Researchers have known for years that carbon is stored in the earth’s mantle, a layer of plastic-like rock that lies beneath the planet’s fragile crust.
However, the amount of carbon is unknown. Most estimates, drawn from analyses of gases emerging from the mantle, say the store is many times more than all the carbon in the earth’s atmosphere, soil and sea combined.
Scientists are concerned that if just part of this gigantic reservoir is quickly released as carbon dioxide (CO2) it could create a runaway greenhouse effect. The CO2-soaked atmosphere would store up heat from the sun, shrivelling plant life and destroying species along the food chain.
German scientists conducted an experiment aimed at finding whether mantle rock is a stable storage for carbon dioxide. Most of the rock in the earth’s upper mantle is a crystalline silicate called olivine.
In a laboratory chamber, German scientist Hans Keppler’s team replicated the fiery heat and intense pressures of 1,200 Celsius and 3.5 Gigapascals, which are likely to exist in the deeper parts of the upper mantle.
They used these conditions to create olivine crystals from raw ingredients of magnesium oxide and silicon dioxide and expose them to carbon and water.
The carbon turned out to be almost completely insoluble in olivine-just a tiny amount was absorbed into the rock.
If the carbon is not in the olivine, that leaves only one major source which are carbonates, said Keppler.
Carbonate rocks have a much lower melting point than olivine, which is able to absorb the punishing furnace-like heat radiating from the earth’s core and still not melt.
Could humans meet a similar end
to the dinosaurs?
Heated to a molten state, carbonates are capable of squeezing through cracks in the olivine, rising up towards the surface and absorbing the free carbon as they go.
They can pick up so much that as much as 10 or 20 percent of their mass is carbon.
The risk, says Keppler, is that this carbonate reservoir could suddenly be breached in the event of a major volcanic eruption.
The nightmare is of a gigantic spewing of CO2, imperilling life on planet earth.
Evidence indicates that something similar to this scenario has taken place in the past.
“There is a very good correlation with (CO2) flooding that coincides with several mass extinction events-some massive, sudden change of carbon dioxide in the atmosphere,” said Keppler.
One of these events took place around 245 million years ago, during the largest extinction in the earth’s history. Fossil evidence shows as many as 96 percent of all marine species were lost and more than three quarters of vertebrate species on land.
Another event, or possibly a series of smaller events, was around 208 million years ago when half of the world’s species suddenly died out.
That event essentially handed rule of the planet to dinosaurs. Their domination ended, some 65 million years ago, by a mass extinction apparently caused by an asteroid impact, kicking up dust that triggered climate change.