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
Old Rocks Give New Clues about Ancient Earth!
News story originally written on July 11, 2002
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!
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
The Archean is the name of the age which began with the forming Earth, as illustrated in this picture. This period of Earth's history lasted a long time, 2.8 billion years! That is more than half the...more
The main force that shapes our planet’s surface over long amounts of time is the movement of Earth's outer layer by the process of plate tectonics. This picture shows how the rigid outer layer of the...more
It was another exciting and frustrating year for the space science program. It seemed that every step forward led to one backwards. Either way, NASA led the way to a great century of discovery. Unfortunately,...more
The Space Shuttle Discovery lifted off from Kennedy Space Center on October 29th at 2:19 p.m. EST. The weather was great as Discovery took 8 1/2 minutes to reach orbit. This was the United States' 123rd...more
A moon was discovered orbiting the asteroid, Eugenia. This is only the second time in history that a satellite has been seen circling an asteroid. A special mirror allowed scientists to find the moon...more
Will Russia ever put the service module for the International Space Station in space? NASA officials want an answer from the Russian government. The necessary service module is currently waiting to be...more
A coronal mass ejection (CME) happened on the Sun early last month. The material that was thrown out from this explosion passed the ACE spacecraft. The SWICS instrument on ACE has produced a new and very...more