After digging through lunar samples brought back by astronauts, scientists were surprised to find what could be Earth's oldest rock.
"It is an extraordinary find that helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life", said Dr. David Kring, co-author of the new study and a researcher at the Lunar and Planetary Institute (LPI).
An worldwide team of scientists found a tiny fragment - weighing less than an ounce - composed of quartz, feldspar and zircon in one of those moon rocks, according to a news release about the discovery.
Curtin University research into lunar rock samples retrieved by astronauts nearly 50 years ago has found one of the samples may be originally from Earth, thrown into space when an asteroid struck our planet billions of years ago. Once the sample reached the lunar surface, it was affected by several other impact events, one of which partially melted it 3.9 billion years ago, and which probably buried it beneath the surface.
This theory is the easiest explanation since the formation of such a fragment would need an oxidizing environment. He holds a B.A.in Psychology from the University of Toronto, and a Master of Science in Public Health (M.S.P.H.) from the School of Public Health, Department of Health Administration, at the University of North Carolina at Chapel Hill.
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The fragment of Earth was blasted off the planet during a powerful impact some 4 billion years ago, researchers said.
To have a lunar origin, the rock would have had to crystallise at tremendous depth where rocks tend to have very different compositions, they write.
This rock, along with other lunar samples, was lying at the Lunar Curation Facility at the Johnson Space Center in the United States. Impact craters, some flooded by shallow seas, cover large swaths of the Earth's surface. Then, a massive collision between Earth and a comet or asteroid threw the rock to the Moon. Therefore, the simplest interpretation is that the sample came from Earth. This stone was blended with other lunar surface materials along these lines into one example.
There, Apollo 14 crew member Alan Shepard collected the rock, designated it as 14321 and brought it back to Earth.
Reference: "Terrestrial-like Zircon in a Clast from an Apollo 14 Breccia", J. J. Bellucci et al., 2019 January 24, Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2019.01.010, https://www.sciencedirect.com/science/article/pii/S0012821X19300202].
By contrast, the terrestrial conditions seem much more likely - even if it seems a spectacular coincidence that this tiny fragment was later returned to Earth.
Once that information sinks in, imagine how the trajectory of the rock billions of years ago when asteroids hit our planet.