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The Spring 2011 issue of The Earth Scientist is focused on modernizing seismology education. Thanks to IRIS, you can download this issue for free as a pdf. Print copies are available in our online store.

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Image from: Rick Kohrs, Space Science and Engineering Center, University of Wisconsin, Madison

Surface of the Earth

Most of the Earth's surface (70%) is covered with water, and the remaining 30% is taken up by the seven continental landmasses. However, underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava at the surface cooled 4.5 billion years ago.

The crust is broken into many large plates that move slowly relative to each other. Mountain ranges form when two plates collide and their edges are forced up. In addition, many other surface features are the result of the moving plates. The plates move about one inch per year, so millions of years ago the continents and the oceans were in different positions. About 250 million years ago, most of the land was connected together, and over time has separated into seven continents.


Last modified September 6, 2002 by Lisa Gardiner.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF