quote:... It's a zircon, from the Persian word "zargun" meaning "golden colored," an extremely durable mineral found all over the world. This one turned up in a dry, hilly region of Western Australia. It was sitting inside a larger rock, and when scientists checked, it turns out this little grain formed around 4.4 billion years ago. That would make it the oldest rock we've ever seen on this planet, old enough to know secrets about early Earth, old enough to tell us a little something about how life started here.
After all, this planet, geologists say, is only 4.5 or 4.6 billion years old. So this little grain has been around since almost the beginning but not quite.
When geochemists Bruce Watson and Mark Harrison looked more closely at this grain, they could see where it "started." Crystals are minerals that grow, or harden from a hotter, liquid state, and this crystal got its start on the lower left, in the spot marked "core."
Geochemists know that zircons will grab more titanium when it's hotter, less titanium when it's colder, so if you count your titanium concentrations, you can figure out how hot it was when the rock formed: X amount of titanium, for example, means it was 600 degrees Celsius when it grew; Y amount of titanium means it was 350 degrees Celsius. Scientists call this equation "the titanium thermometer."
So Watson and Harrison counted titanium concentrations in a bunch of these very old zircon grains, matched them to the thermometer, and discovered that when these zircons formed, the temperatures ranged from about 680 degrees Celsius, plus or minus 20.
Rocks that crystallize at these temperatures have been exposed to water. This is something geologists know. ...
So, all of a sudden, here was evidence that the red hot, lava-laced, boiling, lifeless Earth of 4.4 billion years ago had water on it! What's more, Watson says, "we feel our results point more strongly toward the idea of surface water."
Here's why: It is now possible to imagine that life began on Earth almost as soon as the Earth began that life (in the presence of water) is, if not inevitable, at least very insistent. Once you've got a planet with water BINGO!
If that's true, chances for life in the universe suddenly improve dramatically.
Here on Earth, life could have formed, been blown away, then formed again and one of those times, down at the bottom of some temporary ocean, sitting by a warm vent it stayed.
That's what this teeny chip of a rock is now allowing us to think: that life has such potency, such urgency, that as soon as life is possible life happens!
That's a mighty big story to find in a pebble.
Hyperbole slightly over the top, but cool info eh?
That is all interesting and mostly true. This is just a minor point, but a rock is not a single grain that is made of one mineral like zircon. That picture is of a grain of the mineral zircon. The rock that it was found in is probably not 4.4 billion years old; the zircon grain is. In order for the rock to be that old, it would have to be totally of an igneous nature. In all likelihood, the rock is a metasedimentary rock that first incorporated the zircon in a sedimentary layer and later underwent metamorphism to produce the rock we see today. If there is an igneous intrusion in the hill that the rock was found in, we can have an idea when the metamorphism took place that actually produced the rock they found.
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For Admin: Who cares if this is off topic, I don't.
Pb will not fit in this crystal structure. Suppose our little zircon has lead in it, where do you suppose it came from?
A possibility that had occurred to me, however I would still like to see it from the scientists that did the paper.
I think he/she is saying that the lead could only come from radioactive decay, which is the mainstream view.
There is, of course, a really weentsy amount of lead mechanically trapped as the crystal grew around them (or whatever). That has a different isotopic composition than radiogenic lead and some other detectable properties, so correcting for "common lead" is very common ;-), and changes the raw date by a fraction of a percent or so. Buth these days the bleeding edge is sub-1% accuracy and every little bit of improvement is just that little bit of improvement more.