Sabtu, 23 Juni 2012

List o’ 10 Scientific Theories of How Life on Earth Began

List o' 10 Scientific Theories of How Life Began
The bottom line is that there is really just no way to know for sure, but the scientific approach has provided many theories based on observation and explanation. Faith-based theories present the explanation in different terms, though still attempting to take a “socially scientific” basis. In short, many theories based on hard science address the first appearance of cell based life – this list presents 10.

10. Tribal and Mythological

List o' 10 Theories of How Life Began
Though not strictly scientific from our modern definition, ancient lore was believed to be a scientific belief in their 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 beliefs, while others are based on creation resulting from a holy deity. This collection of myths, legend and tribal knowledge handed down over generations is the collective expression of how man attempts to explain his world and his place in it.

9. Cosmogony

List o' 10 Theories of How Life Began - 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.

8. Panspermia – Cells From Outer Space

List o' 10 Theories of How Life Began - Panspermia

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.

7. Abiogenesis

List o' 10 Theories of How Life Began - 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 (life began in water as a result of the combination of chemicals from the atmosphere and some form of energy to make amino acids, the building blocks of proteins, which would then evolve into all the species).  It 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”, can form via natural chemical reactions unrelated to life, as demonstrated in the Miller–Urey experiment and similar experiments, which involved simulating the 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. Which of these organic molecules first arose and how they formed the first life is the focus of abiogenesis. [wikipedia] Egyptians believed that mud of the Nile river could spontaneously give rise to many forms of life. The idea of spontaneous generation was popular almost till seventeenth century. Many scientists like Descartes, Galileo and Helmont supported this idea.

6. Endosymbiotic Theory

List o' 10 Theories of How Life Began - Endosymbiosis

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 recognised 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.

5. Inorganic Incubation

List o' 10 Theories of How Life Began - 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 sulphide 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.

4. Theory of Catastrophism

List o' 10 Theories of How Life Began - 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.

3. Theory of Chemical Evolution

List o' 10 Theories of How Life Began - 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.

2. Faith-based Creation

List o' 10 Theories of How Life Began - Christian Creation Theory

According to this theory, all the different forms of life that occur today on planet earth, have been created by God, the almighty. This idea is found in the ancient scriptures of almost every religion. According to Hindu mythology, Lord Brahma, the God of Creation, created the living world in accordance to his wish. According to the Christian belief, God created this universe, plants, animals and human beings in about six natural days. The Sikh mythology says that all forms of life including human beings came into being with a single word of God. Special creation theory believes that the things have not undergone any significant change since their creation. Creationists generally believe 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 brought forth according to their own kind. (Cats bring forth cats, not dogs). By definition, the faith-based Theory of Special Creation is purely a religious concept, acceptable only on the basis of faith. It has no scientific basis.

1. Scientific Evolution

List o' 10 Theories of How Life Began - Evolution

This theory relies strongly on the Big Bang theory of the Creation of the Universe, which was the beginning of the formation of matter. This eventually led to the creation of planets, Pangaea and life on earth as it evolved over millions of years in a natural environment of chemicals and enabling elements. Evolution of life can mean many things. Some use the word to refer to any change at all. Obviously the creation/evolution debate is not about that kind of a definition. Creationists agree that many changes take place, but disagree with the theory of evolution when it is used to mean that a gradual progression from molecules to man produced all living things by natural means, that is, without the involvement of an intelligent Creator.

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