UKH

Making Mountains out of Marine Drifters: How Plankton Shaped Peaks Article

© Hamish Frost

Many of the mountain ranges we walk and climb up would be far less vertiginous were it not for the lubricating effects of plankton, a new study has revealed. Two billion years ago, a boom in the microscopic marine organisms led to prime conditions for orogeny, or mountain building. As the Earth's tectonic plates collided, the carbon from dead plankton on the sea bed became slick graphite under heat and pressure, which acted as a lubricant enabling the sliding, stacking and folding of the Earth's crust to form mountain ranges. Without it, friction would quickly have ground things to a halt, making molehills rather than the lofty peaks we know and love today.

Amongst the giants of the Garhwal Himalaya. Crossing the Kirti Bamak glacier below Meru and Shivling.  © Hamish Frost
Amongst the giants of the Garhwal Himalaya. Crossing the Kirti Bamak glacier below Meru and Shivling.
© Hamish Frost

Geology has long shaped life on Earth, but this study by Professor John Parnell of Aberdeen University and Dr Connor Brolly from the University of Glasgow is an example of the reverse: living matter actively influencing the geological lay of the land. While scientists have long understood that lubrication was involved in plate collisions and mountain building, the source of the slipperiness was unknown.

In the lead up to their discovery, Professor Parnell was researching the consequence of the abundance of carbon two billion years ago during a time known as the Palaeoproterozoic period, an era in which oxygen levels increased in the oceans and atmosphere, eventually leading to the formation of more complex life forms.

The study involved analysing existing data sets listing the carbon content in 20 orogens - regions of mountain-making disturbance - across the globe, from Australia to China, South America to the Arctic and in north-west Scotland. An analysis of the time interval between the burial of organic carbon and mountain-building indicated that high biomass and plate tectonics are linked.

Timeline for events in Earth history, including explosion of plankton followed by mountain formation, c. 2 billion years ago.  © J. Johnston
Timeline for events in Earth history, including explosion of plankton followed by mountain formation, c. 2 billion years ago.
© J. Johnston

"The importance of carbon-rich rocks to mountain building started two billion years ago, when plankton were extremely abundant and their remains formed carbon-rich rocks on the sea floor," Parnell says. "The abundance of carbon was a result of plentiful nutrients after glaciation eroded the land surface, and cells became bigger, resulting in more carbon."

Extra carbon not only lubricated rock sheets, but made them more susceptible to deformation and, as a consequence, easier to stack and fold on a large scale. Imagine building a tower of pancakes by layering one on top of the other, using black crême fraiche to simulate graphite for lubrication.

photo
Using black crême fraîche to simulate graphite for lubrication between the pancakes acting as rock slabs.
© W. Ritchie

The study demonstrates 'the integral relationship' between the biosphere [the places on Earth where life exists] and the lithosphere [the Earth's outer layer],' the paper's synopsis explains. While the biosphere has less of an impact on the lithosphere, rather than vice-versa, this study and others have shown that it can be a two-way process.

"Even before two billion years ago, phytoplankton (life) was oxygenating the atmosphere by photosynthesis and fundamentally changed the chemistry of the surface environment, including weathering," Parnell says.

Earth's topography two billion years ago was vastly different and more dramatic compared to today's ranges and massifs. There were a greater number of large mountain ranges due to different tectonic plate configurations, Parnell explains, which have subsequently eroded. These ancient mountains were also bare of any vegetation, since land plants had not yet evolved. 

The highest mountain range in the world today, the Himalaya, earned its height through being one of the largest orogenic belts in the world, coupled with its relatively young age - about 50 million years - meaning that little erosion has occurred, Parnell explains. Two major slides - one occurring in the first few millions of years after the rocks were first formed, the other after a long dormancy period - contributed to the geology of the 8,000-metre giants. It's possible that the range may slide again in the distant future.

Simplified figure to show slabs of rock stacked by lubricating carbon to make mountains when tectonic plates collide.   © J. Bowie
Simplified figure to show slabs of rock stacked by lubricating carbon to make mountains when tectonic plates collide.
© J. Bowie

Closer to home, Parnell studied the Lewisian complex, where evidence of mountain-building is visible today. North-West Scotland and the Outer Hebrides are interesting areas geologically, as well as popular destinations for climbers. The Lewisian rocks have been through several mountain building episodes, he explains.

"The mountains we see on the mainland are mostly a product of the Caledonian orogeny, which occurred about 450 million years ago," Parnell says. "The slip surfaces that allowed stacking of rock slices then occurred in mixed graphitic shales, gypsum and limestones. However, we can still see the stumps of the much older Palaeoproterozoic orogeny in the rocks of the Outer Hebrides, Tiree/Coll, Glenelg and Gairloch." The slippery graphitic rocks from two billion years ago that enabled the process are exposed by the roadside near the Gairloch Hotel (opposite the viewpoint carpark), and at Rodel Church in Harris.

In addition to lubricating mountain formation, Parnell discovered, the carbon had chemical effects on the Earth's crust, which caused valuable metal ores to precipitate, including nickel, vanadium and uranium — all of which will be vital in a green economy. Graphite and other ores locked in the geological cycle are now used in green energy technology to create fuel cells and lithium ion batteries, playing a role in potentially preserving our planet.

"The carbon in the Earth's crust, derived largely from life, has caused the planet to evolve in a particular way," Parnell says. "If that carbon had been lacking, the planet would have evolved in a different way. It's our challenge to use the planet we've got in the most sensible way going forward." 

In a warming world, rising temperatures are not expected to impact the rate of orogeny, which has remained fairly consistent since the Palaeoproterozoic plate convergence two billion years ago. 

"The rate should continue more or less the same," Parnell says. "The critical biomass of phytoplankton is not predicted to decline, and might rise with warming of sea water."

Yet as permafrost in the high mountains melts due to global warming and rockfall increases, humans are effectively contributing to the 'demolition' of mountains.

"Ours is a planet fundamentally shaped by life," Parnell concludes. 



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2 Feb

Plankton lubricating orogenous zones? Ooooo matron!

I was going to make that joke in the piece...but it seemed to undermine the serious science!

Chapeau!

I think the word orogenous doesn't exist...but orogenic does. Probably for that reason!

3 Feb

Black creme fraiche?

3 Feb

Does this mean mountains aren't, err.... vegan?

Yeah why not use blackcurrant jam?!

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