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9.4 The Evolution of Earth



The Pleiades - a star cluster about 400 light years away from Earth.  It is also known as Subaru or The Seven Sisters.  Many of the stars are extremely luminous, very hot blue stars.   [http://apod.nasa.gov/apod/ap130918.html]   


INTRODUCTION

Earth is extremely old - about 4.54 billion (+/- 50 million) years old.   The Universe is 3 times older - 13.798 billion (+/- 370 million) years old, when the expansion known as the Big Bang occurred.  It has evolved to the present stage but it continues to change with stars being born and dying.  (The stars in the Pleiades are only about 100 millions years old.)

The Earth has also undergone an enormous degree of change since it first formed.  The length of the day, year and month have all changed.  The distance to the Sun and Moon and the brightness of the Sun are all different now.   Most important for this topic, is that the shape and distribution of the continents is much different and is constantly changing.

In this unit we will consider the theories about how these things have happened but the emphasis is on how the discoveries have been made.   After all, science is about discovery - not just a collection of “facts”.


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