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Earliest Carbon - What Form

by johnobirches
Tags: carbon, earliest, form
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Jan27-14, 08:10 AM
P: 2
Hi, I hope this question is appropriate for this forum - if not can anyone suggest a place to ask it?

There is a lot of carbon based matter around, on an in the earth. But,as I understand it, other than gaseous forms all the other liquid and solid forms have been generated/created by living organisms. This includes oil, coal, graphite, chalk, limestone as well as biomass.
Q. As earth formed in the early days of the solar system - where did all the carbon come from and in what form did it exist? If it was gaseous then what gas? and does that mean that earth formed with a ready made atmosphere?

Just wondering
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Jan27-14, 10:16 AM
Borek's Avatar
P: 23,733
Plenty of carbon containing minerals - like carbonates - that can be produced in purely inorganic reactions.
Jan27-14, 11:00 AM
P: 744
The element Carbon is fused in stars from lighter elements. All the carbon on Earth was once a part of some star that exploded and seeded its neighbourhood with most of the (reasonably stable) elements in the periodic table.
The atomic carbon in space can exist in a variet of molecular forms, all of which could be reasonably expected to end up on the primordial Earth:

The carbon finds would add to what Thaddeus calls a "stockroom of 110 familiar and unfamiliar chemicals" found in space by radio astronomers. They include water, alcohol, ammonia, carbon monoxide, carbon dioxide, and most recently, acetic acid, which gives vinegar its piquant flavor. Molecules such as ammonia and acetic acid, both of which contain carbon, can combine to produce amino acids, the basic building blocks of proteins.
(although I don't know why they say ammonia contains carbon...)

The outer gas giants and some of their satellites(most notably Titan) have atmospheres which include a few percent of methane:

After coalescing into a protoplanet, the geology(high temperature and pressure conditions) would take care of creating the remainder of carbon chemistry we have on Earth.

Jan27-14, 02:38 PM
P: 2
Earliest Carbon - What Form

Thanks folks - something for me to chew on.
Feb2-14, 05:04 AM
Astronuc's Avatar
P: 21,915
Main sequence stars like the sun have some carbon (and oxygen and nitrogen), which enables the CNO-cycle to contribute to some of the fusion in the star.

Carbon can be formed in the Triple Alpha Process in red giant and supergiant stars. If the central temperature of a star exceeds 100 million Kelvins, as may happen in the later phase of red giants and red supergiants, then helium can fuse to form beryllium and then carbon.

Red giants and supergiants can seed a galaxy with carbon. There are other fusion reactions that can form light elements.

Some fusion reactions for light elements. There are a number of other reactions the preclude these reactions, or rather compete with a different outcome, usually to lighter elements like He.

d + 4He -> 6Li + 1.7 MeV

d + 6Li -> 7Be + n + 3.4 MeV
-> 7Li + p + 5.0 MeV
t + 6Li -> 7Li + d + 0.9 MeV
-> 7Li + p + n - 1.2 MeV

3He + 4He -> 7Be + 1.5 MeV

3He + 6Li -> 7Be + d + 0.1 MeV

3He + 7Be -> 10C + 15.1 MeV
10C + n -> 11C (neutron capture)

4He + 7Li -> 11B + 8.5 MeV

4He + 7Be -> 11C + 7.5 MeV
11C + n -> 12C (neutron capture)

4He + 11B -> 14C + p + 0.8 MeV
-> 14N + n + 0.2 MeV
Feb4-14, 07:17 PM
Sci Advisor
P: 1,959
The CNO cycle uses C in two of it's steps.
But the CNO cycle is circular so on average it makes as much as it consumes.

Leakage of C from the CNO cycle can be a source of external C.
Any leakage from the cycle can be made up by alternative synthesis paths that make either C, N or O.

So 12C and 13C are both available from a stars normal activity.

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