RICHARD BIZLEY / SCIENCE PHOTO LIBRARY RICHARD BIZLEY / SCIENCE PHOTO LIBRARY
Formation of the Earth. Artwork sequence showing the stages in the formation of the Earth. At upper left, small fragments of rock and dust accreted and stuck together until the resulting bodies (planetessimals) were large enough for gravity to become the dominant force. From that point on, the protoplanet grew swiftly in size, with impacts turning it molten. At right, the planet became large enough for its own gravity to flatten the surface and retain an atmosphere. The initial formation took place around 4.6 billion years ago. The last two pictures show the formation of the early atmosphere. The final globe shows the ancient continent of Rodinia during the Pre-Cambrian period (650 million years ago).
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