This image shows a cross section through the earth’s crust and upper mantle showing lithosphere plates (made of the crust layer and the top part of the mantle) moving over the asthenosphere (upper mantle). Click on image for full size ( 130 KB)

Scientists have found 2.5 billion year old rocks in China that help us understand more about what the Earth was like long ago.

These rocks formed early in Earth’s history, during the Archean Age, when there was no ocean and no continents and Earth was a very hot place. It was not until Earth formed layers and cooled down that plate tectonics started to move giant rocky plates around the surface of the Earth as it does today. Today, plate tectonics is a very important process on Earth, making mountains grow high, volcanoes spew lava and earthquakes rumble. But before plate tectonics started, the world was a very different place.

Scientists have been unsure of when plate tectonics actually began on Earth . Until recently, there wasn’t any evidence that lithosphere plates moved before 2 billion years ago. The Earth was thought to be still too hot for plates to form at the surface and slide on the asthenosphere layer in the upper mantle. However, the 2.5 billion year old rocks found in China tell a different story.

The minerals in the newly found rocks formed in the upper part of the mantle layer, underneath a seafloor. These minerals show evidence that the upper part of the mantle partially melted and then flowed a little bit. When the upper mantle layer does this, plates are able to move at the Earth’s surface. So, these rocks show that the plates of lithosphere were active and sliding around on the upper mantle (the asthenosphere) long before we thought they could!

When plate tectonics is happening, hot volcanic vents often form on the sea floor and these vents may have provided the nutrition and conditions that were needed for the first life to develop and flourish on Earth . Today deep-sea vents provide home and food for many organisms and they may have done so 2.5 billion years ago as well.

This image shows a cross section through the earth’s crust and upper mantle showing lithosphere plates (made of the crust layer and the top part of the mantle) moving over the asthenosphere (upper mantle). Click on image for full size ( 130 KB)

Scientists have found 2.5 billion year old rocks in China that help us understand more about what the Earth was like long ago.

These rocks formed when Earth was young, during the Archean Age. During the Archean, there was no ocean and no continents and Earth was a very hot place. Earth cooled slowly and eventually it was cool enough for part of the upper mantle layer (the asthenosphere), below the Earth’s crust, to flow just a little, moving the giant plates that lie above. This is called plate tectonics and it still happens today. In fact, plate tectonics is a very important process on Earth today, making mountains grow high, volcanoes spew lava, and earthquakes rumble.

When did this important process begin to shape the surface of our Earth ? Scientists have been unsure of when plate tectonics actually began. Until recently, there wasn’t any evidence that plates moved before 2 billion years ago. We thought Earth was still too hot for rocky plates to form at the surface and slide on the asthenosphere. But the 2.5 billion year old rocks found in China tell a different story.

The newly discovered rocks formed long ago in the upper part of the mantle layer, underneath an ancient seafloor. These rocks show evidence that, 2.5 billion years ago, the upper part of the mantle layer would melt a little bit and then flow a little bit. When the rocks in this layer did this, plates could move at the Earth’s surface. So, these rocks show that the plates of the lithosphere were active and sliding around long before we thought they could!

This image shows a cross section through the earth’s crust and upper mantle showing lithosphere plates (made of the crust layer and the top part of the mantle) moving over the asthenosphere (upper mantle). Click on image for full size ( 130 KB)

What was the Earth like a long time ago? To answer this question, some scientists look for very old rocks to find clues. Now they have found rocks in China that are 2.5 billion year old and these rocks have some interesting clues!

These rocks formed during the Archean Age, when the Earth was young. During the Archean there was no ocean and no continents on the Earth. It was a very hot place. After a long time, Earth cooled a bit, and giant plates of rock started to move around the surface of the Earth just like they do today. This is called plate tectonics . Today, plate tectonics is a very important process on Earth. It makes mountains grow high, volcanoes spew lava, and earthquakes rumble.

Scientists want to know when the Earth was cool enough for plate tectonics to begin. They thought that plates started to move about 2 billion years ago. They thought the Earth was too hot for plate tectonics before that time. But the 2.5 billion year old rocks found in China tell a different story.

These rocks formed in the upper part of the mantle layer, underneath a seafloor. They show that a long time ago they used to flow slowly and were able to move the plates of the Earth’s crust that were above them. So, the plates were sliding around long before we thought they could!