The experts report that when plants moved from water to land about 400 million years ago, the carbon cycle was drastically altered.
The carbon cycle – the transfer of carbon between rocks, oceans, living organisms, and the atmosphere – regulates Earth’s temperature over long periods of time.
The experts analyzed samples from rocks spanning the last three billion years and found evidence of a dramatic change in how the carbon cycle functioned when plants started to colonize land.
Recorded in the rocks, the researchers discovered a change in the chemistry of seawater that indicates a major shift in the global formation of clay from the oceans to the land.
The study suggests that the spread of terrestrial plants kept soils and clays on land, which stopped the flow of carbon into the ocean. In addition, an increase in the number of sponges and single-celled algae using silicon for their skeletons reduced the amount that was available for clay formation.
“Our study suggests that the carbon cycle operated in a fundamentally different way for most of Earth’s history compared to the present day,” said study senior author Dr. Philip Pogge von Strandmann.
“The shift, which occurred gradually between 400 to 500 million years ago, appears to be linked to two major biological innovations at the time: the spread of plants on land and the growth of marine organisms that extract silicon from water to create their skeletons and cells walls.”
“Before this change, atmospheric carbon dioxide remained high, leading to a stable, greenhouse climate. Since then, our climate has bounced back and forth between ice ages and warmer periods. This kind of change promotes evolution and during this period the evolution of complex life accelerated, with land-based animals forming for the first time.”
Dr. von Strandmann explained that a less carbon-rich atmosphere is also more sensitive to change, allowing humans to influence the climate more easily through the burning of fossil fuels.
“By measuring lithium isotopes in rocks spanning most of Earth’s history, we aimed to investigate if anything had changed in the functioning of the carbon cycle over a large time scale,” said study first author Boriana Kalderon-Asael.
“We found that it had, and this change appears to be linked to the growth of plant life on land and silicon-using animal life in the sea.”
The study is published in the journal Nature.