Geologic Time Line
Paleontologists and geologists study fossils and rock layers to learn about ancient environments and the organisms that inhabited them. Over the last two centuries a great deal of worldwide research has gone into creating a Geologic Time Line. This has enabled scientists to place dinosaurs into Earth’s history.
Earth’s Geologic Time Line begins with the formation of the planet about 4.6 billion years ago and continues through present time. The largest subdivisions of geologic time are Eras. The three eras most often studied by paleontologists are:
| Paleozoic Era (Ancient animals) |
Began 542 mya
Ended 251 mya
Lasted 291 million years |
- Corals, fish, trilobites, mollusks and coal swamps were some of the dominant environment and life forms of this era.
- At the end of the Paleozoic Era a mass extinction of 95% of all species occurred.
|
Mesozoic Era (middle animals) |
Began 251 mya
Ended about 65 mya
Lasted 186 million years |
- During this time dinosaurs flourished. They differentiated, expanded their range, and diversified into a wide variety of types. They became dominant land animals.
- Mammals, birds, and flowering plants began to evolve.
- The Mesozoic Era ended in another mass extinction, killing about 75% of all species.
|
Cenozoic Era (recent animals) |
Began 65 mya and continues today |
- The Cenozoic Era is the age of mammals.
- Flowering plants (angiosperms) spread around the world.
|
|
