This date comes from analysis of zircon crystals found in Western Australia. Zircon is a very durable mineral, and these particular crystals are the oldest known Earth materials.

It's important to note that this doesn't mean there wasn't rock present before that. Earth is estimated to be around 4.54 billion years old, and it's likely that rocks existed during those early years. However, they were likely recycled and destroyed by the intense heat and volcanic activity of the early Earth.

So, while we can't date rocks from that time period, the oldest rocks we have provide a glimpse into the early history of our planet.