According to the Bible, God created the first man, Adam, from the soil and the first woman, Eve, from Adams rib. These events happened in the Garden of Eden almost six thousand years ago. That is one of the many beliefs of how carbon based life forms, otherwise referred to as living organisms, came to exist on Earth. Since the beginning of mans reign on earth he has tried to explain his origins. He has used various religions and myths of being created by some higher power and he has looked toward the stars and planets thinking that perhaps life came to earth by way of space ship or meteorite. Even in todays world of high technology we have yet to answer that age-old question, but scientists are closer than they have ever been before.
Scientists from many different fields have been researching our beginnings and they have many different theories of how we came to exist. One of those theories is that life originated at the bottom of the ocean near an underwater hydrothermal vent.
Hydrothermal vents are created when the earths crust on the ocean bottom spreads apart. The earths surface is made up of crustal plates that are continuously moving together at some points and apart at others. The hydrothermal vents or black smokers, so called because of the dark plumes arising from the vents like chimneys, are places where heat is transferred from the lithosphere to the ocean (Parson 1995). Jack Corliss first discovered hydrothermal vents in 1977 while exploring a volcanic ridge in the Pacific Ocean (Simpson 1999). Up until the discovery of the vents scientist believed that the ocean floor was primarily lifeless because of the water pressure, the cold temperature, and the lack of oxygen.
What Jack discovered was a thriving ecosystem consisting of various sea creatures including mussels, tubeworms, clams, and shrimp living around vents that were expulsing water at temperatures up to 350 degrees Celsius out of the earths interior (Simpson 1999). Because of the water pressure the high temperature was not as dangerous to the animal life as it would have been on the surface. Many of the hydrothermal vent animals consist of entire groupings of animals that only exist at the vents. The fauna is endemic at high taxonomic levels, including a class, an order, five super-families, eight families, and numerous genera. The distinctiveness shows a period of long evolution and many show origins from the Mesozoic or earlier. It has been determined that these creatures are living off of microbes that come from the interior of the earth. These microbes convert carbon dioxide, water, and nitrate into a usable organic food source in much the same way a plant uses photosynthesis to convert elements into its food source (Humphris 1995).
The creatures acquire their oxygen source from iron oxides and sulfates, which consist of weakly bound oxygen and other elements (Gold 1999). Many scientists now believe that life could have developed around these vents where photosynthesis does not supply the energy source. On the bottom of the ocean the first organisms would have been protected from extreme radiation from the sun and space and would have survived any organism sterilizing events such as crashing meteorites.
In order for life to have begun certain elements would have to have been present in the environment. These elements are believed to have been present on the surface of the early earth and now are equally believed to be present at the hydrothermal vent sites in some form. These elements include carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus (Fox 1972). These basic elements and others plus the intense heat from the lithosphere discharge would have been sufficient to create the chemical reactions necessary to form the first amino acid which in time became the first proto-cell which in time became the first cell and so forth. How exactly this happened is yet unknown and will never truly be known. Scientists can only speculate on and produce theories about what really happened. Two such theories that have arisen from the hydrothermal vent research are Michael Russell and Allan Halls theory and Gunter Wachtershausers theory.
Michael Russell and Allan Halls theory is based on iron-sulfur groups, which is an essential electrochemical catalyst in living cells (Russell 2000). They believe that the precipitation of chemical solutions from the hydrothermal vents could have formed a barrier around itself that would prevent further mixing, provided a template for organic molecule chains, and acted as an electrochemical catalyst. Their protected precipitate concentrated organic molecules like amino acids and dissolved chemicals, which reacted from rocks containing iron-rich minerals (Russell 2000). After time this barrier evolved into a cell membrane with organic molecules. This cell membrane could then chemically bond to and assemble a sequence of molecular components of RNA.
From there the RNA could turn the amino acids into proteins which then could become DNA. With the help of hydrogen and methane, both of which are found in the hydrothermal vents, the new large molecule could carry out reproduction without the further help of the iron-sulfur template. These new cells could then survive using carbon from carbon monoxide, methane, or carbon dioxide dissolved in the warm saltwater of the vents. They could also receive chemical energy from linking hydrogen and ferric iron (Russell 2000).
Gunter Wachtershausers theory is based on metallic ions from sulfides. These metallic ions acted like todays enzymes and formed the first organic molecule of acetic acid from a combination of carbon, hydrogen, and oxygen. Acetic acid plays a vital role in metabolism today. Wachtershauser believes that metabolism developed before any other cellular function (Simpson 1999). Wachtershausers theory focuses on the citric acid cycle which he believes was similar to the chemical reactions that began life except the heat loving microbes of the hydrothermal vents operated the cycle backwards. Instead of giving off carbon dioxide they incorporated carbon atoms to create more complex molecules which later evolved into cells (Simpson 1999).
The theory of life beginning on the ocean bottom has also rekindled interest in the theory of life on other planets. Many believe that if life did originate around a hydrothermal system here on earth then the same could have happened on other planets that contained oceans and hydrothermal activity. Scientists believe that Mars at one time contained the right environment for such activity. Europa, one of Jupiters moons, is also thought to fit the requirements.
Scientists will never know for sure how life started on earth some four billion years ago. They may discover ways that life could have evolved but there is no way of knowing for sure. Since scientists can not be certain what the early earth was like; what chemical reactions occurred on a daily basis; and how much radiation, meteorites, and rain attacked the surface they can not know for sure the requirements that the first organisms had to meet. One thing they do know is that the chemical make up of the earths surface, oceans, and atmosphere were not like they are today. We breathe oxygen today because the ancestors of todays organisms evolved from using a purely chemical reaction to obtain its energy to photosynthesis that produced oxygen as a side effect.
With todays overpopulation, food shortages, and limited natural resources in most parts of the world we are once again turning to the ocean for our energy sources. It has been said that history repeats itself. Could it be possible that we will one day return to depending on the ocean for our actual survival? Could we once again return to the hidden Garden of Eden?
Bibliography:
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