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Precambrian Time is the time period in which the earth
formed and the earliest life began. Information on the
period is sketchy, as no one is sure exactly how the earth
formed. It is most commonly thought that the sun formed in
the center of a spinning cloud of dust. Some of the leftover
dust spun together and formed the planets. No one is sure,
or will probably ever know for sure how the universe began
or how that spinning cloud of dust containing just the right
ingredients for life happened to form and created Earth, a
planet ideal for life.
Also, there is some debate as to how life began. Everyone
is familiar with the creation/ evolution debate, but there
are many debates inside of both of those categories. Some
scientists believe that a giant comet containing the carbon
necessary for life crashed into the planet. Others believe
that the necessary ingredients for life were already on
earth from the beginning and life started quite by accident,
deep in the ocean were the right elements just happened to
collect. Still others believe that an asteroid from another
planet, containing bacteria of some sort, survived the harsh
atmospheric entry process and landed on earth. These people
believe that this bacterium simply multiplied and evolved
into other forms of life. However life may have started, it
did so and that is the important part. Precambrian time
includes the Archean, the
Proterzoic, and the
Priscoan Eons.
The Priscoan Eon began
about 4.6 billion years ago with the formation of the earth.
Geological evidence shows that the earth's crust melted and
hardened many times. Continents took shape and began to
grow. Oceans and atmosphere also took shape in the early
part of this eon. Most of the rocks that formed during this
time were metamorphic. Many great masses of granite were
created. Late in this eon the earliest life formed. It was
simple bacteria and algae. Later, these simple creatures
would evolve into life as we know it.
In between the Priscoan
Eon and the Proterzoic
Eon is the Archean Eon.
During this time life evolved and the planet Earth was
shaped. It was a time of great transition.
The Proterzoic Eon
began about 2.2 billion years ago. During this time many
important things happened to further the evolution of the
earth. Increasingly more complex creatures formed. The first
life forms to be considered animals formed in rocks about
700 million years ago. These animals included worms, jelly
fish, corals, as well as many other
primitive invertebrates. Plants also appeared and
evolved.
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