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8.27: Climate Change in Earth History

Difficulty Level: Basic Created by: CK-12
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How important was the Pleistocene ice age to human evolution?

Climate is dynamic; climate has changed through Earth history. Climate has changed a lot during the time humans have been evolving. As the climate got colder, people learned to hunt more since plants became scare in the winter. Better hunting required better tools. Better tools helped to spur on the evolution of culture.

How Earth’s Climate Changes

Earth’s climate has changed many times through Earth's history. Over much of Earth’s past, the climate was warmer than it is today. Picture in your mind dinosaurs roaming the land. They're probably doing it in a pretty warm climate!

Dinosaurs thrived during one of the warmest periods in Earth's history.

But ice ages also occurred many times in the past. An ice age is a period when temperatures are cooler than normal. This causes glaciers to spread to lower latitudes. Scientists think that ice ages occurred at least six times over the last billion years alone. How do scientists learn about Earth’s past climates?

The last major ice age took place in the Pleistocene. This epoch lasted from 2 million to 14,000 years ago. Earth’s temperature was only 5° C (9° F) cooler than it is today. But glaciers covered much of the Northern Hemisphere. In Figure below, you can see how far south they went. Clearly, a small change in temperature can have a big impact on the planet. Humans lived during this ice age.

Pleistocene glaciers covered an enormous land area. Chicago is just one city that couldn't have existed during the Pleistocene.

Why Climate Changes

Several natural processes may affect Earth’s temperature. They range from sunspots to Earth’s wobble.

  • Sunspots are storms on the sun. When the number of sunspots is high, the sun gives off more energy than usual. Still, there is little evidence for climate changing along with the sunspot cycle.
  • Plate movements cause continents to drift closer to the poles or the equator. Ocean currents also shift when continents drift. All these changes can affect Earth’s temperature.
  • Plate movements trigger volcanoes. A huge eruption could spew so much gas and ash into the air that little sunlight would reach the surface for months or years. This could lower Earth’s temperature.
  • A large asteroid hitting Earth would throw a lot of dust into the air. This could block sunlight and cool the planet.
  • Earth goes through regular changes in its position relative to the sun. Its orbit changes slightly. Earth also wobbles on its axis of rotation. The planet also changes the tilt on its axis. These changes can affect Earth’s temperature.


  • Earth's climate has been warmer and colder, but mostly warmer, through Earth history.
  • Many natural processes change Earth's climate. These include sunspots, plate tectonics, volcanism, asteroid impacts and Earth's motions.
  • The Pleistocene Ice Age lasted from 2 million to 14,000 years ago. Earth’s temperature was only 5° C (9° F) cooler than it is today.


Use this resource to answer the questions that follow.

The Permian Mass Extinction at http://www.youtube.com/watch?v=hDbz2dpebhQ (9:59)

  1. What were therapsids?
  2. What occurred 250 million years ago?
  3. What did Peter Ward discover?
  4. What happened to world temperatures and what effect did it have on life?
  5. Explain what occurred during the first extinction.
  6. When did the marine extinction occur?
  7. Describe the third phase of the extinction.
  8. What increased between the marine extinction and the final land extinction?
  9. What caused the Earth's temperature to rise by 10 degrees?
  10. How long did it take for life to recover? What animals came to dominate the Earth?


  1. How has climate changed in the past 2 million years?
  2. How can the sun change Earth's climate?
  3. What is an ice age? When was the most recent?

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asteroid A rock that flies through space.
axial tilt The difference between a planet's axis of rotation and plane of orbit.
ice age Period when temperatures are cooler than normal.
sunspot A solar magnetic storm that can affect solar radiation.

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Date Created:
Jan 04, 2013
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Aug 29, 2016
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