It was the last period of the Precambrian's Neoproterozoic Era.Multicelled organisms first appeared during this time. Pleistocene (Greek pleistos = most) (popular name: Ice Age).For example, dinosaur fossils are only found during the Mesozoic era some 245 to 65 million years ago. The period of time, also known as an eon, between the end of the Precambrian and today, The Phanerozoic begins with the start of the Cambrian period, 544 million years ago.It encompasses the period of abundant, complex life on the Earth.Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.
Our Earth acquired its present size, more or less, between 4 billion and 5 billion years ago.Throughout the history of life, different organisms have appeared, flourished and become extinct.Many of these organisms have left their remains as fossils in sedimentary rocks.By assembling all these layers together, scientists have worked out what is known as the stratigraphic column or record of the various ages of rock.This record spans the 4.6 billion year record of Earth's history.Geologic time spans are considerably more difficult to comprehend than historical time spans because they are so incredibly long.