Age of the Earth

"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote in message ...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?
George

Joseph Lazio wrote in message ...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?
George

(George Prehmus) writes:

Joseph Lazio wrote in message ...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?

Given the uncertainties involved in the both the radiochemistry and the
chain of inferences as to when the "giant impact" took place, the few
percent difference between 4.2 Gyr and 4.3 Gyr represents a remarkably
good agreement, IMO !!!


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

(George Prehmus) writes:

Joseph Lazio wrote in message ...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

I don't think that's quite right. The age of the solar system is
dated by meteorites, e.g.,
URL:http://pubs.usgs.gov/gip/geotime/age.html. The ages of
meteorites are all around 4.5 billion years old. Presuming that the
Earth and meteorites did not form at radically different times, this
must then be the age of the Earth.

Last summer I was at a conference in which a couple of researchers
claimed to have dated zircons (mineral inclusions in rocks) to ages
around 4.2 billion years old. I think they were claiming that this
would make them the oldest known objects from Earth.

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?

Given the uncertainties involved in the both the radiochemistry and the
chain of inferences as to when the "giant impact" took place, the few
percent difference between 4.2 Gyr and 4.3 Gyr represents a remarkably
good agreement, IMO !!!


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

"George Prehmus" wrote in message
...
Joseph Lazio wrote in message
...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

snipped explanation

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?
George

Hi George,
I'm not a geologist, but AIUI the oldest rocks found on earth are only about
3.8GY old. All other rocks have been recycled since then. The 'clocks' may
well have been reset at that time, but that was 500MY before the oldest
rocks we can use for dating today.

A very quick google on "oldest earth rocks" came up with
http://www.madsci.org/posts/archives...7637.Es.r.html

As far as I know, the date of 4.5GY or 4.6GY for the solar system comes from
meteor samples.

"George Prehmus" wrote in message
...
Joseph Lazio wrote in message
...
"GP" == George Prehmus writes:

GP I understand that geologial dating is done by comparing long
GP halflife radioactive elements in rocks. The data so gotten shows
GP the time since the rock last was molten. The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA. When that happened, I understand
GP that the entire surface of the Earth was heated to the melting
GP point, resetting the Earth's atomic clock.

snipped explanation

Thanks. That was a help, but OK, so where did I go wrong? Was the heat
of that giant impact not enough to reset the clocks?
George

Hi George,
I'm not a geologist, but AIUI the oldest rocks found on earth are only about
3.8GY old. All other rocks have been recycled since then. The 'clocks' may
well have been reset at that time, but that was 500MY before the oldest
rocks we can use for dating today.

A very quick google on "oldest earth rocks" came up with
http://www.madsci.org/posts/archives...7637.Es.r.html

As far as I know, the date of 4.5GY or 4.6GY for the solar system comes from
meteor samples.

James Whitby wrote in message ...
The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA.

Where does this 4.3 Ga number for the formation of the moon come from?
Some of the returned rock samples may be at least that old, and these
ages may reflect shock processing rather than crust formation (which
itself obviously post-dates 'moon formation'). I don't think the moon
forming event is all that well constrained, but it could have been
substantially earlier, maybe only several tens of millions of years
after the first solids formed in the solar system. For a summary of the
implications of recent tungsten-hafnium dating see
www.lpi.usra.edu/meetings/LPSC98/pdf/1759.pdf
and references therein (interpretation of the radiochemistry is somewhat
model dependent - you have to be very careful about what you mean by
'formation age').

Thank you, gentlemen. The recent article in SCIENCE explains it all very well.
George

James Whitby wrote in message ...
The formation of the
GP Earth is supposedly determined by this method as 4.6 BYA. Yet I
GP undestand that the giant impact which caused to formation of the
GP Moon occurred at about 4.3 BYA.

Where does this 4.3 Ga number for the formation of the moon come from?
Some of the returned rock samples may be at least that old, and these
ages may reflect shock processing rather than crust formation (which
itself obviously post-dates 'moon formation'). I don't think the moon
forming event is all that well constrained, but it could have been
substantially earlier, maybe only several tens of millions of years
after the first solids formed in the solar system. For a summary of the
implications of recent tungsten-hafnium dating see
www.lpi.usra.edu/meetings/LPSC98/pdf/1759.pdf
and references therein (interpretation of the radiochemistry is somewhat
model dependent - you have to be very careful about what you mean by
'formation age').

Thank you, gentlemen. The recent article in SCIENCE explains it all very well.
George