Earth before life

Meanwhile, the contraction of the cloud causes its rate of rotation to speed up (rotate a conker on the end of a string— as you shorten the string, the rate of rotation increases). This, so the theory goes, produces a tendency for some of the condensing material to be thrown back into space. So not all of it would condense to form the star. This uncondensed material would remain in regions far from the star and would probably take part in separate condensations, sweeping up solid dust particles and gas left in the shrinking 

One of these secondary condensations resulted in the appearance of the earth some 4.5 billion years ago, according to two independent assessments of the earth s age (meteorite age determination and measurement of lead isotope ratios from terrestrial rocks ). What condition the earth would have been in is a matter of conjecture. Was it hot or cold Arguments have been put forward to support either condition. But it appears that earlier in its history, the planet was subject to greater volcanic activity than it is now. 

It is generally agreed that the early atmosphere was a reducing one and most likely consisted of water, methane, carbon dioxide, and nitrogen, 

The mechanism by which amino acids are made seems to involve the prior formation of hydrogen cyanide and aldehydes, which then react with ammonia and water to form amino acids. It is possible to synthesise practically the whole range of amino acids necessary for life by adding small 

So far, all the prime constituents of nucleic acid synthesis have proved surprisingly easy to prepare by prebiotic synthesis. What has proved difficult has been the synthesis of nucleosides (organic bases and sugars 

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We do not know the extent to which the Murchison organics reflect what was available on early Earth before life emerged. The rich inventory of amino acids does not appear to be universal in carbonaceous chondrites (although the number that have been examined in detail is very small). For example, only a few amino acids (glycine, alanine, a-aminoisobutyric acid, a-amino-n-butyric acid, y-aminobutyric acid) are found in the meteorite that fell in 2000 on Tagish Lake, Canada (Table 5.3).7 The near absence of complex amino acids is significant, inasmuch as the meteorite was captured in a pristine condition soon after it fell. 

Another interesting point about sulfide minerals is that they could be related with the beginnings of live in our planet. In fact, acetic acid has been synthetized in sulfide surfaces in conditions simulating Earth before life." Some researchers proposed a theory that life could be started with the amino acids condensation catalyzed by sulfide surfaces, in deep regions of ocean, under high pressures, and close to thermal fountains." "... 

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Robert A.Goyer, appointed by the Division on Earth and Life Studies, who was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution. 

Mojzsis SJ, Arrhenius G, McKeegan KD, Harrison TM, Nutman AP, Friend CRL (1996) Evidence for life on Earth before 3,800 million years ago. Nature 384 55-59 Mozely PS (1989) Relationship between depositional environment and the elemental composition of early diagenetic siderite. Geology 17 704-706... 

Prebiotic Occurring before life appeared on Earth... 

The opportunity to study isolated molecules also offers an avenue into questions of prebiotic chemistry. To determine the rules of chemistry that may have been important on an early earth, before the onset of life, one needs to observe interactions between biomolecular building blocks in the absence of biology. 

Approximately 1 billion years after Earth s formation, life appeared, as already mentioned. Before life could exist, though, another major process needed to have taken place—the synthesis of the organic molecules required for living systems from simpler molecules found in the environment. The components of nucleic acids and proteins are relatively complex organic molecules, and one might expect that only sophisticated synthetic routes could produce them. However, this requirement appears not to have been the case. How did the building blocks of life come to be ... 

Eons ago. The atmosphere of the primitive Earth before the emergence of life contained N2, NH3, H2, HCN, CO, and H2O. Which of these compounds is the most likely precursor of most of the atoms in adenine Why ... 

Did you know that the atoms of carhon, nitrogen, and other elements in your body are far older than you In fact, they ve been around since before life began on Earth. The amount of matter on Earth never changes. As a result, it must be recycled constantly. You learned about the water cycle earlier in the chapter. A number of elements cycle through the environment in similar, distinct pathways. 

The world before life - the prebiotic world - is a place where some very complex chemistry must have taken place. But how did it all start There have been two fruitful lines of enquiry -one assuming that life started with only those molecules which were naturally occurring in the oceans and atmosphere. The other approach looks outside the Earth. 

In the study of chemical evolution we are interested in the path by which molecules of biological significance could have been formed on the earth before the appearance of life. We have therefore examined the action of electric discharges on the presumed primitive atomsphere of the earth. Three different sets of experiments were performed (1) with methane, ammonia, and water (2) with methane and ammonia (3) with methane alone. Several molecules of biological significance have been synthesized. In some instances polymerization appears to have taken place. These results may be relevant to the Oparin-Haldane hypothesis of chemical evolution. 

Before life appeared on earth, there were two possible sources of organic molecules on the early earth ... 

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