MOTHER GLACIER: The Larsen ice shelf on the east coast of the Antarctic peninsula.
Image: Courtesy of Noel Gourmelen
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It took a mere 85 million years—the geologic blink of an eye—for animals to evolve and radiate out over much of the world’s land and oceans. Although fossil records and molecular biology have provided much information on the spread of animal life, scientists have not been able to figure out exactly what sparked this massive diversification. New research shows that nutrient-rich runoff from massive melting glaciers may have provided the extra energy needed to fuel this dramatic evolution.
In the 1990s several scientists found evidence that much of Earth’s surface was covered with glaciers 635 million to 750 million years ago. They called their hypothesis “Snowball Earth.” Since then, many other studies have confirmed that it once may have been possible to ski from pole to pole. As the glaciers advanced, they scraped off the top layer of rock and soil on land and then released minerals and nutrients into the ocean as they retreated.
The moment of glacial runoff coincided with the rapid evolution of animal life. Biogeochemists Timothy W. Lyons and Noah J. Planavsky of the University of California, Riverside, knew as much, but what they could not understand was whether the runoff contained enough nutrients to spur animal evolution and whether the appearance of animals in the fossil record at this time was merely a coincidence. If they could measure phosphorus, a key nutrient in biological systems known to support the growth of microbes and algae, Lyons and Planavsky could surmise the total nutrient concentration. The problem was finding a way to measure the phosphate concentrations of oceans nearly one billion years old.
Lyons and his colleagues realized they could use iron-rich deposits from ancient, low-oxygen oceans high in dissolved iron to estimate how much phosphorus was in the water. “These iron-rich deposits scavenge phosphates in a very predictable and well-understood way,” says Lyons, who published his and Planavsky’s research recently in Nature. (Scientific American is part of Nature Publishing Group.) This discovery enabled the researchers to calculate marine phosphate concentration based on the phosphates in the iron-rich deposits. As the team expected, phosphate levels spiked in seven different samples around the world as the glaciers melted.
“A big pulse of phosphate would have supported a lot of life in the ocean,” Lyons says. This phosphate buffet would have encouraged the abundance of oxygen-producing algae and other organisms and increased oxygen levels spurring the explosion of animal evolution.
“This study links Earth’s geochemical systems with the evolution of life,” says Gabriel Filippelli of Indiana and Purdue Universities, who was not involved with the study. It also shows how one big chill might have changed life on Earth forever.
This article was originally published with the title When Earth Was a Snowball.
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9 Comments
Add CommentI have understood that the end of 'snowball Earth' was precipitated by some major volcanic events. In that case, mightn't the volcanic conditions have contributed to the development of life forms?
Reply | Report Abuse | Link to thisAlso, I seem to recall reading that it has not been definitively established that oceans were entirely frozen over. If not, couldn't oceanic life have continued to prosper through the 'snowball Earth' period?
jtdwyer-your comment about volcanic events is true because without the release of certain gases there wouldn't have the big melt.
Reply | Report Abuse | Link to thisSorry about the missing been.
Reply | Report Abuse | Link to thisLovelock and Gaia are two words that spring to mind reading this.
Reply | Report Abuse | Link to thisEarth may have become a snowball because of oxygen. For example, phytoplankton are dropping in population now (see S.A. article "Phytoplankton Population Drops 40 Percent Since 1950".)
Reply | Report Abuse | Link to thisAs oxygen decreases, temperature rises as it is rising now. When oxygen increased, as when Earth was a snowball, sunlight was blocked by oxygen, which caused global cooling. The snowball melted when oxygen decreased in concentration again after the passing away of the bloom of phytoplankton.
The fact that oxygen blocks sunlight and cools the Earth is evident in absorption plots (see graphs in Wikipedia article Greenhouse Gas). Instead of CO2 we should be concerned about oxygen concentration in Earth's atmosphere.
"When Earth Was a Snowball" is an interesting article but it leaves to the reader to do too much math. The figures provided, measuring "the phosphate concentration of the oceans nearly one billion years old." The evolution and radiation of animals took "a mere 85 million years." "Earths surface was covered with glaciers 650 million to 750 million years ago." From this one is left to conclude the coincidence of the melting of the glaciers and the evolution of animal life. A straight statement of when the glaciers melted and when animal life evolved would have provided a clearer picture.
Reply | Report Abuse | Link to thisEARTHS MOON
Reply | Report Abuse | Link to thisOrbits Earth in relation to Earths meandering magnetic poles, the Earth changing ever so slowly, it’s exposure to both the Sun and Moon.
Recent dramatic annual Earth tipping has the planet moving round and about it’s north, south, magnetic Axis.
Sun exposure being the reason for Tropical displacement
Moon exposure been the reason for Ocean displacement
cbc.ca bruce voigt
Global Warming causing an explosion of life on the planet? How politically incorrect can you get? Did the authors not get the IPCC memo?
Reply | Report Abuse | Link to thisBut it is politically correct to confuse global warming taking the average temperature from below freezing to above freezing with global warming taking the temperature from mild to hot?
Reply | Report Abuse | Link to thisAmazing. I'd never have guessed that seeing the words 'global warming' bypasses the higher neural functions, and directly triggers a typing reflex.