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Children's LiteratureAlmost five billion years ago, our Solar System was formed by swirling clouds of dust and gas. Our Earth was also formed in same way. The layers of the Earth are the inner core, outer core, mantle, crust and atmosphere. The Earth's crust is not one solid shell. It is broken into many pieces called plates. They are moving slowly and steadily, constantly changing the surface of the Earth. Some scientists believe that 200 to 300 million years ago the Earth had one super continent, Pangea. Pangea slowly drifted apart. Volcanoes exist where two plates collide or where they overlap each other. Most of the ocean floor beneath the Pacific is one big plate. All around its edge are volcanoes and earthquakes. The Earths atmosphere has also changed over time. At first it was made up of nitrogen and carbon dioxide. As simple life forms developed, the carbon dioxide was changed into oxygen. The presence of oxygen made it possible for people and animals to breathe and evolve. The title is part of the Isaac Asimov's "21st Century Library of the Universe: The Solar System." This collection of books is well written with a large number of photographs and illustrations. The text is direct and addresses questions student are likely to have about the subject matter. 2004 (orig. 2002), Prometheus Books, and Ages 8 to 11.