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1. Abiogenesis

In the natural sciences, abiogenesis - also known as spontaneous generation - is the study of how life on Earth could have arisen from inanimate matter. This is also referred to as the "primordial soup" theory of evolution. On earth evidence is clear life began in water, such as some warm shallow sea or deep ocean thermal vent, as a result of the combination of chemicals from the atmosphere and the production of amino acids. These molecules in turn formed proteins, and a gradual cascade of ever more complex self-replicating molecules until cells formed. Ultimately all species trace their origin back to two or three original forms. Abiogenesis should not be confused with evolution, which is the study of how groups of already living things change over time. Most amino acids, often called "the building blocks of life", form via natural chemical reactions unrelated to life, as demonstrated in the Miller-Urey experiment and similar experiments simulating conditions of the early Earth. In all living things, these amino acids are organized into proteins, and the construction of these proteins is mediated by nucleic acids. How these organic molecules first arose and formed the first life is the focus of abiogenesis.

We have seen fairly complex biochemicals spontaneously form in simple simulations of earthly prebiotic conditions, such as in the Urey/Miller experiments yielding amino acids. Amino acids form in a wide variety of conditions. While many of the steps from inorganic matter to self-replicating life forms remain a mystery to us, much of the unfolding story after the development of multicellular organisms (metazoans) is found in earth's geologic fossil record and in comparisons of DNA genetic sequences. Abiogenesis (life from non life) is not actually a working theory yet, but when a workable mechanism is proposed it will be incorporated into the theory of evolution.

We know life arose very early in earth's history--within about the first billion years of its formation. Multicellular life, however, required another three billion years to form. The earliest multicellular forms (metazoans) were all marine organisms--creatures dwelling in earth's vast seas. Jawed vertebrates had evolved in these primordial oceans before the first amphibious vertebrates made their way onto land--even before the first terrestrial plants and insects.

2. Special Creation

According to this concept, all the different forms of life that occur today on planet Earth have been created by a God, gods, or extraterrestrial beings. This idea is found in the ancient scriptures of almost every culture. According to Hindu belief, Lord Brahma, the God of Creation, made the living world in accordance to his wish. According to the Christian, Jewish and Islamic belief, God created this universe, plants, animals and human beings in about six natural days. Others interpret the "six days" of Genesis as six epochs. The Sikh tradition says that all forms of life including human beings came into being with a single word of God.

Special creationists believe that the species have not undergone any significant change since they were introduced. Creationists generally accept a simplistic interpretation of The Bible's explanation that God created a number of basic groups of animals and plants as described in the first part of Genesis. They believe that while God created each group with the possibility of a good deal of variation, they were brought forth according to their own kind. By definition, the faith-based notion of Special Creation is purely a religious concept, acceptable only on the basis of faith. It has no scientific basis.

3. Biogenesis

The belief that living things come only from other living things (e.g. a spider lays eggs, which develop into spiders). It may also refer to biochemical processes of production in living organisms. The Law of Biogenesis, attributed to Louis Pasteur, states that life arises from pre-existing life, not from nonliving material. Pasteur's (and others') empirical results were summarized in the phrase Omne vivum ex vivo, Latin for "all life [is] from life", also known as the "law of biogenesis". Pasteur stated: "La génération spontanée est une chimère" ("Spontaneous generation is a dream"). It should be noted that the "spontaneous generation" Pasteur opposed referred to any modern, fully formed organism arising, NOT the original generation of life. In Pasteur's day it was commonly believed, for example, that flies spontaneously arose from piles of cattle dung, and necessarily because some fly laid its eggs there. Egyptians believed that mud of the Nile River spontaneously gave rise to many forms of life. The idea of spontaneous generation was popular almost until seventeenth century. Many scientists like Descartes, Galileo and Helmont supported this idea.

4. Theory of Chemical Evolution

This theory is also known as Materialistic Theory or Physico-chemical Theory. According this theory, the origin of life on earth is the result of a slow and gradual process of chemical evolution that probably occurred about 3.8 billion years ago. This theory was proposed independently by two scientists - A.I.Oparin, a Russian scientist in 1923 and J.B.S Haldane, an English scientist, in 1928.

5. Theory of Catastrophism

This theory on the origin of life is simply a modification of the theory of Special Creation. It states that there have been several creations of life by God, each preceded by a catastrophe resulting from some kind of geological disturbance. According to this theory, since each catastrophe completely destroyed the existing life, each new creation consisted of life form different from that of previous ones. French scientists Georges Cuvier (1769-1832) and Orbigney (1802 to 1837) were the main supporters of this theory.

6. Inorganic Incubation

Proposed by Professor William Martin, of Düsseldorf University, and Professor Michael Russell, of the Scottish Environmental Research Centre in Glasgow, this theory states that Instead of the building blocks of life forming first, and then forming a cell-like structure, the researchers say the cell came first and was later filled with living molecules. They say that the first cells were not living cells but inorganic ones made of iron sulfide and were formed not at the Earth's surface but in total darkness at the bottom of the oceans. The theory postulates that life is a chemical consequence of convection currents through the Earth's crust and, in principle, could happen on any wet, rocky planet.

7. Endosymbiotic Theory

This theory, espoused by Lynn Margulis, suggests that multiple forms of bacteria entered into symbiotic relationship to form the eukaryotic cell. The horizontal transfer of genetic material between bacteria promotes such symbiotic relationships, and thus many separate organisms may have contributed to building what has been recognized as the Last Universal Common Ancestor (LUCA) of modern organisms. James Lovelock's Gaia theory, proposes that such bacterial symbiosis establishes the environment as a system produced by and supportive of life. His arguments strongly weaken the case for life having evolved elsewhere in the solar system.

8. Panspermia - Cells From Outer Space

Some scientists believe that the simplest life-forms, whole cells (especially microbial cells), have been transported to the Earth from extraterrestrial sources. In this way, a process called panspermia (means seeds everywhere) might have initiated life on Earth. Most mainstream scientists have not supported panspermia, but early challenges have been thwarted in recent years due to discoveries such as terrestrial microbes that survive in extreme environments and incredibly aged yet viable microorganisms found in ancient rocks. In addition, water (essential for life) has been discovered on other planets and moons, and organic chemicals have been found on meteorites and in interstellar debris.

9. Cosmogony

Cosmogony is any theory concerning the coming into existence or origin of the universe, or about how reality came to be. In the specialized context of space science and astronomy, the term refers to theories of creation of the Solar System. For example, Greek mythology and some religions of the Ancient Near East refer to chaos, the formless or void state of primordial matter preceding the creation of the universe or cosmos in creation myths. Cosmogony can be distinguished from cosmology, which studies the universe at large and throughout its existence, yet does not inquire directly into the source of life or its origins.

10. Marine Theory

The Marine Theory suggests that life may have begun at the submarine hydrothermal vents; their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents are rich in chemical and thermal energy that sustains vibrant ecosystems.

11. Electric Spark Theory

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although subsequent research indicates the early atmosphere of Earth may have been poor in free hydrogen, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and lightning near eruption events would likely have been as common as it is now. Amino acids are also known to form spontaneously near deep ocean thermal vents, and in numerous other environments rich in organic material and energy.

12. Tribal and Mythological

Though not strictly scientific from our modern definition, ancient lore can be considered as the 'scientific' belief of its day, as it attempted to explain what was observed. From the tribes of ancient times to the mythologies of more modern cultures, there are countless stories of how life began. Some are based in pagan, or polytheistic, beliefs, while others are based on creation resulting from a single deity, or monotheism. This collection of myths, legend and tribal knowledge handed down over generations is the collective expression of how we humans attempt to explain our world and our place in it.

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โˆ™ 2014-05-13 21:33:03
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โˆ™ 2015-11-22 20:42:18

The two most widely-known are the tradition of Creation, and the theory of Evolution. According to the theory of Evolution, life developed by random processes, especially mutations.

The narrative of Divine Creation, which is contained in Genesis ch.1 and 2, states that God created the universe. This teaches us that God exists, that our lives and the world are not random, and that the created things may be assumed to contain vast wisdom in their beautiful and purposeful design. (In recent decades, this wisdom has indeed been partially revealed, through increasingly powerful microscopes.)Evolution through random mutations, on the other hand, may be understood as implying that life is an accident, that perceived beauty and wisdom are ultimately purposeless, and that our instinctive yearning for the Eternal is just an electrical impulse in our brain.

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Q: What are the different theories about the origin of life?
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