” Before this change, atmospheric carbon dioxide stayed high, leading to a steady, greenhouse environment. Clay forms on land as a residue of chemical weathering, the primary long-term procedure through which carbon dioxide is eliminated from the environment. This occurs when climatic carbon integrates with water to form a weak acid, carbonic acid, which falls to the ground as rain and dissolves rocks, launching ions consisting of calcium ions that flow into the ocean. Eventually, the carbon is locked up in rocks on the ocean flooring. In contrast, carbon drawdown by plant photosynthesis is negated once the plants decay, and rarely affects carbon dioxide levels on timescales longer than a couple of hundred years.

Water collects on mosses. The very first land plants were believed to be non-vascular, like mosses. Credit: Katmai Preserve NPS Photo/Russ Taylor
The arrival of plants on land about 400 million years earlier may have altered the way the Earth naturally manages its own climate, according to a new research study led by scientists at UCL (University College London) and Yale.
The carbon cycle, the process through which carbon moves between rocks, oceans, living organisms and the atmosphere, acts as Earths natural thermostat, regulating its temperature over very long time durations.
In a new research study, released in the journal Nature, scientists took a look at samples from rocks spanning the last three billion years and discovered evidence of a dramatic modification in how this cycle operated about 400 million years back, when plants began to colonize land.

Specifically, the researchers kept in mind a modification in the chemistry of seawater tape-recorded in the rock that shows a significant shift in the global formation of clay– the “clay mineral factory”– from the oceans to the land.
Tasting of Ordovician (450 million-year-old) sediments by first author Boriana Kalderon-Asael. Credit: Ashleigh Hood
Given that clay forming in the ocean (reverse weathering) results in co2 being launched into the environment, while clay on land is a by-product of chemical weathering that gets rid of co2 from the air, this minimized the amount of carbon in the environment, leading to a cooler world and a seesawing environment, with rotating ice ages and warmer durations.
The researchers recommended the switch was caused by the spread of land plants keeping soils and clays on land, stopping carbon from being cleaned into the ocean, and by the development in marine life using silicon for their skeletons and cell walls, such as sponges, single-celled algae and radiolarians (a group of protozoa), resulting in a drop in silicon in the seawater required for clay formation.
Senior author Dr. Philip Pogge von Strandmann (UCL Earth Sciences) said: “Our study recommends that the carbon cycle run in a fundamentally different way for the majority of Earths history compared to the present day.
” The shift, which happened gradually between 400 to 500 million years ago, appears to be connected to 2 significant biological innovations at the time: the spread of plants on land and the development of marine organisms that extract silicon from water to produce their cells and skeletons walls.
” Before this change, atmospheric co2 remained high, resulting in a steady, greenhouse climate. Since then, our environment has actually bounced back and forth in between ice ages and warmer durations. This type of modification promotes advancement and throughout this duration the evolution of intricate life sped up, with land-based animals forming for the first time.
” A less carbon-rich environment is also more conscious change, permitting human beings to influence the environment more quickly through the burning of fossil fuels.”
Author Boriana Kalderon-Asael, a PhD student at Yale University, said: “By measuring lithium isotopes in rocks spanning most of Earths history, we intended to examine if anything had actually changed in the performance of the carbon cycle over a large time scale. We discovered that it had, and this change seems connected to the development of plant life on land and silicon-using animal life in the sea.”
In the research study, scientists determined lithium isotopes in 600 samples of rock drawn from lots of different places worldwide. Lithium has 2 naturally occurring steady isotopes– one with 3 protons and three neutrons, and one with 3 protons and four neutrons.
When clay forms slowly on land, it strongly prefers lithium-6, leaving surrounding water enriched with the other, heavier isotope, lithium-7. Evaluating their samples utilizing mass spectrometry, the researchers found an increase in the levels of lithium isotope-7 in seawater tape-recorded in the rock happening between 400 and 500 million years ago, recommending a major shift in Earths clay production coinciding with the spread of plants on land and introduction of silicon-using marine life.
Clay forms on land as a residue of chemical weathering, the main long-term procedure through which co2 is eliminated from the environment. This happens when climatic carbon integrates with water to form a weak acid, carbonic acid, which falls to the ground as rain and liquifies rocks, releasing ions including calcium ions that stream into the ocean. Eventually, the carbon is locked up in rocks on the ocean floor. In contrast, carbon drawdown by plant photosynthesis is negated once the plants decay, and hardly ever impacts co2 levels on timescales longer than a few a century.
When clay forms in the ocean, carbon remains in the water and is ultimately released into the air as part of the continual exchange of carbon that takes place when air meets water.
Reference: “A lithium-isotope perspective on the development of carbon and silicon cycles” by Boriana Kalderon-Asael, Joachim A. R. Katchinoff, Noah J. Planavsky, Ashleigh v. S. Hood, Mathieu Dellinger, Eric J. Bellefroid, David S. Jones, Axel Hofmann, Frantz Ossa Ossa, Francis A. Macdonald, Chunjiang Wang, Terry T. Isson, Jack G. Murphy, John A. Higgins, A. Joshua West, Malcolm W. Wallace, Dan Asael and Philip A. E. Pogge von Strandmann, 14 July 2021, Nature.DOI: 10.1038/ s41586-021-03612-1.
The research study received support from the European Research Council and NASA.