Summarize the three (3) current competing theories of the origin of life on Earth: it arrived from an extraterrestrial source, it originated as a heterotroph, it originated as an autotroph.

Summarize the three (3) current competing theories of the origin of life on Earth: it arrived from an extraterrestrial source, it originated as a heterotroph, it originated as an autotroph.


The answer to the question of the origin of life is a puzzle that scientists to this day cannot solve. Yet with continual research, scientists find evidence that will one day bring a solution. At present, there are three competing theories of how life came on Earth. All these theories but one of them states that life arrived here from an outside source. Swedish scientist Svante Arrhenius popularized the idea of panspermia in the early nineteen hundreds; this is the concept that life arose outside the Earth and that living things were transported to Earth to seed the planet with life. According to the passage, this theory does not explain how life arose originally and had little scientific support at that time.

Arrhenius’ theory however has been revived and modified after gaining new evidence from the examinations of meteorites and space explorations. Organic molecules are found in many meteorites, and this suggests that life may have existed elsewhere in the solar system. An analysis of a meteorite found in Antarctica in 1996 suggested that from its chemical make-up, it was a portion of Mars; also the presence of complex organic molecules and small globules resembled those found on earth. At the current moment, most scientists no longer agree that their structures are from microorganisms, but there are still groups of scientists who still believe that they are.

Another hypothesis for the origin of life focuses on spontaneous generation. Spontaneous generation is the concept that living things arise from nonliving material. Aristotle proposed this concept between 384-322 B.C. and it was widely accepted until the seventeenth century. Many scientists support the idea that first living things on Earth were heterotrophs, which lived off organic molecules in the ocean. There is evidence to suggest that a wide variety of compounds were present in the early oceans, some of which could have been used, unchanged, by primitive cells. Because the earliest cells appear in the fossil record before any evidence of oxygen in the atmosphere, these early heterotrophs would have been anaerobic organisms. According to the heterotrophic hypothesis the first living beings were very simple organisms, i.e., not producers of their own food, which emerged from the gradual association of organic molecules into small organized structures (the coacervates). The first organic molecules in their turn would have appeared from substances of the earth’s primitive atmosphere submitted to strong electrical discharges, to solar radiation and to high temperatures.

Although the heterotrophic hypothesis for the origin living things was the prevailing theory for many years, recent discoveries have caused many scientists to consider an alternative that leads to the third hypothesis of how Earth came to be. Research from these scientists show that the first organism may have been was an autotroph, an organism that is able to form its food from simple inorganic substances such as carbon dioxide. Much evidence shows that the Earth was a much hotter place in the past than it is currently. The fact that today many members of the domain Archaea live in very hot environment suggest many originated on Earth, however at a temperature that was much hotter. If the first organisms were autotrophs, there would been competition among different cells for the inorganic raw materials they needed for their metabolism, and then mutations occurred.

Scientists still do not know how life on Earth originated, but through analysis of evidence and continual to exploration to gain more knowledge they gain more insight. Currently there are three competing theories of the origin of life on Earth.1 Life arrived here from an extraterrestrial source. 2: Life originated on Earth as a heterotrophy. 3: Life originated on




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