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THE TREE OF LIFE
Life on our planet comes in many shapes and sizes-ranging from the familiar to the
bizarre. For centuries, scientists divided the living organisms into two groups-plants
and animals. During the last century, scientists have reconsidered how Earth's life
forms should be grouped. In part because of discoveries made in Yellowstone, scientists
have proposed a "Tree of Life" that divides all living things into three separate branches
or domains, Eukarya, Bacteria, and Archaea. Plants and animals are now only allotted a
small space in Domain Eukarya.
The Tree of Life is based on differences in DNA, or deoxyribonucleic acid, and each domain
represents life forms that are fundamentally different from those in the other two.
Scientists think the prokaryotic organisms that comprise Domains Archaea and Bacteria
shared common ancestry billions of years ago and were likely the earliest life forms on
the Earth. Domain Eukarya branched off from Archaea.
Scientists have proposed that the most primitive life forms and the descendents of
Earth's earliest organisms would be found in environments similar to those that existed
on a young, hot planet. The "universal ancestor" to all life on Earth may exist in the
hydrothermal areas of Yellowstone.
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