Snowball Earth

The snowball earth theory says that at least once during the earth's history, the entire earth was covered with ice. The end of the last period of world glaciation was 550 million years ago, and marked the beginning of the age of plants and animals. As evidence, scientists have found rocks that look like drop stones in ancient rock layers close to the equator. Drop stones are stones dropped by glaciers when they melt. The snowball earth is fascinating because it says that our planet has gone through extreme climate changes throughout its history.

Usually we say that Venus, which is about the same size as earth and is closer to the sun, is "too hot" for life to exist. Mars, which is smaller than the earth and farther way from the sun, is "too cold." The earth is "just right."

However, the snowball earth theory says that every planet is constantly subject to tug of war between the frozen cold of space and the inferno of magma within.

• The temperature on the Earth's surface is the result of many factors:
• The shape and location of the continents
• The amount of CO2 in the atmosphere
• The reflective properties of the surface - water, snow, rocks, plants

 The following three BBC videos explain the evidence for Snowball Earth. It is an exciting story of scientific detective work, and how scientists build on the work of others to better understand our past and our future.