What Form Did Carbon Exist in During the Formation of Earth?

[johnobirches]

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
Thanks
John

 

[Borek]

Plenty of carbon containing minerals - like carbonates - that can be produced in purely inorganic reactions.

 

[Bandersnatch]

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.

from:
http://news.harvard.edu/gazette/1996/07.11/NewCarbonCompou.html
(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:
http://en.wikipedia.org/wiki/Methane#Extraterrestrial_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.

 

[johnobirches]

Thanks folks - something for me to chew on.
John

 

[Astronuc]

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.

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/helfus.html#c1

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​

 

[Baluncore]

The CNO cycle uses C in two of it's steps. http://en.wikipedia.org/wiki/CNO_cycle
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.