The oldest known rocks on Earth are found in the Jack Hills region of Western Australia. These rocks are zircon crystals and are estimated to be 4.4 billion years old.

Here's why these zircon crystals are so important:

* Age: They predate the oldest known intact rocks by hundreds of millions of years.

* Information: The crystals contain tiny inclusions of other minerals that provide clues about the early Earth's environment, including the presence of liquid water.

* Significance: These zircons give us a glimpse into the very early Earth, a time when the planet was still forming and undergoing intense volcanic activity.

While these zircons are the oldest known *rocks* on Earth, it's important to note that they are not the oldest *materials* on Earth. Scientists believe that some meteorites found on Earth are older than the Jack Hills zircons.