19.3: Life of the Phanerozoic Eon
- Page ID
- 5605
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Does this look like a creature from Earth you know?
It's not hard to take a field trip to see some ancient life. Horseshoe crabs live along the east coast of the United States and elsewhere. These ancient creatures have been more-or-less unchanged for the past 450 million years. This is indicated by fossils. That doesn't get them quite back to the beginning of the Paleozoic but close. So hundreds of millions of generations of horseshoe crabs have seen most of the Phanerozoic go by.
Phanerozoic Eon
The Phanerozoic Eon is divided into three eras—the Paleozoic, the Mesozoic, and the Cenozoic (Figure (below). They span from about 540 million years ago to the present. We live now in the Cenozoic Era.
Earth’s climate changed numerous times during the Phanerozoic Eon. At the end of the Precambrian, much of the planet was covered with glaciers. At the start of the Phanerozoic Eon, the climate became warm and humid. Since then Earth’s climate has gone through four cycles of frigid glaciers and warm tropical seas. Some organisms survive changes in the climate. Others go extinct when the climate changes too much.
Phanerozoic Time Line
Table below shows some of the life forms that developed during the Phanerozoic Eon. Life gradually became more diverse and new species appeared. Most modern organisms evolved from species that are now extinct.
| Era | Millions of Years Ago | Major Forms of Life |
|---|---|---|
| Cenozoic | 0.2 (200,000 years ago) | First humans |
| 35 | First grasses; grasslands begin to dominate the land | |
| Mesozoic | 130 | First plants with flowers |
| 150 | First birds on Earth | |
| 200 | First mammals on Earth | |
| 251 |
Age of dinosaurs begins |
|
| Paleozoic | 300 | First reptiles on Earth |
| 360 | First amphibians on Earth | |
| 400 | First insects on Earth | |
| 475 | First plants and fungi begin growing on land | |
| 500 |
First fish on Earth |
Summary
- The Phanerozoic has spanned from 540 million years ago to present.
- The Phanerozoic Eon is made up of the Paleozoic, Mesozoic, and Cenozoic Eras.
- The quantity and diversity of life has exploded since the beginning of the Phanerozoic.
Review
- When did the Phanerozoic begin? When did it end?
- What are some of the major events that have occurred in the Phanerozoic?
- What eras make up the Phanerozoic?