Scientists have told, how on Earth did life

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Ученые рассказали, как на Земле появилась жизньIt turns out that the fall of a large meteorite in the lake could lead to the emergence of life on our planet.

RNA molecules, may be responsible for the appearance of the first life on Earth, could first be formed in warm, shallow waters on the planet’s surface.

An international team of scientists from Canada and Germany have simulated processes that could occur in such reservoirs and has concluded that the nitrogenous bases in this case was to get to the Ground in a collision with meteorites.

The paper was published in the Proceedings of the National Academy of Sciences.

One hypothesis of the origin of life on Earth is the RNA world model, according to which one of the first stages of the emergence of life on Earth was the stage when the genetic information encoded in the form of ribonucleic acids. However, plausible mechanisms for the formation of the first RNA molecules while was proposed. Unknown sources of nitrogenous bases on Earth, which, most likely, at this time was neutral, not reducing atmosphere nor the exact way of formation of nucleotides and polymerization of them are ribonucleic acids.

Now, there are two main hypotheses, which formed RNA: could this happen in the hydrothermal springs in the oceans or in the warm shallow waters on the Earth’s surface. The second hypothesis is more likely due to the fact that inside the ocean is not necessary for the polymerization of cyclic change of dry and wet seasons.

In his new work an international team of scientists from Canada and Germany studied the possible formation of RNA molecules in small surface waters for the most likely ranges of conditions on the Ground in Calarasi period (approximately from 4.5 to 4 billion years ago). Accurate temperature, which was on the planet at this time unknown, that is why scientists are considering two possible options: around 20 degrees Celsius (the model of “warm” Protozilla) and about 65 degrees (model a hot Protozilla). However, due to the lack of the ozone layer was sufficiently high levels of ultraviolet radiation. As possible sources of nitrogenous bases, scientists have considered the interplanetary dust and meteorites, rock samples which have been able to find traces of adenine, uracil and guanine.

Given all these conditions, scientists have modeled the process of changing conditions in the reservoirs during the year as a result of precipitation and evaporation and infiltration of fluid into rock. Depending on temperature and rainfall, could have formed several stationary regimes of temperature fluctuations and water level in reservoirs, but all of them were pronounced seasonal fluctuations. Such fluctuations have led to the fact that depending on the season for the nitrogen base dominated or hydrolysis reaction, or the reaction of photodissociation.

It turned out that seasonal fluctuations can indeed lead first to the formation of nucleotides and their polymerization to RNA molecules. While the original source of the nitrogenous bases have to be meteorites, the number of which in the era of late heavy bombardment was sufficient for delivery to Earth required number of bases.
The most favorable conditions for the formation of RNA molecules are temperatures from 50 to 80 degrees Aim, which confirms the model of “hot” Protozilla. At such temperatures the whole formation process of RNA is only a few years: first, a nitrogenous base, came to Earth with meteorites, react with ribose and phosphorus sources with the formation of nucleotides. According to the model, this process takes 2 or 3 years. After that, 1-2 seasonal cycle is polymerization of nucleotides. This high speed does not give the resulting system to recover and destroy all of the resulting RNA, e.g., as a result of another meteorite impact.

Despite the apparent slimness of the proposed model, it has obvious shortcomings. So according to John Sutherland, who proposed in 2009 a new path abiotic synthesis of ribonucleotides on Earth, this mechanism has at least two problems. First, a very high probability of decomposition of nitrogenous bases in the collision of a meteorite with the Earth, because the temperature reaches 2300 degrees Celsius. Secondly, the ground conditions may not be sufficient to direct formation of the ribonucleotides of the nitrogenous bases and ribose, and is now believed that this occurred by other mechanisms.

If the hypothesis still holds true, based on the number of have fallen to the Ground meteorites, the RNA world could have appeared on Earth later, 200 million years after conditions on earth became suitable for life. On the other hand, in a recent paper a group of scientists from the Czech Republic expressed the hypothesis that the composition of the atmosphere on Protozilla in some point was the recovery and contained a large amount of carbon monoxide, ammonia and methane. And from this atmosphere the nitrogen base could be formed and directly on the Ground.

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