Thursday, December 2, 2021

Study reveals how explosion in ocean life built the first mountains

Precambrian geology and the Gairloch map
Part of The Shear Zone channel.
The Gairloch geological map, first published in 1893, covers a classic and diverse region of Precambrian geology in NW Scotland.
We can use this to investigate the evolution of continental crust in the area - story that begins over three billion years ago with the development of the Part of The Shear Zone channel.
We can use this to investigate the evolution of continental crust in the area - story that begins over three billion years ago with the development of the Lewisian rocks and culminates, for us, in the blanketing of the region by the one billion year old Torridon Group sandstones.
There are some great outcrops....
From Forbes by David Bressan
An unprecedented abundance of oceanic life played a crucial role in the creation of Earth's first big mountains, a study led by scientists at the University of Aberdeen and published in the journal Communications Earth and Environment has revealed.
"Mountains are an essential part of the landscape, but big mountain chains only formed half-way through Earth's history, about two billion years ago," explains author Professor John Parnell from the University's School of Geosciences.
While the formation of mountains is usually associated with the collision of tectonic plates causing huge slabs of rock to be thrust skywards, the study has shown that this was triggered by an abundance of nutrients in the oceans two billion years ago which caused an explosion in microscopic life.

The motion of tectonic plates likely began about 3.5 billion years ago, driven by mantle plumes pushing aside parts of the Earth's crust.
But geological evidence in the form of Greenstone belts suggests that only low-lying mountains formed in the first one and a half billion years.
To allow the tectonic plates to move and solid masses of rocks to slide over each other, forming higher mountain ranges, a lubricating material is needed. Graphite, a carbon mineral, can act as such a material.
Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties. Life on Earth appeared at the same time plate tectonics started and is primarily carbon-based.

When the microorganism populating Earth's early oceans died, they fell to the ocean floor, they carbon-rich remains eventually forming graphite which played a crucial role in lubricating the breakage of rocks into slabs, enabling them to stack on top of each other to make high mountains.
The study has revealed that the amount of planktonic life was unusually high about two billion years ago, thus creating the necessary conditions that were crucial to the emergence of mountains over millions of years.
In Scotland, fragments of a supercontinent that existed at the end of the early Proterozoic period (2.5 to 0.5 billion years ago) are exposed on the surface by erosion.
Minerals formed under high-pressure conditions, like experienced during mountain building processes, found here suggest that these basement rocks were once the roots of an ancient mountain range.

"The geological record for this period includes evidence of an abundance of organic matter in the oceans, which when they died were preserved as graphite in shale. While it has long been known that tectonic processes were lubricated, our research shows that it was the sheer abundance of carbon in the ocean that played a crucial role in the crustal thickening that built the Earth's mountain ranges. We can see the evidence in the northwest of Scotland, where the roots of the ancient mountains and the slippery graphite that helped build them can still be found, in places like Harris, Tiree and Gairloch," Professor Parnell summarizes the study's results.

"Ultimately what our research has shown is that the key to the formation of mountains was life, demonstrating that the Earth and its biosphere are intimately linked in ways not previously understood."
Study co-author Dr. Connor Brolly, from the University of Glasgow, said: "Graphite buried in Earth's crust is in high demand for future green technology, for use in items such as fuel cells and lithium-ion batteries.
It's interesting to think that this two-billion-year-old event which was responsible for shaping our natural world now has the potential to play a key role in its preservation for future generations."
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