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Evolution is one of the Biology Topics that has been debated and studied for centuries, exploring the process by which species change over time.
How Life Originated on Earth? – The Conditions that Sparked Life on Earth
It was the ancient belief that the earth is unalterable which means that the size and shape of the earth at the initial stage of its formation has remained static upto the present stage. The living world also has remained in its static fashion and there is no difference between the ancient life forms and the present picture of the living world. During 5000 BC, a scientist named Xenophane first discovered several fossils and he gave a blow to the false ideas on the configuration of the earth. He proved that there have been significant changes in the living world from ancient times to recent times. The fossils discovered by him were supportive of his ideas.
At 400 BC, the great philosopher Aristotle proved that in the living world, there are many classes of organisms and one class may be more highly organized than the other class. The organisms have evolved from some ancestors through modification in time and space. This is called evolution. The term ‘Evolution’ originated from the Latin word “evolvere”, which means “to unfold or unroll.” Biological evolution refers to the “Change in the properties of groups of organisms throughout a generation.” The term evolution was first used by Albrecht Von Haller. The branch of biology that deals with the evolution of organisms is known as Evolutionary Biology. Scottish Geologist Charles Lyell in 1982 in the discussion related to species used the term ‘evolution’. In life science this is the modern use of the term evolution. Therefore, evolution may be stated as a slow and dynamic process that promotes the development of organisms with higher and more complex organization from the simpler pre-existing form of organization.
According to Herber Spencer, an English educationist, evolution refers to the slow, dynamic, and phasic modification of living entities of simpler organization to produce forms of complex organization. Charles Darwin considered evolution as Descent with Modification.
Evolution may be defined as the alteration in the genetic composition of a population from the pre-existing life forms over a successive generation.
Origin of Universe
- The vast universe is comprised of huge clusters of galaxies that originated about 20 billion years ago.
- The Big Bang theory attempts to explain the origin of the universe.
- According to this theory, a singular, unimaginable large explosion created the universe.
- Present-day galaxies were formed, as the universe expanded and cooled, temperature of the space came down and materials were condensed under the influence of gravitation.
- Milky Way, our galaxy was supposed to have been formed 4.5 billion years back approximately.
- Early Earth was devoid of atmosphere. Earth’s surface was covered by water vapour, methane (CH4), ammonia (NH3), and carbon dioxide (CO2) from the molten mass.
- Water was broken by the action of UV rays from the Sun and formed oxygen and hydrogen.
- H2O, CO2, and other gases were formed by the combination of oxygen with ammonia and methane.
- Ozone (O3) is also formed from oxygen, the ozone layer acts as a shield to protect our present atmosphere from harmful UV rays.
- Life appeared about 4 billion years ago now, i.e. 500 million after the formation of Earth.
Concept About Origin of Life
Among much inquisitiveness, the questions on the origin of life appear prominent. Though Earth originated about 4.6 billion years ago, the origin of first life is a later event. However, at what time and how life originated, is not known to us. Based on several observations and primitive records on the earth’s crust we may predict something about the origin of life. It is presumed that after the origin of Earth, it took about one billion years to give the origin of blue-green algae. Primitive philosophic ideas state that the higher group of animals including man appeared by the grace of God, while the creatures like insects, frogs, reptiles, etc. developed spontaneously.
Famous scientist, Louis Pasteur first put an objection to the spontaneous origin of life. With the help of some experiments, he could be able to prove that by no means life could be originated spontaneously. Those who believe in the spontaneous creation of life present some simple observations. For example, if some food is left uncovered outside, it develops maggots in the food, and from the maggots flies appear in the long run. Besides, sometimes it is noticed that rats appear in dirty form clothes left in the corners of the rooms.
There is no scientific evidence to support these ideas. Spallanzani Francesco Redi, one scientist from Italy objected the spontaneous origin of life. Redi’s conception was based on some experimental observation. So also was the observation of Spallanzani based on some experimental findings. Therefore, the experiments of Redi and Spallanzani may be discussed.
How Life Originated on Earth?
Life is defined as “the ability of an organism to reproduce, grow, and produce energy through chemical reactions to utilize the outside materials.”
Theory of Abiogenesis:
According to the theory of Abiogenesis (Abio – non-biological, genesis – formation), life originated from non-living matter; that means complex living organisms originated from decaying organic substances. It is also known as the spontaneous theory of the origin of life. e.g. maggots appeared spontaneously in meat.
Theory of Biogenesis:
Theory of Biogenesis states, living things no matter has small only appears from pre-existing life.
Difference between the theory of abiogenesis and the theory of biogenesis:
| Theory of Abiogenesis | Theory of Biogenesis |
| 1. Life originates from inert non-living matters. | 1. A life can only produce another life. |
| 2. There is no experimental evidence. | 2. Supported by experimental evidence. |
| 3. Maggots from decomposed meat, form dirty hosts giving the origin of rats and frogs during the rainy season are given as examples of this idea. | 3. Uninfected food, and protected clean clothes cannot show the appearance of rats. |
| 4. It supports spontaneous creation. | 4. It does not support spontaneous creation. |
| 5. This idea is based on religious belief. | 5. This idea is based on logic and scientific investigations. |
Theories of Origin of Life
Various theories have been put forward to explain the origin of life.
1. Theory of Special Creation:
According to this theory (Suarez 1548-1617), every life form was created by a supernatural power as a separate and fixed entity without changing itself all of a sudden.
2. Theory of Spontaneous Generation:
This theory states that various types of living organisms originated spontaneously from non-living substances automatically over time. Anaximander (611-547 BC) and Aristotle (384-322 BC) were the main propounders of this theory.
3. Cosmozoic Theory or Theory of Cosmic Origin:
This theory was proposed by Ritcher (1865). According to this theory, protoplasm reached the earth in the form of spores or germs from some unknown part of the universe with the cosmic dust and subsequently evolved into various forms of life. This theory is also known as the ’Theory of Panspermia’.
Drawbacks of the Theory of Cosmic Origin:
- Absence of life forms on any planet except Earth.
- No details about the spores, their origin, and their mechanisms of crossing interplanetary space and reaching Earth.
- No scientific experiments were given to support the theory.
4. Theory of Catastrophism:
According to this theory, life is originated by the creation and it is followed by catastrophe (Calamities) due to geographical disturbances.
5. Theory of Oparin and Haldane in Favour of Origin of Life:
In 1920 Alexander I. Oparin suggested that under the influence of solar radiation, thunderstorms, volcanic eruptions, heat due to radiation, UV radiation, cosmic rays, etc. The gaseous elements in the primitive environment of the earth reacted to produce small organic molecules. Simple small organic molecules on polymerization produce large molecules in the way of origin of living form. In the subsequent period, J.B.S. Haldane in 1928 proposed a similar idea on the origin of life. This concept of the origin of life given by both scientists is known as Naturalistic Theory or Chemosynthetic Theory. The theory suggests that before the origin of life, organic molecules were formed. The mechanism by which the simple inorganic components produce simple or complex organic compounds is known as chemical evolution.
According to Haldane in the primitive environment of the earth, the organic compounds got mixed with seawater to produce a solution favourable for the formation of life. Haldane called this mixture Hot Dilute Soup. To explain the mechanism of the formation of primary life from common organic compounds, Oparin suggested Coacervate Model. According to him, the coacervate was a complex of lipids, carbohydrates, and proteins. This was spherical and with two coverings. He also stated that the coacervate could increase in size by accumulating lipids from the environment and they could multiply producing buds. Oparin opined that coacervate was the first cellular organism.