How soil imprisons ancient carbon

Blogging on Peer-Reviewed Research

Deep underground, there lies a sleeping giant that we would do well to avoid waking. The giant is a massive, dormant amount of carbon, and it’s better for us that it remains trapped in the ground rather than circulating in the atmosphere as carbon dioxide.

Soil changes characteristics with depthMany of the most crucial debates of the 21st century will involve reducing the amount of carbon dioxide being pumped into the atmosphere. The many possible solutions include trapping carbon, either in the trunks of trees or in underground vaults. The irony is that a massive amount of carbon is already locked safely away underground.

The world’s soil acts as a carbon prison and it holds more of it than the earth’s atmosphere and all of its living things combined. Over three trillion tonnes of the element are incarcerated in soil and about 80% of this is found at depths of up to 3 metres. At these levels, carbon is very stable and plays no part in the carbon cycle, the process where the element is exchanged between the land, air and sea.

Now, Sebastien Fontaine and other scientists from the French National Institute for Agricultural Research have found that deep soil retains carbon so well because it lacks enough fuel for the microbes that decompose organic matter.

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How India became the fastest continent

You don’t normally hear continents described as speedy, but it’s now clear that some are much faster than others. India, in particular, is the Ferrari of continents and now, scientists have discovered why.

When continents break up

Gondwana splitsRewind 150 million years and the Earth looked very different. Most of the land in today’s southern hemisphere were united in a single super-continent called Gondwana, including Africa, Australia, South America, Antarctica, India and Arabia.

The Earth’s crust is not a stationary shell but an ever-shifting mosaic of tectonic plates that constantly (albeit slowly) reshape the face of the planet. Underneath the crust lies the much hotter mantle, and plumes of super-heated rock occasionally erupt out of this layer, causing hotspots of volcanic activity.

Geologists believe that a particularly large ‘mantle plume’ kick-started the break-up of Gondwana. Now, Prakash Kumar and colleagues from the National Geophysical Research Institute in India have found that the plume also gave India a turbo boost.

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Did climate change kill off the Neanderthals? Not likely…

The reasons why the Neanderthals died off remain a mystery. One of the major theories says that they were the victims of major climate changes, but new evidence suggests that this is an unlikely scenario.

In an age where climate change driven by our own hand is poised to cause catastrophic changes to human life, it seems fitting to work out if shifting climates also doomed our evolutionary cousins, the Neanderthals.

A Neanderthal hunter - did he fail to compete with humans?The question of why the Neanderthals died out has been the source of fierce debate since the first bones were discovered in the early 19th century. Some scientists turned the finger of blame inwards, suggesting that early humans killed them off, either directly, through violence and the spread of new diseases, or indirectly by gradually out-competing them.

Others have accused changing climates. According to them, Neanderthals were adapted to cold environments and, being less flexible than humans, they were unable to cope with a warming post-Ice Age world.

Now, Chronis Tzedakis from the University of Leeds has found compelling evidence that the Neanderthals extinction was unlikely to have coincided with the extreme shifts in climate at the end of the last Ice Age.

While their findings don’t rule out the climate change model completely, they strongly suggest that it wasn’t a major factor in the Neanderthals’ downfall.

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Megaflood in English Channel separated Britain from France

At a time when severe flooding is still causing problems in the North of England, it’s worth noting that flooding was a key factor in Britain’s past. Hundreds of thousands of years ago, one of the largest floods in Earth’s history turned us into an island and changed the course of our history.

Britain was not always isolated from our continental neighbours. In the Pleistocene era, we were linked to France by a land ridge called the Weald-Artois anticline that extended from Dover, across what are now the Dover Straits.

This ridge of chalk separated the North Sea on one side from the English Channel on the other. For Britain to become an island, something had to have breached the ridge.

 

Britain was once connected to France by a land ridge.

Under the Channel

Now, Sanjeev Gupta and colleagues from Imperial College London have found firm evidence that a huge ‘megaflood’ was responsible. They analysed a hidden series of massive valleys on the floor of the English Channel – vast gouges of bedrock 50 metres deep and tens of kilometres wide.

These valleys were first noticed by geologists in the 1970s but until now, no one really knew what caused them. Gupta decided to find out with the help of some modern technology. He used high-resolution sonar to create a contour map of the Channel floor, and found that this hidden world was remarkably well preserved.

The megaflood sent a million cubic metres of water flowing into the Channel every second.He saw a clear picture of the huge, linear valleys, branching out in a westerly direction. In and among the valleys lay long ridges and grooves running parallel to the channel, V-shaped scours that taper upstream, and streamlined underwater islands up to 10km long.

All in all, these images show that the valleys are geological scars, formed by erosive torrents of water travelling west from the Dover straits. Their size and features are consistent with a massive flood, carving out the land in its wake.

Where did the water come from?

During the Pleistocene, the North Sea was actually a giant lake, closed off at its northern edge by merged ice sheets from Britain and Scandinavia, and at its southern edge by the Weald-Artois ridge.

This lake was fed by both the Thames and the Rhine rivers. That, combined with the melting ice, eventually burst the Weald-Artois barrier, sending the lake’s water surging into the Channel.

Gupta estimated that the flood would have lasted for several months and involved at least two episodes. At its peak, one million cubic metres of water flowed into the Channel every second, a thousand times more than the Victoria Falls.

The megaflood changed both the local geography and the course of British history. It reorganised the drainage of the Thames and Rhine rivers to the Channel rather than the North Sea. And most importantly, it permanently separated Britain from continental Europe.

A megafloor changed the drainage of the Thames and Seine into the Channel rather than the North SeaThe flood made migration into the newborn island more difficult and aside from some early attempts at settlement, Britain was completely devoid of humans for about 100,000 years.

Once humans finally colonised this green and pleasant land, our island status has affected our entire history from our power as a naval empire, to our strategies during the Second World War to our national character.

 

Reference: Gupta, Collier, Palmer-Felgate & Potter. 2007. Catastrophic flooding origin of shelf valley systems in the English Channel. Nature 448: 342-346.

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Top image from original Nature paper.