Geologic History

• The theory states that the true age of the earth is about 4.6 billion years old, formed at the same time as the rest of the solar system.
• Scientists determine the age of the rock using radiometric dating method.
• In the very beginning of earth's history, this planet was a giant, red hot, roiling, boiling sea of molten rock - a magma ocean.
• The heat had been generated by the repeated high speed collisions of much smaller bodies of space rocks that continually clumped together as they collided to form this planet.
• As the collisions tapered off, the earth began to cool, forming a thin crust on its surface.
• As the cooling continued, water vapor began to escape and condense in the earth's early atmosphere.
• Clouds formed and storms raged, raining more and more water down on the primitive earth, cooling the surface further until it was flooded with water, forming the seas.
• The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet.
• Most of these life-forms are found as fossils, which are the remains or traces of an organism from the geologic past that has been preserved in sediment or rock.
• The Geologic Time Scale is divided by the following divisions: Eons, Eras, Periods, Epochs.
• Eons: Longest subdivision; based on the abundance of certain fossils.
• Eras: Next to longest subdivision; marked bymajor changes in the fossil record.
• Periods: Based on types of life existing at the time.
• Epochs: Shortest subdivision; marked bydifferences in life forms and canvary from continent to continent.
• Paleozoic: Age of Invertebrates
• Cenozoic: Age of Mammals
• Mesozoic: Age of Reptiles
• The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet. These divisions are called geochronologic units (geo: rock, chronology: time).