Page 18 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

Origin of life

Introduction Life on Earth began at least 3.5 billion years ago, and possibly
more than 4 billion years ago. These oldest-known life forms
were microscopic single cells that lived in water—tiny capsules

of watery fluid containing the complex chemicals vital to all
types of life. How these cells formed is still not known, but the
process was probably fueled by the heat and chemical energy
of hot springs, either on land or on the deep ocean floor.

The impacts generated intense
Early Earth heat—for much of its early life, the
Planet Earth was formed from the rock and dust planet was a ball of molten rock.
that orbited the newly formed Sun. As the planet
grew in size, its gravity attracted more rocks and
comets, which contained water and the chemical
elements needed for life. All the rocks impacting
the growing planet made it heat up until it melted.
Later, the planet cooled enough for liquid water to
settle on the surface. Even today, liquid water is
vital to all forms of life.

The early Earth’s surface
was bombarded by giant
lumps of space rock.

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