- Scientists have found a link between ocean nutrient levels and tectonic activity over the past 700 million years and may have driven evolution
- Tectonic plates crashing into each other forced up mountain ranges
- This led to increased levels of erosion and so nutrients in the sea rose
- When erosion decreased, nutrients fell and may have caused extinctions
The notion of continents drifting on molten rock was unimaginable to Charles Darwin when he published his theory of evolution by natural selection in 1859. But researchers claim to have found evidence that the regular collision of tectonic plates over the past 700 million years has been a prime driver of evolutionary change on Earth. By tracking how nutrients in the oceans changed at key times in Earth’s history, the study found a correlation between mountain formations, a drop in nutrient levels and evolutionary changes. They claim there were certain periods in Earth’s history when nutrients appear to have been highly enriched in the oceans. While there were other periods when these nutrients were critically low.
These periods appear to correlate with times when the diversity of life on Earth exploded or contracted and it may have been a period of extreme low nutrients that led to animals moving on to the land. Writing for the Conversation, Professor Ross Large, a geologist at the University of Tasmania, and Professor John Long, a palaeontologist at Flinders University in Adelaide, South Australia, said the changes in nutrients may ultimately have a link to the movement of the tectonic plates. They said: ‘Nutrients in the oceans ultimately come from weathering and erosion of rocks on the continents. ‘Weathering breaks down the minerals in the rocks and releases the nutrient trace elements, which nourish life. ‘Thus when weathering and erosion rates increase for extended periods, more nutrients are supplied to the oceans. ‘In the long term of geological history, erosion rates rise dramatically during mountain building events caused by the gradual collision of tectonic plates. ‘Continued erosion eventually depletes the surface of nutrients, causing a drop in the ocean’s nutrients. ‘This might have lead to extinction events in the seas.’
The researchers, whose most recent findings are published in the journal Gondwana Research, used laser technology to analyse more than 4,000 pyrite grains from mudstone samples obtained from the seafloor around the globe. They used this to determine how the concentration of trace elements – including copper, zinc, phosphorus, cobalt and selenium – in the oceans have varied over the past 700 million years.
They found, for example, there was a rapid rise in trace elements of nutrients in the oceans around 635 million years ago preceding the Ediacaran, when multicellular life exploded and again 541 million years ago before the Cambrian, when animal life took off. The researchers also found when nutrients in the ocean were critically low there would have been a depletion of plankton. This, they said, could have caused a slow down in the rate of diversification and may even have played a role in three major mass extinction events at the end of the Ordovician, Devonian and Triassic periods. They then compared these to geological records of the movements of the tectonic plates recorded by the formation of mountains around the world. The authors said: ‘While the link between these nutrient cycles as drivers of evolution and factors in mass extinction events remains to be proven, it really makes us think about evolution in a broad sense.
‘Plate tectonics and evolution both operate on the same time scale of millions of years, and it seems logical that they could be causally related. ‘The relationship between increased nutrients in the oceans with bursts of evolutionary change are clearly correlated for the early part of the cycles, but less clear is the correlation with the evolution of advanced land animals. ‘The researchers added that the origin of the first land animals about 370 million years ago corresponds with a decrease in oceanic nutrients and a series of mass extinction events in the oceans. They say it might explain why some marine animals began to leave the sea and evolved to live on land. However, they continued there is no corresponding change in nutrient levels to mark the appearance of the dinosaurs and mammals around 225 million years ago. ‘Perhaps the cycles pertain mainly to biodiversity in the oceans. ‘There is certainly a close correlation with the drop in nutrients and some global oceanic mass extinctions. ‘These events are being tested and explored further in further research on selenium, to be released soon.’