5 ms·
You're absolutely right that, if we define life generally as a self-replicating system implemented in chemistry, there is no a priori reason to assume that extr
by subnaught 12y ago
You're absolutely right that, if we define life generally as a self-replicating system implemented in chemistry, there is no a priori reason to assume that extraterrestrial life would use the same elements as we do. However, there are a couple good reasons that this might be the case:
Abundance - Broadly speaking, the prevalence of an element decreases with its atomic mass, which means that, while elemental availability will differ from planet to planet, lighter elements will always be more abundant. Thus, statistically speaking, it is likely that extraterrestrial life uses C,H,N,O just as we do.
Bonding - When you study the chemical bonding of elements in relation to their position in the periodic table, what you realize is the "first row," i.e. C,N,O, is actually an exception and the rest of the periodic table is the rule. What this means in practice is that these elements are capable of a much greater diversity in bonding than those below. It is this diversity that allows for the development of the complex biomolecular machinery necessary for life.
Edit: Here's a great essay by Nobel laureate Roald Hoffmann on the differences between Si and C and the implications for life: http://pubs.acs.org/cen/80th/print/silicon.html http://pubs.acs.org/cen/80th/print/silicon.html
- ars 12y agoIt's more than just light elements, those elements are the main sequence elements made by Stellar nucleosynthesis. If you look here, you'll see just how abundant they are compared to everything else: https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...
- jonalmeida 12y agoBeen a while since chem & physics class for me as well. How are these estimations calculated, and to what certainty? Surely, these are calculations only from the observable universe?
- ars 12y agoI'm not sure how they know, but see here: https://en.wikipedia.org/wiki/Stellar_nucleosynthesis https://en.wikipedia.org/wiki/Stellar_nucleosynthesis for the reason for the quantities.
- bsurmanski 12y agoI'm not a scientist, but I imagine that they would use the emission spectrum[0] of the various elements. Perhaps they could sample the spectrum of all of the stars and that might give a reasonable approximation. [0] http://en.wikipedia.org/wiki/Emission_spectrum http://en.wikipedia.org/wiki/Emission_spectrum
- mjfl 12y agoThey do it using spectral analysis. Different elements have different absorption bands of light. You can look at a graph of light from a star, with intensity of light on the y-axis and frequency/wavelength (color) on the x-axis and that tells you quite a bit about the composition of the star.
- ars 12y agoThat only tells you the composition of the surface of the star. The heavier elements will be deeper. I suspect there is mathematical modeling. Interstellar dust might provide the spectrum instead of stars, although that really only tells us the composition of the milky way.
- mjfl 12y agoWell, in order to find the composition of interstellar dust, they will use spectral analysis as well...