What defines the beginning of the Quaternary and the Holocene?
The most recent period of the Cenozoic is the Quaternary, which began about 2.6 million years ago. The most recent epoch is the Holocene, which began around 12,000 years ago. Go back to the lesson on human evolution in Concept Life History to figure out what events mark the beginning of these time periods.
The Cenozoic began around 65.5 million years ago and continues today. Although it accounts for only about 1.5% of the Earth’s total history, as the most recent era it is the one scientists know the most about. Much of what has been discussed elsewhere in Concepts Earth Science describes the geological situation of the Cenozoic. A few highlights are mentioned here.
The paleogeography of the era was very much like it is today. Early in the Cenozoic, blocks of crust uplifted to form the Rocky Mountains, which were later eroded away and then uplifted again. Subduction off of the Pacific Northwest formed the Cascades volcanic arc. The Basin and Range province that centers on Nevada is where crust is being pulled apart.
Evolution of the San Andreas Fault
The San Andreas Fault has grown where the Pacific and North American plates meet. The plate tectonic evolution of that plate boundary is complex and interesting (Figure below). The Farallon Plate was subducting beneath the North American Plate 30 Ma. By 20 Ma the Pacific Plate and East Pacific Rise spreading center had started to subduct, splitting the Farallon Plate into two smaller plates. Transform motion where the Pacific and North American plates meet formed the San Andreas Fault. The fault moved inland and at present small sea floor spreading basins along with the transform motion of the San Andreas are splitting Baja California from mainland Mexico.
This figure shows the evolution of the San Andreas Fault zone from 30 million years ago (bottom) to present (top).
Although most plate tectonic activity involves continents moving apart, smaller regions are coming together. Africa collided with Eurasia to create the Alps. India crashed into Asia to form the Himalayas.
As the continents moved apart, climate began to cool. When Australia and Antarctica separated, the Circumpolar Current could then move the frigid water around Antarctica and spread it more widely around the planet.
Antarctica drifted over the south polar region and the continent began to grow a permanent ice cap in the Oligocene. The climate warmed in the early Miocene but then began to cool again in the late Miocene and Pliocene when glaciers began to form. During the Pleistocene ice ages, which 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 (Figure below) .
This continental glacier over Antarctica is up to 4,000 meters (12,000 feet) thick.
The Pleistocene ice ages guided the evolution of life in the Cenozoic, including the evolution of humans.
- During the Cenozoic, the crust that had once been joined as Pangaea has mostly been moving apart.
- 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 which are found today.
Use this resource to answer the questions that follow.
1. What are the two divisions of the Cenozoic era?
2. What mountains formed during this time?
3. What was carved out of the Colorado Basin?
4. How much of the land was covered in ice?
5. How did animal populations change?
1. Why did the plate boundary that runs up California change from convergent to transform?
2. How is subduction responsible for the Rocky Mountains, the Cascades and the Basin and Range?
3. What is the history of the advance and retreat of ice during the Pleistocene?