Chemistry of Life (Origin of the Elements). ASTR 1420 Lecture #3 Section 3.2 & 5.3. There are 103 elements known to exist. Yet, all known life forms are mainly based on C, H, O, & N, and most advanced organisms are using H 2 O! Why?
Section 3.2 & 5.3
Yet, all known life forms are mainly based on C, H, O, & N, and most advanced organisms are using H2O! Why?
Why shouldn’t there be life forms with iron skeleton and using methanol?
After Big Bang, lightest elements (H, He, Li, Be) were created, but only for a limited time period (3 to 20 minutes).
92% H + 8% He and almost no other elements.
Hydrogen burning :
4 Hydrogens Helium + energy
US yearly energy consumption:
= can light Sanford stadium for 100 billion years!
= can be produced from a fusion of mere 80lb of Hydrogen!
Not much Li (H+He), Be, B (Be+H or He+Li)…
Therefore, if one wants to make something out of the current mix of elements in the Universe, the most efficient outcome will be a compound of H, O, C, N.
2, 10, 18, etc.
covalent bond : sharing an electron (s)
Ionic bond : Example of a chemical bonding that makes up salt
H + F Hydrogen Floride
Na + Cl Sodium Chloride (salt)
or 2H + O H2O
After many, many recycles
Noble gases (he, Ne, Ar, etc.) do
not participate in chemical reactions.
(right figure) chemical composition of the human body by weight.
Oxygen mostly in H2O
Cell structures and their functions are due to Carbon Carbon-based life!
Any chemical compounds contain C “organic compound”
Requirements for the base element:
Let’s consider all different ways of combining with Hydrogen…
E.g., C90H84 or C167H336, …
# of possible isomers for C167H336 = 9×1083
? Can this may be due to the difference in the maximum number of bondings for C (No=4), O (No=2), N (No=3)?
Entirely made of Carbon. (superconductor material, etc.)
For example, CH4 (methane), SiH4 (silane).
Although life based on silicon may be possible, it will be extremely uncommon at best!
Life based on carbon seems favored as the dominant kind of life in the Universe!
Is water (H2O) inevitable?
Solvent : dissolve other chemical compounds (to transport nutrients and wastes in the cells) other advanced alien life forms are very likely use solvent in their metebolism
At low temperature, chemical reactions are slower hence slower metabolism.
Any worlds meet the #3 requirement, likely meet the first two requirements also. Why?
A habitable world = only if it has a liquid water!
Cosmic abundance (nuclear synthesis)