To peer into Earth’s deep time, meet a hardy mineral known as the Time Lord

The oldest known Earth stuff that remains on the surface of our planet is a mineral that’s been called the “Time Lord” because it’s so incredibly good at keeping geologic time.

The mineral is zircon, and scientists have found bits of it that formed 4.37 billion years ago, not too long after the proto-Earth's epic collision with a Mars-sized object that spawned our moon.

Tiny crystals of zircon can look like sand, or useless crud. But don't be fooled. With a radioactive tick-tock that marks the passing of billions of years, these small but mighty minerals offer us a peek into the Earth's early development.

"They are really the best markers of Earth's time, or the history of the Earth," says Michael Ackerson, a geologist with the Smithsonian's National Museum of Natural History.