Timeline Earth Life

Timeline for life in billions of years (Ga): click to enlarge image.

Based on radio-dating of meteorites, the solar system is about 4600 Ma – 4600 million years, or 4.6 billion years old (Ga). The formation of the earth occurred 10 Ga after the Big Bang. The sun and planets condensed from a large, hot accretion disk.

The earliest atmosphere of H2 and He was lost to space, and was replaced by a reductive atmosphere with a composition probably similar to outgassing of modern volcanoes – H2O, CO2, SO2, S2, Cl2, N2, NH3, and CH4.

Oxygen levels began to rise after the evolution of oxygenic photosynthesis by the Cyanobacteria, which evolved at least at least 3450 million years ago (3.45 Ga) and formed the earliest microfossils as stromatolite reefs.

There is considerable evidence that the earliest eukaryotes evolved through serial endosymbiosis. Chloroplasts resulted from endosymbiotic transfers of Cyanobacteria, and mitochondria originated from endosymbiotic transfers of alpha-proteobacteria (purple bacteria). Mitochondria are the site of oxidative phosporylation in eukaryotes.

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"Peribiotic" conditions?

Frozen:
The prebiotic synthesis of pyrimidines in frozen solution.
Most prebiotic syntheses depend on the reaction of concentrated precursor compounds to produce bio-organic molecules. It is now believed that the early Earth's atmosphere was not reducing enough to have permitted copious synthesis of precursor molecules. Freezing allows reaction to occur even from dilute solution. This reaction has been demonstrated for the purines but not for the pyrimidines. It is shown here that dilute solutions of simple prebiotic molecules produce the biological pyrimidines cytosine and uracil upon freezing. Cold environments may have allowed synthesis of all of the RNA bases even from low organic yielding atmospheres, such as those of the early Earth, Mars, Titan and Europa.

Cleaves Ii HJ, Nelson KE, Miller SL. The prebiotic synthesis of pyrimidines in frozen solution. Naturwissenschaften. 2006 May;93(5):228-31. Epub 2006 Mar 22.

The cold origin of life: B. Implications based on pyrimidines and purines produced from frozen ammonium cyanide solutions. [Orig Life Evol Biosph. 2002]

Pre-biotic molecular synthesis
Current status of the prebiotic synthesis of small molecules. [Chem Scr. 1986] PMID: 11542054
Titan: a laboratory for prebiological organic chemistry. [Acc Chem Res. 1992] PMID: 11537156
Prebiotic synthesis of diaminopyrimidine and thiocytosine. [J Mol Evol. 1996] PMID: 8995051
An efficient prebiotic synthesis of cytosine and uracil. [Nature. 1995]
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Hot
Amino acids on the rampant primordial Earth: electric discharges and the hot salty ocean.
For more than 50 years scientists who study prebiotic chemistry have been dealing with chemical evolution as it could have possibly taken place on the primordial Earth. Since we will never know what processes have really taken place around 3.8 to 4 billion years ago we can only come up with plausible reaction pathways that work well in an early Earth scenario as indicated by geochemists. In our work we have investigated the plausibility of one particularly important branch of prebiotic chemistry, the formation of amino acids, by electric discharge in a neutral atmosphere composed of carbon dioxide, nitrogen, and water vapour above liquid water. We have found yields of various amino acids under different temperature conditions, with and without sodium chloride in a simulated primordial lake or ocean within extremely short reaction times compared to the timespan available for prebiotic evolution.
Plankensteiner K, Reiner H, Rode BM. Amino acids on the rampant primordial Earth: electric discharges and the hot salty ocean. Mol Divers. 2006 Feb;10(1):3-7.


A hydrogen-rich early Earth atmosphere. [Science. 2005] PMID: 15817816
The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds. [Adv Space Res. 1983] PMID: 11542461
Current status of the prebiotic synthesis of small molecules. [Chem Scr. 1986] PMID: 11542054
Impact melting of frozen oceans on the early Earth: implications for the origin of life. [Proc Natl Acad Sci U S A. 1994] PMID: 11539550
Prebiotic chemistry in clouds. [J Mol Evol. 1991] PMID: 11538260 See all Related Articles...

Hot vs Cold
Evolving lipid vesicles in prebiotic hydrothermal environments.
We compared three different kinds of lipid vesicles made of saturated fatty acids, unsaturated fatty acids, and phospholipids for their evolutionary capabilities in a simulated hydrothermal environment.Encapsulation of the glycine monomers enhanced the oligomerization of peptides in all cases. Fatty acid vesicles remained stable at higher temperatures and efficiently utilized heat energy for this synthetic reaction. Phospholipid vesicles were destabilized by higher temperatures, and thus were found to be better suited to enhance synthetic reactions at lower temperatures.
Furuuchi R, Imai E, Honda H, Hatori K, Matsuno K. Evolving lipid vesicles in prebiotic hydrothermal environments. Orig Life Evol Biosph. 2005 Aug;35(4):333-43.


Kinetic studies of the interaction of fatty acids with phosphatidylcholine vesicles (liposomes). [Colloids Surf B Biointerfaces. 2006] PMID: 16466910
Prebiotic oligomerization on or inside lipid vesicles in hydrothermal environments. [Orig Life Evol Biosph. 2002] PMID: 11889914
Reaction behaviors of glycine under super- and subcritical water conditions. [Orig Life Evol Biosph. 2002] PMID: 11889913
Formation of peptide bonds from metastable versus crystalline phase: implications for the origin of life. [Orig Life Evol Biosph. 2000] PMID: 11196575
Construction of protocellular structures under simulated primitive earth conditions. [Orig Life Evol Biosph. 1988] PMID: 3226717 See all Related Articles...

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Climate and Extinction

Pounds et al[2] defined an "extinction" as the time when a frog species was last observed by professional teams of herpetologists working in these regions. Most extinctions (78% to 83%) occurred in years that were unusually warm across the tropics. The likelihood that this correlation arose by chance is less than one in a thousand. Moreover, the observed patterns of extinction vary with altitude -- as do the effects of climate change.

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