Talk:Oldest rock

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[edit] Australian Zircon

I have a source that says the Australian Zircon fragments have radiometric ages of around 4150Ma rather than 4404Ma. Can anyone find some sources suggesting otherwise? Jason McConnell-Leech 01:47, 3 September 2007 (UTC)

Zircon from the Jack Hills (western Australia) have a wide range in ages, including 4.15 Ga, although the oldest is 4.404 Ga. The source for the 4.404 Ga U-Pb age is reference 1 on the page. Rickert 02:10, 3 September 2007 (UTC)

[edit] ALH84001

Technically, the oldest individual rock found on Earth (so far) is the ALH84001 meteorite, found in Allan Hills, Antarctica in 1984. Its formation has been dated to 4.5 Gyr ago. It is not part of the Earth's geological history (it only landed on Earth about 13,000 years ago), but I have mentioned it in a footnote. Gandalf61 08:26, 27 September 2007 (UTC)

ALH84001 is not the oldest solid object (rock) on earth that has been dated, nor is it's age precisely known. Chondrules from a CR (chondritic) meteorite and calcium-aluminium-rich inclusions from a CV (chondritic) meteorite have well-constrained Pb-Pb isochron ages of 4564.7+-0.6 Ma and 4567.2+-0.2 Ma (Amelin et al., 2002, Science v297(5587) p1678). These ages are older, more precise, and more reliable than the 'preferred' age of 4510+-110 Ma reported for ALH84001 (Nyquist et al., 2001; Space Science Reviews v96(1-4) p105) which appears to be a composite age from different isotopic systems, none as robust as the U-Pb system. Despite the seeming overlapping ages (due to the gargantuan uncertainty on the ALH84001 age) the chondritic meteorites are expected to be among the first condensates from the solar nebula and therefore among the oldest possible solid solar objects, whereas ALH84001 is a cumulate and represents a fragment of a differentiated planetary body, not a 'first-stage' condensate from the solar nebula. Therefore the upper bound on the uncertainty of the age of ALH84001 is unrealistic.

My understanding is that the dates for the CR and CV chondrites are the oldest reliable ages of solid material currently on earth. They are expected to be among the oldest, if not THE oldest solar objects. It is possible that SiC interplanetary dust particles are older (as they may not have an origin in our solar system) but they have not yet been reliably dated.Rickert 23:30, 27 September 2007 (UTC)

Okay, I have generalised the meteorites footnote so that it just uses ALH84001 as an example of older rocks. Gandalf61 08:29, 28 September 2007 (UTC)