Technology Going underground
A project to reveal more about all the carbon on Earth
THE carbon cycle is the stuff of school books.
It is a familiar tale of photosynthesis, forests, farming and fossils fuels.
Understanding this cycle is important, both because it sustains life on Earth and because it is bound up with the rate of global warming.
But are the outlines of the carbon cycle really that familiar?
At the AAAS meeting in Washington, DC, Robert Hazen of the Carnegie Institution for Science, which is based in the same town, gave a lecture intended to show that this view of the carbon cycle only scratches the surface.
Dr Hazen is one of the moving spirits behind a project called the Deep Carbon Observatory, which will be paid for by the Alfred P. Sloan Foundation.
Hazen博士是一个叫做地底碳观察项目的策划人，这个项目即将得到Alfred P. Sloan基金会的资助。
Over the course of the next decade it will attempt to understand all the carbon in the Earth, not just the stuff that cycles through the atmosphere, the oceans and living things.
As Dr Hazen pointed out, carbon is the fourth-most-abundant element in the universe, after hydrogen, helium and oxygen.
In the Earth, though less common than that, it is reckoned to make up between 0.07% and 3.2% of the planet.
But the uncertainty of this range is itself a comment on how little carbon's role in the Earth's overall physics and chemistry is understood.
Also uncertain is how much interchange there is between the carbon in the Earth's mantle and core, and the more familiar stuff in the crust, atmosphere and oceans.
Some carbon comes from the mantle to the surface in the form of diamonds.
These crystals, which can form only under the intense pressure of the Earth's deep interior, must have been erupted at unbelievable speed (about 100kph) to have survived the journey to the surface intact.
At slower speeds they would have turned into graphite, much to the chagrin of brides-to-be everywhere.
How, exactly, diamond forms is an important question. Diamonds are useful as an industrial material as well as gem stones, and they would have many more applications if they could be made cheaply. And another, even more important industrial material, petroleum, may also come from the mantle.
Among petroleum geologists in Western countries, the consensus is that crude oil and natural gas are formed near the Earth's surface from the fossilised bodies of living organisms.
Many Russians, though, disagree. They support the 130-year-old idea of their countryman Dmitri Mendeleev (who created the first version of the periodic table of elements).
He thought the temperatures and pressures of the mantle would convert carbonates and water into hydrocarbons.
That has, indeed, been done experimentally in the past.
And one role of the Deep Carbon Observatory will be to try to do it again in more sophisticated ways.
If it turns out that fossil fuels are abiogenic, that probably means they are more abundant than Western geologists think, and may be found in places hitherto thought unpromising.
Abiogenic petroleum could also provide food for one of the most intriguing targets of all for the Deep Carbon Observatory: the bacteria that live in the Earth's depths.
Current estimates suggest that half of all the living matter on Earth lives underground, at depths of up to 5km.
Some people think the share may be bigger than that. Indeed, there is loose talk of life having originated more than once in the distant past, and of there being entire shadow biospheres of organisms completely unrelated to anything on the surface.
Intriguingly, a few diamonds bear signs that their carbon was once part of living organisms.
The ratio between the heavy and light isotopes of the element in their crystals is not quite right for stuff that has come out of the ground.
Instead, it matches the ratio found when organic molecules have been through a few rounds of biochemical processing.
Clearly there is a lot going on deep in the Earth that is completely unknown to science.
With a bit of luck, over the ten years of Dr Hazen's project, the veil of ignorance will be lifted a little.