A new study conducted by UCL (University College London) and researchers from Yale shows that the arrival of plants on Earth about 400 million years ago changed the way the Earth naturally regulates its climate.
The carbon cycle is the process by which carbon moves between rocks, oceans, living things and the atmosphere, acting as the Earth’s natural thermostat that regulates its temperature for a long time.
In a study published in a new journal the natureIn the study, scientists looked at rock samples from the past three billion years and found evidence of dramatic changes in the way this cycle functioned about 400 million years ago, when plants began colonizing the Earth.
Researchers have particularly noticed changes in the chemistry of seawater recorded in the rock, which indicates a significant change in the composition of global mud – “mud factories” – from the ocean to the land.
Because ocean dirt (reverse weather) releases carbon dioxide into the atmosphere, and land-based dirt is a byproduct of chemical weather removal that removes carbon dioxide from the air, reduces the amount of carbon in the atmosphere caused by the planet and climate change, glacier changes and warmer periods. .
The researchers said the transition was caused by the multiplication of terrestrial plants that support land and dirt on land, stopping carbon from drifting into the ocean, and the growth of marine life using silicon, like sponges, for grains and cell walls, came out separately. cellular and radioactive algae (a group of protozoa) that reduce the amount of silicon needed to form mud in seawater.
Senior author dr. Philipp Pugh von Strandmann (UCL Earth Sciences) said: “Our study shows that the carbon cycle works very differently in almost the entire history of the Earth than it does today.
“The transformation between 400 and 500 million years ago seems to be linked to two major biological innovations of the time: the spread of plants on land and the growth of cellular organisms that extract silicon from water to create their own skeletons.
Prior to this change, atmospheric carbon dioxide remained elevated and stabilized global warming. Since then, between the ice age and the warmer period, our climate has bounced back and forth. Changes of this type encourage evolution and during this period the development of complex life was accelerated for the first time by the formation of terrestrial animals.
“The low-carbon atmosphere is also more sensitive to change, which makes it easier for people to influence the climate by burning fossil fuels.”
The first author, Boriana Calderon Asil, a doctoral student at Yale University, said: “By measuring lithium isotopes in rocks that cover most of Earth’s history, we have tried to investigate whether anything has changed the functioning of the carbon cycle over time. that this was the case and that this change seems to be related to the growth of plants and terrestrial animals that use silicon at sea. “
In the study, the researchers measured lithium isotopes from 600 rock samples taken from many different locations around the world. Lithium in nature has two naturally stable isotopes – one with three protons and three neutrons, the other with three protons and four neutrons.
When clay is slowly formed in the soil, it largely supports lithium-6, so the surrounding water is rich in a heavier isotope, lithium-7. Analyzing their samples by mass spectrometry, the researchers found elevated levels of lithium-7 in seawater trapped in the rocks. this happened 400 and 500 million years ago, indicating a significant change in the production of clay on Earth that coincides with the spread of plants on Earth. The emergence of land and marine life using silicon.
On Earth, mud forms as a chemical remnant of the atmosphere, the main long-term process that removes carbon dioxide from the atmosphere. This happens when carbon in the atmosphere combines with water to form a weak acid, carbonic acid that falls to earth during rain and dissolves rocks, releasing ions, including calcium ions, that flow into the ocean. After all, coal is trapped in the rocks at the bottom of the ocean. In contrast, plant photosynthesis eliminates the removal of carbon when plants decay, and this rarely affects carbon dioxide levels over a period of more than a few hundred years.
When an impurity forms in water, carbon remains in the water and is eventually released into the air as part of the liquid carbon exchange that takes place when air enters the water.
Reference: “Perspective of lithium isotope evolution of carbon and silicon cycles”, Boriana Calderon-Asil, Joachim AR Kacchinov, Noah J. Blanavski, Ashley v. S. Hood, Matthew Dillinger, Eric J. Belfreud, David S. Jones, Akel Hoffmann, U.S. Frantz, Frances A. McDonald, Zhongiang Wang, Terry T. Eason, Jack J. Murphy, John A. Higgins, A. Joshua West, Malcolm W. Vallace, Dan Asel and Philip AE Pugh von Strandmann, 2021. 14 July the nature.
DOI: 10.1038 / s41586-021-03612-1
The study was supported by the European Research Council and NASA.