Ferns were some of the first land plants to colonise the continents.
Credit: Dr Tom Gernon
Another piece of the story of how Earth came to be the way is today has been revealed by an international team of scientists led by led by Dr Christopher Spencer of Queen’s University, Kingston, Ontario, Canada, and including researchers at the University of Southampton, Hampshire, UK, the University of Cambridge, Cambridgeshire, UK and the University of Geosciences, Wuhan, China.
They have shown how the evolution of land plants changed Earth's environment, paving the way for the eventual evolution of dinosaurs, 200 million years later, followed by birds and mammals and the diversity of vertebrates we see today.
And of course, it is entirely at odds with the account in the Bible which Creationists have been fooled into thinking is the way it happened. Obviously, magic was not involved anywhere in the process
Lutetium has a small proportion of naturally occurring radioactive 176Lu which, with a half-life of 37.1 billion years, decays to the stable isotope of hafnium, 176Hf, so, by measuring the relative proportions of 176Lu and 176Hf, the age of the zircon crystal can be estimated. The amount of 18O reflects the amount of weathering the sediment had been exposed to, in other words, how long it remained on the surface before being washed into the sea and subducted, while the radioactive decay records the passage of time since the crystals were formed in magma.
Read more: Wikipedia - Lutetium–hafnium dating
The roots of land plants increase the breakdown of rocks and simultaneously bind the resulting mud to form deeper soils and to create alluvial flood plains which in turn produces slow-moving meandering rivers and extensive deltas leaving more of the eroded surface on land rather than being washed into the sea.
The team hypothesised that the relatively sudden evolution of land plants, on a geological time scale, would increase the degree of weathering because the mud stays on the surface for longer. By analysing thousands of magmatic zirconium Crystals, this is exactly what was found to have happened around 430 million years ago, coincidental with the evolution of land plants. Suddenly, by geological standards, the product of erosion of surface rocks was staying around for much longer, as plants transformed Earth's surface by their presence.
The news release from Southampton University, explains the significance of this finding:
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.The researchers give more technical information in the abstract to their paper, published in Nature Geoscience, sadly behind an expensive paywall:
The proliferation of plants completely transformed Earth’s biosphere – those parts of the planet’s surface where life thrives – paving the way for the advent of dinosaurs about 200 million years later.
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.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.
Dr Christopher Spencer, lead author. Assistant Professor
Queen’s University, Kingston, Ontario, Canada.
To test this idea, the team studied a database of over five thousand zircon crystals formed in magmas at subduction zones – essentially ‘time capsules’ that preserve vital information on the chemical conditions that prevailed on Earth when they crystallised.When these rocks crystallise, they trap in vestiges of their past history, 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.
It is amazing to think that the greening of the continents was felt in the deep Earth. Hopefully this previously unrecognised link between the Earth’s interior and surface environment stimulates further study.
Dr Christopher Spencer, lead author
Assistant Professor
Queen’s University in Kingston, Ontario, Canada.
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.
The researchers show that vegetation changed not only the surface of the Earth, but also the dynamics of melting in Earth’s mantle.
AbstractSomething which continues to worry Creationists is the way science keeps on finding this sort of information which not only shows the Earth is old, but that the different scientific theories such as the Theory of Evolution are continually being supported by different strands of science, in this case, geology. This, of course, is exactly what we expect if science is right and Christian mythology isn't.
The evolution of land plants during the Palaeozoic era transformed Earth’s biosphere. Because the Earth’s surface and interior are linked by tectonic processes, the linked evolution of the biosphere and sedimentary rocks should be recorded as a near-contemporary shift in the composition of the continental crust. To test this hypothesis, we assessed the isotopic signatures of zircon formed at subduction zones where marine sediments are transported into the mantle, thereby recording interactions between surface environments and the deep Earth. Using oxygen and lutetium–hafnium isotopes of magmatic zircon that respectively track surface weathering (time independent) and radiogenic decay (time dependent), we find a correlation in the composition of continental crust after 430 Myr ago, which is coeval with the onset of enhanced complexity and stability in sedimentary systems related to the evolution of vascular plants. The expansion of terrestrial vegetation brought channelled sand-bed and meandering rivers, muddy floodplains and thicker soils, lengthening the duration of weathering before final marine deposition. 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. The late Palaeozoic isotopic shift of zircon indicates that the greening of the continents was recorded in the deep Earth.
Spencer, Christopher J.; Davies, Neil S.; Gernon, Thomas M.; Wang, Xi; McMahon, William J.; Morrell, Taylor Rae I.; Hincks, Thea; Pufahl, Peir K.; Brasier, Alexander; Seraine, Marina; Lu, Gui-Mei
Composition of continental crust altered by the emergence of land plants
Nature Geoscience (2022); DOI: 10.1038/s41561-022-00995-2
© 2022 Springer Nature Ltd.
Reprinted under the terms of the Copyright, Designs and Patents Act 1988, s60.
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