Chapter 10 Geologic Time The Geologic Time Scale

Chapter 10 Geologic Time

The Geologic Time Scale Division of Earth’s history into time units based largely on the types of life-forms that lived only during certain periods p 4 Major Subdivisions: p n n Eons Eras Periods Epochs

Subdivisions of Geologic Time p Eon Longest subdivision in the geologic time scale that is based on the abundance of certain types of fossils Era Second-longest division of geologic time Based on major worldwide changes in types of fossils

Subdivisions of Geologic Time p Periods n p Units of geologic time characterized by the types of life existing worldwide at the time Epochs n n Next-smaller division of geologic time after the period Characterized by differences in life-forms that may vary regionally

Organic Evolution Change of organisms over geologic time p Environmental changes can affect an organism’s survival p n n Adapt or die out Natural Selection Process by which organisms that are suited to a particular environment are better able to survive and reproduce than organisms that are not p Survival of the Fittest p

Chapter 10, Section 2 Early Earth History

Precambrian Time p p The longest part of Earth’s history Includes the Hadean, Archean, and Proterozoic Eons 4. 5 billion years ago to 544 million years ago Cyanobacteria (blue-green algae) is thought to be one of the first living organisms

Paleozoic Era p p Era of ancient life 544 million years ago 248 million years ago Many marine (oceandwelling) fossils have been found during this era Fossils of both vertebrates and invertebrates have also been found

Chapter 10, Section 3 Middle and Recent Earth History

The Mesozoic Era p p p Era of middle life Between 248 and 65 million years ago Marked by rapid movement of Earth’s plates n p p Pangaea (massive landmass) began to brake-up and move Dinosaurs were active during this era Birds, Mammals, Gymnosperms (produces seeds, but not flowers), and Angiosperms (flowering plants) were also present during this era

The Mesozoic Era p p Ended with a hypothesized comet or asteroid collision to Earth causing a dust cloud to block out the sun This resulted in an apparent “great extinction” that killed many of the prehistoric species of living organisms.

The Cenozoic Era p p Era of recent life Began 65 million years ago and continues today Divided into the Tertiary and Quaternary periods Features periods of mountain building