At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
Well what do you know about the conditions of early earth? :)
I agree with TraceNove. Think about the conditions of the atmosphere (gas composition) and I guess you can answer that question alone.
http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html Biological Evidence Chemical building blocks of life could not have formed in the presence of atmospheric oxygen. Chemical reactions that yield amino acids are inhibited by presence of very small amounts of oxygen. Oxygen prevents growth of the most primitive living bacteria such as photosynthetic bacteria, methane-producing bacteria and bacteria that derive energy from fermentation. Conclustion - Since today's most primitive life forms are anaerobic, the first forms of cellular life probably had similar metabolisms. Today these anaerobic life forms are restricted to anoxic (low oxygen) habitats such as swamps, ponds, and lagoons.
The early earth It is believed that the Earth was formed about 4.5 billion years ago. Heavy bombardment by rubble ceased about 3.8 billion years ago. Reducing atmosphere: much free H also H2O, NH3, CH4 little, if any, free O2 with numerous H electrons, require little energy to form organic compounds with C Warm oceans, estimated at 49-88°C Lack of O2 and consequent ozone (O3) meant considerable UV energy Chemical reactions on early earth UV and other energy sources would promote chemical reactions and formation of organic molecules Testable hypothesis: Miller-Urey experiment simulated early atmospheric conditions found amino acids, sugars, etc., building blocks of life won Nobel prize for work experiment showed prebiotic synthesis of biological molecules was possible Issues Miller later conceded that the conditions in his experiments were not representative of what is currently thought to be those of early earth He also conceded that science has no answer for how amino acids could self-organize into replicating molecules and cells In the 50 years since Miller-Urey, significant issues and problems for biogenesis have been identified. This is a weak hypothesis at this time. Conclusion: Life exists, we don't know why. Origin of cells Cells are very small and decompose quickly after death. As such, fossils of the earliest cells do not exist. Scientists have had to form a variety of theories on how cells (and hence life) was created on Earth. Bubble hypothesis A. Oparin, J.B.S. Haldane, 1930’s Primary abiogenesis: life as consequence of geochemical processes Protobionts: isolated collections of organic material enclosed in hydrophobic bubbles Numerous variants: microspheres, protocells, protobionts, micelles, liposomes, coacervates Other surfaces for evolution of life deep sea thermal vents ice crystals clay surfaces tidal pools The RNA world? DNA → RNA → polypeptide (protein) Catalytic RNA: ribozyme discovered independently by Tom Cech and Sid Altman (Nobel prize) catalytic properties: hydrolysis, polymerization, peptide bond formation, etc. Self-replicating RNA molecule may have given rise to life consistent with numerous roles for RNA in cells as well as roles for ribonucleotides (ATP) relationship to bubble-like structures is uncertain The earliest cells Microfossils ~3.5 by resemble bacteria: prokaryotes biochemical residues stromatolites Archaebacteria (more properly Archaea) extremophiles: salt, acid, alkali, heat, methanogens may not represent most ancient life Eubacteria cyanobacteria: photosynthesis atmospheric O2; limestone deposits chloroplasts of eukaryotes http://en.wikibooks.org/wiki/General_Biology/Print_version
http://www.originoflife.in/section-3-resemble-bacteria.htm Mitochondria and chloroplasts resemble bacteria closely in several aspects; actually this was the theoretical basis for their endosymbiont origin. Any organism or a membrane-bound structure with limited genetic material in it resembles each other because their genomes do not contain redundant, non- coding sequences resulting in the formation of a circular DNA. They have some genetic resemblance also because, after all, the bacterial membrane and the eukaryotic membrane (and ultimately the organelle’s membrane) descended from a common ancestor. Their metabolism is also simple and stereotyped, thus the resemblance.
http://en.wikipedia.org/wiki/Stromatolite Stromatolites were much more abundant on the planet in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia. The earliest stromatolite of confirmed microbial origin dates to 2.724 billion years ago. A recent discovery provides strong evidence of microbial stromatolites extending as far back as 3.450 billion years ago.
http://www.newagepublishers.com/samplechapter/001079.pdf Formation of Polymers
We have seen that it was possible to synthesise polypeptides in the atmosphere of prebiological earth through spontaneous generation. There is yet another biopolymer, nucleic acid, that imparts the character of self-regulation to the living organisms. The building blocks of nucleic acids are mononucleotides, consisting of nitrogenous bases, ribose or deoxyribose sugar and a phosphoric acid group. We have now evidence to suggest that nucleic acids and nucleotides could be obtained by simulating conditions prevalent on the primeval earth. Simulation experiments using appropriate bases and pentose sugars have demonstrated that nucleosides can be produced and mononucleotides can be synthesised by heating or subjecting the nucleosides to ultraviolet radiation in the presence of phosphoric esters. Loharmann, Bridson and Orgel (1980) were able to demonstrate polymerisation of nucleotides on nucleic acid templates in enzyme-free systems. Thus nucleotides could have originated abiotically on the primitive earth. http://www.newagepublishers.com/samplechapter/001079.pdf page 7
Protobiont : The Primitive Form of Life
Protobionts are systems that are considered to have possibly been the precursors to prokaryotic cells. If RNA is trapped inside, the system can use the RNA or select for it.
http://www.biocab.org/protobiont.html Scientists think that the protobionts are the evolutionary precursors of prokaryotic cells. Protobionts may be originated as an array of microspheres of diverse organic and inorganic compounds enclosed by lipidic membranes. Proteins, carbohydrates, lipids, and other organic substances were the most important autocatalytic organic compounds. Water was a very important factor in the assembly of the protobionts' endoplasm. After this event, several microspheres could self-organize into organelles that were able to perform specific functions; for example, lysosomes, peroxysomes, vacuoles, etc. Gradually, some segments of the external membrane would invaginate for forming membranous organelles, like endoplasmic reticulum and Golgi apparatus. First protobionts would not have a nucleus membrane (nuclear envelope); consequently, they could be identified like prokaryotes. http://brownapreview.wikispaces.com/Evolution http://www.biology.iupui.edu/biocourses/N100/ch8life.html