Shop Windows to the Universe

Please help support Windows to the Universe, and our activities to help Earth and space science teachers, with a tax-exempt donation today!
There are two ideas about how glaciers formed on Earth between about 717 and 630 million years ago – a time known as “Snowball Earth”. The idea that at least two long glaciations happened during which communication between the ocean and the atmosphere was cut off (described in the top half of this image) is more likely based on the evidence we have today. In this scenario, the Earth was ice-free at 670 and 630 million years ago because carbon dioxide built up in the atmosphere.
Click on image for full size
Credit: Zina Deretsky, National Science Foundation

Scientists Find Signs of “Snowball Earth” Amidst Early Animal Evolution

There used to be sea ice floating on the tropical ocean, according to new evidence found by geologists. This was quite a long time ago, 716.5 million years ago, during a time known as Snowball Earth.

This chilly time was among the greatest ice ages known to have taken place on Earth. Ice formed all over the planet, even in the tropics. It was in this frozen world that scientists believe the first animals evolved.

The geologists studied ancient tropical rocks and found evidence that ice was floating in the sea at the time when they formed. These rocks formed in the tropics long ago, but today they are located in a remote area of northwestern Canada thanks to the continent-moving abilities of plate tectonics. Based on magnetic information and the minerals in these rocks, scientists know that they used to be located at sea level in the tropics, just north of the equator.

Of course, scientists can’t find ice preserved in rocks. So how did they figure out that it was icy near the equator? They found evidence of ice in the rocks that is like a footprint that ice used to be there. This evidence includes pieces of rock that have been gouged by glaciers and pieces of rock that were carried out to sea within ice and then dropped to the seafloor as the ice melted.

A world covered with snow and ice must have been a challenging place to live. But life did survive during this time. This suggests that sunlight and water, which are needed by living things, were available somewhere on Earth. So the ocean could not have been entirely covered with ice. The geologists say that sea ice would have been moving and forming patches of open water. These open patches would have provided good places for life to survive.

According to the fossil record, all of the major groups within the Domain Eukaryota (except perhaps animals) existed before the ice formed. Scientists have a hypothesis that the cooling climate during Snowball Earth may have allowed animals to evolve. In face, times of stress in environments are thought to prompt new species to evolve.

Scientists don't know exactly what caused the glaciers to form or what caused them to melt, but there is evidence that at about the same time lots of volcanic eruptions were happening. This could mean the cold “Snowball Earth” time was either formed by, or ended by, volcanic activity.

Last modified May 24, 2010 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, ranging from seismology, rocks and minerals, oceanography, and Earth system science to astronomy!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Sea Ice in the Arctic and Antarctic

Sea ice is frozen seawater. It can be several meters thick and it moves over time. Although the salts in the seawater do not freeze, pockets of concentrated salty water become trapped in the sea ice when...more

Plate Tectonics

The main force that shapes our planet’s surface over long amounts of time is the movement of Earth's outer layer by the process of plate tectonics. This picture shows how the rigid outer layer of the...more

What Is a Mineral?

Minerals are the building blocks of rocks. They are non-living, solid, and, like all matter, are made of atoms of elements. There are many different types of minerals and each type is made of particular...more

Sea Level

Measuring sea level, the height of the ocean surface, allows scientists to calculate whether sea level is changing over time and how much sea level rise is happening now because of global warming. But...more

The Cryosphere

Frozen water is found in many different places on Earth. Snow blankets the ground at mid and high latitudes during winter. Sea ice and icebergs float in the chilly waters of polar oceans. Ice shelves fringe...more

Glaciers and Ice Sheets

For a glacier to develop, the amount of snow that falls must be more than the amount of snow that melts each year. This means that glaciers are only found in places where a large amount of snow falls each...more

Triggers of Volcanic Eruptions in Oregon's Mount Hood Investigated

Scientists have learned that Mount Hood, Oregon's tallest mountain, has erupted in the past due to the mixing of two different types of magma. "The data will help give us a better road map to what a future...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA