a particular radioactive
isotope and the nucleus to which it decays. For example, rubidium-87
decays into stontium-87 with a half-life of 47.0 billion years.
Therefore the ratio of rubidium-87 to strontium-87 can yield the age at
which that rock solidified. Because the rock likely contained strontium
to begin with, geologists can use as a marker another isotope of
strontium that is not the result of radioactive decay. A comparison of
the ratio of the strontium created from radioactive decay to that not so
to the ratio of rubidium-87 to the strontium created by the decay (in
other words a ratio of two ratios) can then be used to calculate when
the rock solidified.

Thanks for putting in the time to explain this to me.
I believe I understand now, and after a few days of
mulling it over, I'm sure I will understand better.

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------

"Greg Neill" wrote in message
.. .
" George" wrote in message
...

"Greg Neill" wrote in message
.. .
" George" wrote in message
...


When the earth was formed (some say during a collision with a
mars-sized
body), it was mostly molten, so the lead clock would have reset at
that
time.

It is the Moon that is thought to have come into being
due to a collision between the young Earth and a Mars
sized body.

Yes, and the fledgling Earth was completely disrupted, which is why the
Earth and the Moon are the same age.

What do you mean by "completely disrupted"? Vaporized?
Returned to a completely unaggregated cloud?

I think it more likely that the impact caused a reheating
and perhaps complete resurfacing of the Earth while the
Moon coagulated from the debris whacked off of the
Earth. So the Earth's isotope "clocks" would have been
reset at that time.


According to the theory, the cores of the fledgling earth and the impacter
merged. Such an event, if it did indeed occur, would certainly completely
disrupt the early earth. I see no way that the cores could have merged and
not completely disrupt the earth. At any rate, the impact would have reset
the isotope clocks.

George

"Friar Broccoli" wrote in message
oups.com...
George wrote:
"Friar Broccoli" wrote in message

If this is correct, then the 4.55 billion year estimate is not
an estimate of Earth's age, but of the average time of the
explosions of the super-novas which contributed heavy elements
to our solar system.

.

When the earth was formed (some say during a collision with a mars-sized
body), it was mostly molten, so the lead clock would have reset at that
time.

The only way I can imagine for resetting the clock is creating new
lead isotopes. A collision between two planets obviously cannot
do this, so how is the clock reset?

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------

Isotopic clocks have been shown many times to have been reset under certain
circumstances. The isotopic clocks in granite can be reset through
metamorphism (and more than once, if it undergoes repeated metamorphism),
for instance. It is not a new phenomenon.

George