16.10: Cenozoic Plate Tectonics
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How does the Cenozoic end?
We don't know how the Cenozoic ends. We're still in it! The Cenozoic has been going on for 65 million years. Toward the very end of this time, humans evolved. We are now witness to the geology of the Cenozoic. What came earlier in this era looks a lot like what is going on now.
The Cenozoic began around 65.5 million years ago. We say that it begins after the Cretaceous extinction. We are still in the Cenozoic today. The Cenozoic accounts for only about 1.5% of Earth’s total history. But since it's the the most recent era, it is the one we know the most about. Much of what has been discussed elsewhere in this text describes the geology of the Cenozoic. A few highlights are mentioned here.
The plate tectonics of the Cenozoic are still going on today. Early in the Cenozoic, blocks of crust uplifted to form the Rocky Mountains. Subduction off of the Pacific Northwest formed the Cascades volcanic arc. Crust is being pulled apart to form the Basin and Range province that centers on Nevada.
Evolution of the San Andreas Fault
The San Andreas Fault is where the Pacific and North American plates meet (Figure below). How did the San Andreas Fault form? The Farallon Plate was subducting beneath the North American Plate. This began about 30 million years ago. By 20 million years ago, the Pacific Plate and East Pacific Rise spreading center had started to subduct. This split the Farallon Plate into two smaller plates. The plates started a transform motion where the Pacific and North American plates meet. This formed the San Andreas Fault. The fault moved inland.
This figure shows the evolution of the San Andreas Fault zone from 30 million years ago (bottom) to present (top).
Most Cenozoic plate tectonic activity involves continents moving apart. But smaller regions are coming together. Africa collided with Eurasia to create the Alps. India crashed into Asia to form the Himalayas.
The Pleistocene ice ages began 2.6 million years ago. Glaciers advanced and retreated four times (Figure below). During the retreats, the climate was often warmer than it is today.
Glacial ice at its maximum during the Pleistocene.
These continental ice sheets were extremely thick, like the Antarctic ice cap is today. The Pleistocene ice ages guided the evolution of life in the Cenozoic, including the evolution of humans.
- During the Cenozoic, Pangaea began to split up.
- Subduction of the Farallon plate has resulted in the formation of the Rocky Mountains and the San Andreas Fault.
- The Pleistocene was marked by four advances of ice. The remnants of the last advance of glaciers are found today.
- Why do we know so much more about the Cenozoic than the other eras of geologic time?
- How do plate tectonics processes explain the Rocky Mountains? The San Andreas Fault? The Himalayas?
- What were the Pleistocene ice ages? What did the ice ages do to the evolution of life?