Plant evolution drastically changed Earth's composition

The evolution of land plants has radically changed the Earth’s chemical composition since their development 430 million years ago. This is the conclusion of an international team of scientists led by the University of Southampton.

Study lead author Dr. Christopher Spencer explained the effect land plants had on the Earth:

“Plants caused fundamental changes to river systems, bringing about more meandering rivers and muddy floodplains, as well as thicker soils. 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 researchers considered the conversion of soil to rock. They explain that mud travels from rivers, to oceans, to the Earth’s molten interior and eventually gets melted to become new rock.

“When these rocks crystallize, they trap in vestiges of their past history. So, we hypothesized 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,” explained study co-author Dr. Tom Gernon.

To carry out the study, the researchers analyzed thousands of zircon crystals which contained information about the chemical composition of the Earth at the time they were formed.

Through this analysis, the experts determined that rock composition drastically changed at almost the same time as the origin of land plants. At the same time, it seemed as though sediment was being transferred to the ocean at a slower rate than previously observed. Both of these findings support their hypothesis.

“It is amazing to think that the greening of the continents was felt in the deep Earth. Hopefully this previously unrecognized link between the Earth’s interior and surface environment stimulates further study,” said Dr. Spencer.

“Collectively, our results suggest that the evolution of vascular plants coupled the degree of weathering and timescales of sediment routing to depositional basins where they were subsequently subducted and melted,” wrote the researchers. “The late Palaeozoic isotopic shift of zircon indicates that the greening of the continents was recorded in the deep Earth.”

The study is published in the journal Nature Geoscience.

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By Erin Moody , Earth.com Staff Writer