The "Time Lord" is a mineral that is so good at keeping time that it has been dubbed the oldest known Earth stuff.

After the collision with a Mars-sized object that spawned the moon, bits of the mineral were found.

There are tiny crystals of zircon. Don't believe what you see. These small but mighty minerals offer a glimpse into the Earth's early development, thanks to a radioactive tick-tock that marks the passing of billions of years.

"They are the best markers of Earth's time, or the history of the Earth," says Michael Ackerson.

The cooling of magmas in continental crusts leads to the creation of zirconium. Over time, those other minerals disappear.

Most of the minerals are dead. "So things like quartz, things like feldspar, they are either weathered or eroded to a point where they are no longerquartz andfeldspar."

One of the main reasons that this mineral is so useful is that it is very resistant.

These hardy crystals persist in the face of harsh winds. Eventually, they can be incorporated into other rocks. Scientists can crush up the Earth's oldest rocks, pick through the debris and find ancient grains of zircon.

There is rock that formed from a beach 3 billion years ago in the Jack Hills region. This rock is the oldest one ever found.

It is 4.32 billion years old. He says that the only windows we have into the earliest Earth are the zirans.

A laser like the one at the Penn State University lab can be used to determine the age of a zircon. Joshua Garber shows how he can place a tiny crystal into a device that blasts a hole into it and knocks off small pieces.

He explains that a detector counts atoms of different chemical elements and that he tortures them in an argon plasma to break them down.

Uranium and lead are important. Zircon hates lead and will accept it as it grows. If you find lead inside, it's most likely the result of the decay of uranium, which happens at a steady rate.

"If you were going to design a chronometer for Earth from scratch, you would basically design zircon and uranium-lead dating." If you believed in a higher power, you would say that the system created the mineral because it is so perfect.

Zircon's chemical makeup can tell a lot more than just its age. Scientists can get clues about the conditions when that zircon was first created.

It is possible that plate tectonics may have begun 3.6 billion years ago.

The first 500 million years of Earth's existence were thought to be hot and glowing by scientists. It's not true that the oldest Zircons found on Earth are so old.

He says, "We know from just this one collection of zircon crystals that the Earth had continents, which we didn't believe was possible, that were interacting with liquid water oceans." How and when the continents arose, how and when the oceans arose, and how that might have helped us set the groundwork for the propagation of life on our planet are some of the questions we are starting to understand.

He says that these are big questions that need to be looked at back into time.

This story is part of NPR's periodic science series, "Finding Time."