The Earth is 4.54 billion years old. We know that not from radiometric dating of rocks on our planet, as the oldest rocks haven’t yet been found, but from dating meteorites that fall on earth from the solar system, which formed around the time Earth did.
But of course that’s not fodder for creationist, for we also have old homegrown rocks, clearly showing that the earth is far older than, say, 10,000 years.
And now we’ve found the oldest bit of Earth yet. As ZME Science and a new paper reported yesterday, it’s a zircon crystal from Australia dated at 4.37 billion years. The paper with the original report is in Nature Geoscience (reference and link below; free download [I think]).
Here it is.
And it’s not big:
The geological relic indicates, for one, that Earth’s crust formed shortly after the planet stabilized and formed. John Valley, a University of Wisconsin geoscience professor who led the research, said the findings suggest that the early Earth was not as harsh a place as many scientists have thought.
No doubt, this is an extraordinary find, however, the untrained eye would have surely missed it. Measuring about 200 by 400 microns, or roughly two times the width of a human hair, the tiny gem was luckily retrieved by geologists in 2001 from a rock outcrop in Australia’s Jack Hills region.
The researchers used two ways to check the date: radiometric uranium-lead dating and atom-probe tomography, which uses the actual position of individual atoms in the crystal to check the accuracy of the U/Pb method. I’ll let the readers enlighten us about how this method works, as I don’t fully understand it myself; but the upshot is that the APT dates comport with the uranium lead dates, making hash of the creationist objection that dating methods are unreliable, even in the hands of experts.
The APT was used because of worries that U-Pb dating might be off because lead might have moved within the crystal. This shows that scientists do know the ways that dating could be off, and have checks for them. And APT showed no evidence of such movement. I’ll show that by simply posting part of the paper’s abstract:
Here we use atom-probe tomography to identify and map individual atoms in the oldest concordant grain from Earth, a 4.4-Gyr-old Hadean zircon with a high-temperature overgrowth that formed about 1 Gyr after the mineral’s core. Isolated nanoclusters, measuring about 10 nm and spaced 10–50 nm apart, are enriched in incompatible elements including radiogenic Pb with unusually high 207Pb/206Pb ratios. We demonstrate that the length scales of these clusters make U–Pb age biasing impossible, and that they formed during the later reheating event. Our tomography data thereby confirm that any mixing event of the silicate Earth must have occurred before 4.4 Gyr ago, consistent with magma ocean formation by an early moon-forming impact about 4.5 Gyr ago
Valley, J. W. et al. 2014. Hadean age for a post-magma-ocean confirmed by atom-probe tomography. Nature Geoscience. doi:10.1038/ngeo2075