Geologically speaking, land plants are a relatively recent development, having existed for just under 500 million years – around 10% of Earth’s existence. Despite this, their emergence played a crucial role in shaping Earth as we know it today. While some of the outcomes of plant emergence are obvious – such as paving the way for other life forms on land – the impact on Earth’s geology, while significant, is less apparent.
A global team, led by Christopher J Spencer at Queen’s University, Ontario, Canada, investigates the effect of land plants on the composition of Earth’s crust by compiling and statistically analysing zircon isotopic data taken from 183 publications. The zircons formed as new continental crust above subduction zones, where sediments derived from the land and delivered to the oceans via rivers are recycled. The team identifies a significant change in the composition of the continental crust around 430 million years ago, which coincides with the evolution of more complex vascular land plants. They propose that sediments were affected by an increase in biological weathering, with geochemical and fossil evidence suggesting that the main source of clay production shifted from the oceans to land at around the same time that land plants were spreading. The disruption of sediment transport to the oceans due to plants holding materials in place, exposing them to further weathering, is also likely to have played a role.
Other potential explanations for the observed correlation, such as significant tectonic or climatic events, are considered but deemed less likely. The study implies that the emergence of land plants had an impact on both sedimentary and igneous rocks, highlighting the connected evolution of the biosphere and the rock cycle.
Stephen McHugh
DETAILS Nat. Geosci., 15, 735-740 (2022); doi.org/10.1038/s41561-022-00995-2
