of the Earth
Kevin C. Hartzog
Geologic Time Scales
Eras of the Earth
Paleontologist have divided Earth's history into eras, periods, and epochs.
Monumental events and changes mark the end of one time frame, and the
beginning of another. The Precambrian
is the first time frame in Earth's history, begining with the birth of
the Earth, and ending with an event called the "Cambrian Explosion".
An abundance of diverse life found in the Burgess Shell marks the Cambrian
Explosion. This explosion was latter seen to be less of a sudden increase
in families, and marked more by extraordinarily good conditions for the
formation of fossils. Still, that early exclamation still lives with us
today. The Cambrian Explosion begins the
Paleozoic Era which saw the evolution of mulicellular organisims,
and the evolution of shells. The Paleozoic Era ended with a mass exticntion
caused by the impact of a comet or asteroid 250mya. The exit of the Paleozoic
Era herladed the begining of the The Mesozoic Era, which saw the rise
and fall of the dinosaurs. Both dinosaurs and the Mesozoic Era ended when
another comet struck the Earth 65mya. This event rose the curtain on the
Cenozoic Era, the age of mammals, birds, bony fish, and flowering
plants.What event will end the Cenozioc?