This page was the result of a project for a Global Climate Change course at Miami University.
What is the theory of snowball Earth?
**Listen to a radio broadcast by National Public Radio about this topic: www.npr.org/ramfiles/980827.atc.04.ram
The theory of snowball Earth states that the continents and oceans were covered in ice approximately 600 million years ago. The Earth may have remained in this frozen form, but it was rescued by the release of volcanic gases. While the Earth was in a deep freeze, chemical cycles were halted; as a result, carbon dioxide accumulated in the atmosphere causing an extreme greenhouse effect. After 10 million years of deep freeze, the Earth thawed in only a few hundred years. These dramatic events may have caused the explosion of life forms seen in Cambrian fossils (Hoffman and Schrag 2000).
Brian Harland first proposed the idea of a Precambrian great glaciation in 1964 after studying widespread glacial deposits. Later, in the late 1980ís, Kirschvink coined the term Snowball Earth (Hoffman and Schrag 1999). Since then, several people have contributed to the discussion of the possibility of Snowball Earth (Hoffman et al 1998, Hoffman and Schrag 2000).
**See diagrammatic explanation of Snowball Earth Theory
**See a complete Geologic Time Scale
What do you plan to accomplish?
We plan to compile data supporting this theory such as Isotope data (18Oxygen, 12/13Carbon, 86/87Strontium, 34Sulfur) from the Proterozoic period, fossil evidence from the Archaen to the Cambrian period, and unusual deposit data with estimated time periods (520-690 MA). Data will be entered into a timetable and comparisons will be made between these datasets to identify irregularities in years ranging from 520-690 MA. We will then attempt to explain what these irregularities mean in context of the occurrence of snowball earth.
Is there a correlation between the existing isotope data and unusual deposits during the Neoproterozoic (530-630 Ma) ?
Why is this research interesting and how does it relate to a larger question?
Snowball Earth may have been the catastrophic event that triggered the explosion of multicellular organisms (Hoffman and Schrag 2000). Single celled microorganisms had been present on the Earth since the Archaen, but the great diversity of life did not occur until after the global glaciation. The beginning of the Cambrian period marks when plants and animals began to appear in the fossil record. If the Earth had remained frozen, life as we know it today would not exist. These events that occurred during the late Proterozoic indicate a period of dramatic climatic change preceding a transitional time for the evolution of multicellular life.
Snowball Earth is also an interesting theory when we consider the changes in climate over time. This time period provides examples of two extreme climatic events - global warming and global glaciation. As we uncover information as to how organisms survived such extreme events, it may help us understand how life will continue through future global climate changes. Looking at past events can help us understand present and future climatic conditions.
What evidence do they have that snowball Earth existed?
Conditions on Earth were different during the late Proterozoic than they are today. Continents at the time of the Precambrian were located near the equator. (See movement of the continents at http://www.ucmp.berkeley.edu/geology/anim8.html) This is significant when we find evidence of glacial deposits on many of the continents. If the continents were glaciated at the equator, then the entire Earth must have been covered in ice.
The Sun was also weaker during the Precambrian, which may have helped advance the glaciers. Once the continents were glaciated to 30 degrees latitude, there was a runaway albedo effect. (Albedo refers to the reflective ability of a material. You can see the difference in how each material reflects sunlight in the following table.)
Source: Avery and Berlin 1992
As the Earth became covered in snow and ice, the albedo effect caused global glaciation. The interesting question, though, is how do they know these events occurred? Researches have been collecting evidence about past climatic events. However, in this evidence, anomalies have been found to have occurred during the late Proterozoic. When the relationships between the evidence was compared, the resulting explanation is the snowball Earth theory.