Arrival of land plants changed Earth’s climate control system

The arrival of plants on land about 400 million years ago may have changed the way the Earth naturally regulates its own climate, according to a new study led by researchers at UCL and Yale. The carbon cycle, the process through which carbon moves between rocks, oceans, living organisms and the atmosphere, acts as Earth's natural thermostat, regulating its temperature over long time periods. In a new study researchers looked at samples from rocks spanning the last three billion years and found evidence of a dramatic change in how this cycle functioned about 400 million years ago, when plants started to colonise land. Specifically, the researchers noted a change in the chemistry of seawater recorded in the rock that indicates a major shift in the global formation of clay - the "clay mineral factory" - from the oceans to the land. Since clay forming in the ocean (reverse weathering) leads to carbon dioxide being released into the atmosphere, while clay on land is a byproduct of chemical weathering that removes carbon dioxide from the air, this reduced the amount of carbon in the atmosphere, leading to a cooler planet and a seesawing climate, with alternating ice ages and warmer periods. The researchers suggested the switch was caused by the spread of land plants keeping soils and clays on land, stopping carbon from being washed into the ocean, and by the growth in marine life using silicon for their skeletons and cell walls, such as sponges, single-celled algae and radiolarians (a group of protozoa), leading to a drop in silicon in the seawater required for clay formation.