Snowball Earth Huronian (Wikipedia)
Have you ever heard of “Snowball Earth” events? New research from the University of Washington provides a more complete picture for how the last Snowball Earth ended, and suggests why it preceded a dramatic expansion of life on Earth, including the emergence of the first animals.
These Snowball Earth events have happened only a handful of times and do not occur on regular cycles. Each lasts for millions of years or tens of millions of years and is followed by dramatic warming, but the details of these transitions are poorly understood.
Snowball Earth is a geological hypothesis that proposes that the Earth’s surface became nearly entirely frozen with no liquid oceanic or surface water exposed to the atmosphere during one or more of Earth’s icehouse climates. This extreme glaciation is believed to have occurred multiple times throughout Earth’s history, most notably during the Cryogenian period.
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Evidence of glaciers has been found in tropical latitudes, suggesting that ice sheets extended to the equator. During a Snowball Earth event, the carbon cycle would have been disrupted, leading to the deposition of large amounts of carbonate-rich rocks. The orientation of Earth’s magnetic field can be preserved in rocks, providing clues about where they were formed. Analysis of paleomagnetic data suggests that some rocks were formed near the equator during periods of extreme glaciation.
The Snowball Earth hypothesis remains a subject of ongoing research, but it provides a fascinating glimpse into Earth’s extreme past. Understanding these events can help us better understand our planet’s climate system and its potential future.
“Cap carbonates contain information about key properties of Earth’s atmosphere and ocean, such as changing levels of carbon dioxide in the air, or the acidity of the ocean,” said lead author of the study Trent Thomas, a UW doctoral student in Earth and space sciences. “Our theory now shows how these properties changed during and after Snowball Earth.”
Cap carbonates are layered limestone or dolomite rocks that have a distinct chemical makeup and today are found in over 50 global locations, including Death Valley, Namibia, Siberia, Ireland and Australia. These rocks are thought to have formed as the Earth-encircling ice sheets melted, causing dramatic changes in atmospheric and ocean chemistry and depositing this unique type of sediment onto the ocean floor.
They are called “caps” because they are the caps above glacial deposits left after Snowball Earth, and “carbonates” because both limestone and dolomite are carbon-containing rocks. Understanding their formation helps explain the carbon cycle during periods of dramatic climate change. The new study, which models the environmental changes, also provides hints about the evolution of life on Earth and why more complex lifeforms followed the last Snowball Earth.
“Life on Earth was simple — in the form of microbes, algae or other tiny aquatic organisms — for over 2 billion years leading up to Snowball Earth,” said senior author David Catling, a UW professor of Earth and space sciences. “In fact, the billion years leading up to Snowball Earth are called the ‘boring billion’ because so little happened. Then two Snowball Earth events occurred. And soon after, animals appear in the fossil record.”
