February 1, 2012
Rise Of Land Plants Caused Planet’s Temperature To Plummet
Based on the results of a set of novel new experiments, scientists have theorized that the rise of terrestrial plants in Earth´s natural history may have initiated a series of ice ages that researchers have previously been at a loss to explain.
According to the theory, as plants began to take root across the planet´s land masses, they extracted minerals from rocks and absorbed free atmospheric carbon, ultimately precipitating a significant drop in global temperatures.
Professor Timothy Lenton at England´s University of Exeter led a team of researchers with a variety of backgrounds in concocting an experiment that attempted to recreate the conditions on Earth´s continents during the Ordovician period some 488-444 million years ago.
Mimicking the nascent age of terrestrial plants, Lenton´s crew covered rocks with moss similar to that which became prevalent during the Ordovician and then incubated them under controlled conditions.
Closely monitoring the growing moss over a period of three months, the team observed that as the plants grew and spread, they dissolved the rocks on which they were growing which, in turn, caused the release of a significant quantity of calcium and magnesium ions into the surrounding environment.
These charged atoms, explained the researchers, are known to bond with atmospheric carbon, capturing the greenhouse gas and converting it into a stable chemical compound. The new compound then washes into oceans where it forms carbonate rocks, permanently trapping the previously free-floating carbon.
The researchers say that this process offers key insights into how early plant life may have drastically altered Earth´s geochemistry and climate. Just this plant-induced trapping of carbon alone may have been enough to cause global temperatures to plummet by 9 degree Fahrenheit they say.
And this, say the researchers, would go a long way in helping to explain the enigmatic large-scale glaciations that geologists have observed took place during the Ordovician period.
Moreover, the researchers noted that these are just the geochemical effects of one of many activities that plants carry out.
Lenton´s study also pointed out that plants extract phosphorus and iron from rocks as well, both of which are subsequently released into the environment after the plants die. Many of these released nutrients would have washed out into the sea where they became critical for the growth of microscopic plankton.
And plankton, as every marine biologist knows, are critical for their role in capturing and sequestering free atmospheric carbon as they grow and reproduce. Once converted from its atmospheric form into biological compounds, the carbon remains in the water after the plankton die where it is incorporated into rock formations on the ocean floor.
Researchers believe that as much as 15 percent of the planet´s terrestrial surface was covered with these primitive forms of plant life. Yet Lenton says that even if one assumes a much more conservative estimate of 5 percent, the cooling effect on the atmosphere due to plant life would have still have been significant.
“This study demonstrates the powerful effects that plants have on our climate,” said Lenton.
Turning the results of his research to the modern day phenomenon of global warming, Lenton also evaluated the role of today´s plants in offsetting rising temperatures.
“Although plants are still cooling the Earth´s climate by reducing the atmospheric carbon levels, they cannot keep up with the speed of today´s human-induced climate change,” he explained.
“It would take millions of years for plants to remove current carbon emissions from the atmosphere.”
The results of the study are published in Nature Geoscience.
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