About 35 million years ago, an asteroid struck the ocean off the East Coast of North America, leaving behind a massive impact ...

They are significantly older than the rest of the sample material. During their formation, zircon crystals incorporate uranium but reject lead. Over time, the radioactive uranium decays into lead.

To have enough uranium, however, the researchers needed the mineral zircon, which is scarce in basalts that cooled quickly. Turning to new sources, the researchers found zircon in soil deposits ...

To nail down when this happened, Barboni and colleagues examined fragments of the mineral zircon brought back from the moon by the Apollo 14 astronauts. Relative amounts of uranium and lead as ...