Talk:Oldest dated rocks
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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) Some sites you can't trust? — Preceding unsigned comment added by 188.8.131.52 (talk) 17:08, 15 January 2014 (UTC)
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)
I mean, seriously, Earth is like one big rock, right? So isn't the inner core the oldest rock? Hananoshi 13:14, 24 August 2008 (UTC)
A misnomer indeed. Should be something like oldest dated rock outcrop or rock outcrop with oldest radiometric age. Seems as the name is a bit lacking in clarity - how about a rename? Vsmith (talk) 00:06, 25 August 2008 (UTC)
- OpposeDo people really consider the inner core when they talk about rock? I tend to think they consider the stuff on the surface. Enlil Ninlil (talk) 09:48, 25 August 2008 (UTC)
- Support Oldest dated rock, or something similar. Viriditas (talk) 14:02, 26 December 2009 (UTC)
Shouldn't the rocks on earth section (or some other part of the article) make mention of the Apollo moon rocks? They're much older than the oldest terrestrial rocks, and they're on earth now. Maybe a section on non-terrestrial rocks? 184.108.40.206 (talk) 01:38, 17 January 2009 (UTC)
Quebec "Oldest Rock"
Was dated with Samarium-Neodymium,
which has a closure temperature high enough that it could have stayed a melt for much longer before it solidified. Also, I'm going to check the references, but I believe that the scientific article talking about this date showed much less clear results than the newspapers were led to believe, and that the U-Pb dates were younger than 4 Ga. I'll get back to this. Awickert (talk) 21:20, 31 January 2009 (UTC)
- Yes, I looked into this, Sm-Nd gives the model age of extraction from the mantle, but it could have resided in a magma chamber for a long-long time. Comparing Sm-Nd with U-Pb is apples and oranges, and from what I hear from geochronologist pals, the U-Pb date of the rock is less than the 4.03 Ga Acasta Gneiss. Will fix with references. Awickert (talk) 17:36, 22 March 2009 (UTC)
- Awickert, I think that in the context of 4031 Ma (+/- 3Ma) vs 4280 Ma (+/- 53ma), this is a substantial amount of time for a melt to remain unsolidified for this reading to be inconclusive. Typically, one would envisage a magma episode to remain molten for much less than 193 Ma (the difference between the 95th percentile age determination maxima for the Acasta reading and the 95th percentile minima for the other reading). Therefore, I would advise you to leave the article as is, and leave this debate up to the boffins; if your geochronologist pals can provide you with a age date on the zircons from the faux-amphibolite which is verifiable, please provide this here on the discussion page so we can agonise over it.
- The other point to make is that the mantle extraction age is a reasonable proxy for the age of formation of this rock. Look at it like this: the rock represents material extracted from the mantle - to the crust. Therefore it is reasonable to imply that upon its removal from the mantle via melting it move upwards (as all other melts have done for 4.66Ga) and eventually became a solid rock. The geochronometer, if not reset, is therefore an accurate measurement of the age of formation of the rock. The zircon U-Pb (let alone the wholly unreliable U-Pb whole rock date) could likely be less accurate a measurement of the initial formation of a crustal rock simply from the first blush of metamorphism >193Ma after the formaion of the rock. Ergo - leave it as it is. Cheers, Rolinator (talk) 02:02, 23 March 2009 (UTC)
- Yeah - I know some people who work in the area. The U-Pb date (as of yet unpublished) was done last fall, and I was told it was closer to the 3.8. I agree - that is a long time for it to be in melt, and the zircon clock could have been reset if T was very high. On the other hand, it seems weird to compare a model age for melt extraction, on one hand, with a U-Pb in zircon on the other hand. If you want me to revert some stuff until I get a better reply, let me know and I will. I'll write here when I get more info. (And off-topic, but thanks for your big edits on exploration geophysics and cumulate rocks.) Awickert (talk) 03:07, 23 March 2009 (UTC)
- Got more info. This isn't published yet, as the work is ongoing. The rocks in the area where the 4.2 Ga rock was found have generally been constrained at the 3.8-ish range. The data show that it is likely that the 4.2 Ga rock was extracted from the mantle and turned into a basalt at 4.2 Ga. However, it seems that it was then re-melted, recrystallized, (maybe some erosion and deposition - memory failing me), and then metamorphosed to amphibolite facies. No zircons exist in the rock for U-Pb dating. So the scientists I talked to said that it isn't the oldest rock because it was re-melted after 4.2. Hope this helps - I might re-add some of the stuff about the rock that I removed, and I'm going to wait for this stuff to be published. Awickert (talk) 06:33, 15 April 2009 (UTC)
Can any body find the correct wiki article that describes the method for dating the crystals? Has it to do with the decay of uranium? A link, note or paragraph would be good. Ctbolt (talk) 12:29, 25 March 2012 (UTC)
- See Zircon#Radiometric_dating and links therein. And, yes uranium it is. Vsmith (talk) 13:40, 25 March 2012 (UTC)
Removed from lead
I've removed the following as it contains innaccuracies and over generalizations from the referenced article.
- A 2012 report in a reliable publication stated a previous flaw in the dating of geological material, with the result of all prior dates being incorrect by 20 to 80 million years and by another method 70 million, such that the rocks of study are, in fact, younger than thought previously. <ref>03 April 2012 L Grossman [http://www.newscientist.com/article/mg21428594.800-age-of-oldest-rocks-off-by-millions-of-years.html New Scientist ] Retrieved 2012-05-06</ref>
The referenced New Scientist article discusses two specific dating techniques. The samarium-146 method was found to heave a discrepancy due to a new half life determination - using the revised HL the dated material "formed 20 million to 80 million years earlier than thought". The second involved uranium isotope ratios for which the suggested discrepancy amounted to rocks previously dated at "4.4 billion years old are now younger by 700,000 years". That would mean the 4,400,000.000 year age would be 4,399,300,000 years which rounds to the stated precision of 4.4 bya. Vsmith (talk) 14:04, 22 July 2012 (UTC)