The time-lords are named Zircon. They are able to track events in deep time that would otherwise be lost because they are so strong.

Sarah McCAMMON is the host.

About 4 1/2 billion years ago, the Earth was very young. Scientists use a mineral that serves as a perfect geologic clock to learn about its earliest history. The mineral that's been called the time lord is part of our series.

The mineral is called zircon. The synthetic diamond look-alike, zircon, is not to be confused with the real thing. It could be either red or golden. The National Museum of Natural History has some big ones. They are near the Hope Diamond.

These are pretty Zircons, that's what Michael Anderson says. These are zircons that are clear and have a color that makes them look gemstones.

Michael Ackerson is a geology professor. The ones in his office are very small. They look like sand. I can see them under the microscope.

This is a microscope. If I can do this, let me do it. I don't want to look through microscopes. Okay, let's get on with it. It's my goodness. What is that looking like?

Anderson said yes.

They appear to be little diamonds or something. They were not going to be pretty.

ACKERSON: That's right.

One of the crystals I'm looking at is 4.32 billion years old, according to him. The oldest pieces of earth still exist today, and they are called zircs. It goes back as far as 4.37 billion years.

Anderson says that they are the best markers of Earth's time.

A zircon crystal is formed in molten rock. Minerals do as well. A granite mountain that slowly weathers away will be made up by them

Most of the minerals are dead. They're no longer quartz and feldspar because they're no longer weathering. One of the reasons that zircon is useful is that it is very resistant.

The hardy crystals are incorporated into another rock as it forms. Scientists can crush up the Earth's oldest rocks and pick through the debris to find older ones. They zap it with a laser to find out its age.

Joshua Garber is in the lab. The instruments that we used to date are in this corner.

There is a machine at Penn State that blasts off small pieces.

They're going to be broken down into their smallest components by torture. I measure the number of atoms at the end of the experiment.

The important atoms are lead and Uranium. There is a growing crystal of zircon that will accept the radioactive substance. zircon doesn't likelead. If you find lead inside, it's most likely the result of the decay of uranium, which happens at a steady rate.

He is a geology student at Penn State. It's almost as if they were designed to be timekeepers.

If you believed in a higher power, you would say, "Oh, the higher power created this mineral with this particular system because it is so perfect for Earth."

If you look at the chemical makeup of a zircon, you can see more than just its age. Scientists can get clues about what the conditions were like when that zircon was created. The first 500 million years of the Earth's existence were thought to be hot and glowing. It's not true that the oldest Zircons found on Earth are so old.

We didn't think it was possible for the Earth to have continents and interact with liquid water oceans.

He says tiny zircons allow us to explore big questions about how our planet's early years set the stage for life.

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