SoylentNews

hubie [soylentnews.org] writes:

Scientists at the University of Southampton have discovered that the evolution of land plants caused a sudden shift in the composition of Earth's continents [southampton.ac.uk]:

The evolution of land plants took place about 430 million years ago during the Silurian Period, when North America and Europe were conjoined in a landmass called Pangaea.

[...] "Plants caused fundamental changes to river systems, bringing about more meandering rivers and muddy floodplains, as well as thicker soils," says Dr Christopher Spencer, Assistant Professor at Queen's University in Kingston, Ontario, lead author of the study. "This shift was tied to the development of plant rooting systems that helped produce colossal amounts of mud (by breaking down rocks) and stabilised river channels, which locked up this mud for long periods."

The team recognised that Earth's surface and deep interior are linked by plate tectonics – rivers flush mud into the oceans, and this mud then gets dragged into the Earth's molten interior (or mantle) at subduction zones where it gets melted to form new rocks.

"When these rocks crystallise, they trap in vestiges of their past history," says Dr Tom Gernon, Associate Professor of Earth Science at the University of Southampton and co-author of the study. "So, we hypothesised that the evolution of plants should dramatically slow down the delivery of mud to the oceans, and that this feature should be preserved in the rock record – it's that simple."

[...] The team uncovered compelling evidence for a dramatic shift in the composition of rocks making up Earth's continents, which coincides almost precisely with the onset of land plants.

Notably, the scientists also found that the chemical characteristics of zircon crystals generated at this time indicate a significant slowing down of sediment transfer to the oceans, just as they had hypothesised.

[...] "It is amazing to think that the greening of the continents was felt in the deep Earth," concludes Dr Spencer.

Journal Reference:
Spencer, C.J., Davies, N.S., Gernon, T.M. et al. Composition of continental crust altered by the emergence of land plants. Nat. Geosci. (2022). 10.1038/s41561-022-00995-2 [doi.org]

Original Submission