Origin of Life on Earth: Best Biology Notes

The origin of life on Earth has been a topic of fascination and intrigue for millennia. As we gaze up at the stars and wonder about the vastness of the universe, it is equally captivating to ponder how life, as we know it, came into existence on our pale blue dot. Though the exact process that led to life’s inception remains shrouded in mystery, scientists have made remarkable strides in understanding the various theories and mechanisms that may have played a role in the genesis of life on our planet.

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origin of life

The Origin of Life

Life evolved on planet Earth about 3.5 billion years ago. Since then, approximately 15 million different species of organisms have evolved.  But only about two million have been identified so far. We will learn how the life of these, at first originated on earth and how such a vast variety of organisms evolved.

Here, we have to understand the difference between the Origin of life and the Evolution of Life. The origin of life means the appearance of the simplest primordial life from non-living matter. Whereas, The evolution of life means the gradual formation of complex organisms from simpler ones.

Several theories have been put forth to explain the origin of life. but the most appropriate theory is the Chemosynthetic Theory of the Origin of Life.

Also Read: Plant Parts | Human Health & disease | Important Biological Terms | Viruse & Bacteria

Chemosynthetic Theory of Origin of Life

  • This theory is widely accepted for the origin of life.
  • It was proposed by A. I Oparin.
  • Life might have originated at first on Earth through a series of combinations of chemical substances in the distant past and it all happened in water.

Explanation of Chemosynthetic Theory for Origin of Life

  • The earth originated about 5 billion years ago.
  • It was initially made up of hot gases and vapours of various chemicals.
  • Gradually it cooled down and a solid crust was formed.
  • The early atmosphere contained ammonia (NH3), water vapour (H2O), hydrogen (H2), and Methane (CH4). At that time there was no free oxygen. This sort of atmosphere (with methane, ammonia and hydrogen) is still found on Jupiter and Saturn.
  • Heavy rains fell on the hot surface of the earth, and over a very very long period, the water bodies appeared that still contained hot water.
  • Methane and ammonia from the atmosphere dissolved in the water of the seas.
  • In this water, chemical reactions occurred and gave rise to amino acids, nitrogenous bases, sugars and fatty acids which further reacted and combined to give rise to biomolecules of life such as proteins and nucleic acids.

Probable Stages in the Origin of Life:

First Stage:

UV rays or electric discharge (lightning) or heat were the sources of energy when the earth formed. Either alone or a combination of these energy sources caused reactions that produced complex organic compounds (including amino acids) from a mixture of ammonia (NH3), methane (CH4), water (H2O) and Hydrogen (H2). The amino acids are the building blocks of proteins which are the main components of protoplasm.

Stanley Miller and Harold C Urey Experiment: In 1953, Stanley Miller and Harold C. Urey set up an experiment with an air-tight apparatus in which four gases (NH4, CH4, H2 and H2O) were subjected to an electric discharge for one week. On analyzing the liquid, they found a variety of organic substances in it, such as amino acids, urea, acetic acid, and lactic acid.

Second Stage:

Simple organic molecules combined to form large molecules which included peptides (leading to the formation of proteins), sugars, starch and fat molecules.

Third stage:

The large molecules of different kinds combined together to form multi-molecular heaps or complexes. Some simple fat molecules arranged themselves around this molecular complex in a sort of membrane. It was observed in the laboratory experiments that when such complexes reached a certain size they separated from the surrounding solution in the form of what were termed “coacervate drops” of microscopic size, moving in the liquid with a definite boundary.

Now, some sort of ‘metabolism’ could occur within these coacervates with the synthesis of certain substances and the breakdown of others. The latter (i.e. breakdown reactions could provide energy.

Some of the earliest-formed proteins might have acted like enzymes and would have affected the rates of reactions. It is also believed that RNA molecules might have shown enzymatic activity in the “Primordial soup” of Chemical compounds.  Such molecules have been termed ribozymes.

Fourth Stage

Some sort of nucleoproteins or nucleic acids may have evolved by random combinations which have provided two more properties to coacervate-like bodies. These include:

  1. Chemical reactions from the nucleic acids and
  2. The capacity to reproduce through duplication of the nucleic acids.

Thus, cells were produced that could be called the simplest primordial life. 

The primitive “drop”-like forms of life were all heterotrophs, unable to manufacture their own food but derived it from the environment.

FAQs on Origin of Life

Q: What is the origin of life?

A: The origin of life refers to the scientific question of how life first arose on Earth. It is the study of how non-living matter eventually led to the formation of living organisms.

Q: How did the first living organisms emerge through abiogenesis?

A: The exact process of how the first living organisms emerged through abiogenesis is not yet fully understood. It is thought to have occurred in several stages. The initial stage likely involved the synthesis of simple organic molecules, such as amino acids and nucleotides, from inorganic compounds. These molecules then combined to form more complex structures, such as proteins and nucleic acids.
Over time, these molecules may have self-assembled into protocells, which were primitive, membrane-like structures with the ability to perform basic functions like metabolism and reproduction. Through a process of natural selection, some of these protocells may have become more stable and capable of further development, eventually leading to the first living organisms.

Q: What were the conditions on early Earth that could have supported the origin of life?

A: Early Earth provided a range of conditions that could have supported the origin of life. Some of these conditions included:
1. Presence of organic molecules: Organic molecules, such as amino acids, were likely formed through chemical reactions in the early Earth’s atmosphere and oceans.
2. Reducing atmosphere: The early atmosphere was likely reducing, meaning it had low oxygen levels, which would have been more conducive to the formation of organic compounds.
3. Volcanic activity: Volcanic activity would have released various gases and minerals that could have contributed to the synthesis of organic molecules.
4. Liquid water: The presence of liquid water on Earth’s surface was essential for the chemical reactions necessary for life to occur.
5. Energy sources: Lightning, UV radiation, and volcanic heat could have provided the energy needed to drive chemical reactions that led to the formation of complex molecules.

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Last updated: August 8, 2023 Updated on 6:42 AM