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Appears that a 4.4 billion-year-old crystal is oldest piece of Earth, and the crystal's chemistry -- specifically, the ratio of oxygen isotopes within it -- suggests that the temperatures on Earth 4.4 billion years ago would have supported liquid water, and therefore perhaps life; Earth is 4.54 billion years old.

According to this xkcd comic, "all the crust older than 3.5 billion years has been recycled into the mantle by subduction."


Stratigraphic Record - all the crust older than 3.5 billion years has been recycled into the mantle by subduction.


Is it true that it is possible there is a roughly one billion years of Earth's history with water present that's unaccounted for, and if so, do we have any reason to believe we'll better understand this time in Earth's history?

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    $\begingroup$ Also keep in mind that the vast majority of oceanic crust older than ~200 myr has been subducted as well. The continents preserve a lot of information, but most of the geologic record is destroyed. $\endgroup$ – Joe Kington May 6 '14 at 18:43
  • $\begingroup$ +1 @JoeKington: Awesome, thanks for pointing that out! If for some reason you're able to provide a more complete answer, please feel free to post one and I'll review it. If it's a better answer, I'll change my answer selected to your answer. $\endgroup$ – blunders May 6 '14 at 18:45
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There was an article in that year's Scientific American, which I've read in the Polish edition. I don't have that paper now, but I think this was that one: http://www.scientificamerican.com/article/the-oldest-rocks-on-earth/

The discovery is described in short here: http://news.nationalgeographic.com/news/2014/02/140224-oldest-crust-australia-zircon-science/. It's about Zircon crystals, that are to be 4.4 billion years old. However, as the article states, the found is not (yet?) widely researched. But it's accepted, there are rocks that are 3.8 billion years old.

The problem is, only a special kind of crystals could survive the conditions on the young Earth, and zircons are one of them. They preserve only some part of the information about the geological history of the Earth. So it's not like that, that nothing has survived the first billion years, it's only a special minerals and rock did. It's not enough to answer many questions that are of top importance, like the origins of the life (but probably no geological sources would ever do, because of the fragility of the speculated pre-cellular life forms). However, we do get a lot of valuable information that will allow us to learn many facts about the Earth's history we didn't know before.

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  • $\begingroup$ Thanks. Possible my question is not clear, or I've misunderstood your answer, but "4.4 billion minus 3.8 billion = 600 million" years that are unaccounted for; the rocks in Inukjuak, Quebec in Canada are a very, very small sample of the crust from 3.8 billion years ago; meaning it's unclear what if anything that sample might say about Earth. Gist of the question is there a duration of Earth's history for which we have reason to believe life may have been on Earth, but are unable to account for because "all the crust older than 3.5 billion years has been recycled into the mantle by subduction." $\endgroup$ – blunders May 6 '14 at 14:00
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    $\begingroup$ @blunders Well, yes, we have only a samples, but it's not just that 'everything older than 3.5b was melted'. Those samples are hard to find, and yes, they don't answer all the questions we would have, but there are always more questions to answer than answers to be given. It was not clear what exactly you want to know, but if you mean life, probably we'll never know about its origins on Earth and we'll have to base on speculations only. $\endgroup$ – Danubian Sailor May 6 '14 at 14:07
  • $\begingroup$ Okay, selected your answer as the answer, though it might be of value to edit your answer to directly reflect your understanding of the question based on understanding now. $\endgroup$ – blunders May 6 '14 at 14:10

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