Introduction to origin of life on Earth
The origin of life on earth is one of the great mysteries in the Universe. Scientists are still doing researches to find the origin of life on earth. It is considered the life was originated on earth from the microorganisms. Through this article you can get an idea of how microorganisms evolved to the life origin on earth. The Earth itself is not much older, having formed 4.5 billion years ago. Early Earth was hot, violent, barren, and lifeless. But, 3.5 billion years ago, something happened to Earth to change all that. 1st life formed on Earth. Let’s explore the origin of life.
Living matter and nonliving matter
Living organisms are composed of elements, which are common to the nonliving environment. There can be differences in the composition and ration of elements but living matter and nonliving matter both are composed of common elements; C, H, O, N and some other elements can be seen in larger amounts in living organs. The same elements are available also in the nonliving environment. In living organisms, these elements are organized into molecules, cells, and tissues. Nonliving environment, for example, in soil also there are some organizations, and soil elements are usually organized into molecules.
Organized matter both living and nonliving can show some functions. For example, the computer has a variety of functions. A plant can show some functions different from the computer and most of them are usually more complex than the functions of the computers. Human brain is an example for the structure composed of highly organized matter. What is common to the computer, the plant and the human brain? And three are structures that can show functions. The secret behind the function is nothing but the organization of matter in an order.
If the structure is disturbed or disorganized the function will be lost proportionately to the damage done to the structure. If the structure is damaged to a large extent the function will be lost irreversibly. This is common to both living and nonliving matter.
Origin of living matter on earth
The early earth had no liquid water, because it was too hot. Slowly it was cooled down, until liquid water was formed. There were atmospheric gases except for oxygen gas. Oxygen was available in other forms but not as a gas. There were various forms of energies available. As there was no ozone (O3) layer UV was coming to the earth surface without any barrier. During this time lightning struck happened heavily.
The high energy released from lightnings also contributed to the origin of life. Volcanoes, hot water springs also provided energy. Volcanoes and hot water springs also provide energy. Certain types of clay act as catalysts. Under this energy and catalysts; water, CO2, CO, CH4, H2 and N2 confined to form basic bio molecules. Such as lipids and amino acids. The best possible arrangement for lipids in water is either floating on the top or forming globules.
The scientists, Harold Urey and Stanley Miller performed a landmark experiment to explain this incident. The famous Miller-Urey experiment shows that electric sparks can produce amino acids and some other primary molecules such as monosaccharides in presence of CO2, CO, CH4, H2, N2 and water.
This process took place in larger oceans. This is like a soup and it is called as the Primordial soup. The origin of life from Primordial soup, describes in Heterotrophic theory (Oparin-Haldane hypothesis, Heterotrophic origin of life theory). This theory first introduced by the two bio scientists called Alexander Oparin in 1924, and John Burdon Sanderson Haldane in 1929.
Two layers of lipids arranged in the form of a globule is an arrangement in which the lipid molecules can maintain in which the lipid molecules can maintain the last amount of repulsion between molecules. This arrangement provided ideal conditions for the evolution of this globule into a cell. The lipid bi-layer with embedded proteins provided passage for exchange of matter between the inside of the globule and the outside environment. Its inside was not completely cut off from the outside environment. It was also not completely opened to the environment. This helped the evolution of the structures into a cell. It would keep the changes inside without mixing with the environment.
The membrane remained as one of the most important structures throughout the evolution. Advanced functions such as respiration are associated with the membrane. If oxygen was there, there will be a possibility of burning. So, as there was no oxygen there was no choice for burning.
The origin of Nucleic Acids
Nucleic acids are another important constituent of all living things today. DNA and RNA act as nucleic acids in living cells. There are various hypothesis about how did these two components arise.
RNA formed first. Because RNA can store information like DNA and can act as an enzyme like protein. After evolving the organisms, DNA and proteins took precedence. But how did this RNA come is the next question. Some researchers pointed out that RNA evolved spontaneously.
The RNA word hypothesis published in 2015 made this quite clear. Initially there were only few small molecules which then organized into a simple capsule like structure. This hypothesis suggested that RNA molecules may subsequently evolved to perform more efficient metabolism in the capsule
The origin of Eukaryotic cell
The first cells originated on earth were prokaryotic type of cells. Those cells had the simplest prokaryotic structure and they were called the pre-prokaryotic cells. The present-day prokaryotes and Eukaryotes were evolved from the pre-prokaryotes. Eukaryotic cells were formed by an interaction between two pre-prokaryotic cells. This is described as Endosymbiotic theory of the evolution of Eukaryotes.
This theory describes the origin of Eukaryotic cell as a result of engulfing of one prokaryotic cell by another one. That’s how the Eukaryotic organelles got two membranes of lipid bilayer. There’s an inner membrane which performs the function. For example, respiration occurs in the inner membrane of the mitochondrion. It is similar to the cell membrane of a prokaryotic cell. Respiration occurs in the cell membrane of a prokaryotic cell.
The evidence to show that Eukaryotic cells have a prokaryotic origin.
- Membranes – Mitochondria have their own cell membrane just like a prokaryotic cell does.
- DNA – Each mitochondrion has its own circular DNA genome like a bacteria’s genome, but much smaller. This DNA is passes from a mitochondrion to its offspring and is separated from the host cell’s genome in the nucleus.
- Reproduction – Mitochondria multiply by pinching in half, the same process used by bacteria. Every new mitochondrion must be produced from a parent mitochondrion in this way. If a cell’s mitochondria are removed. It can’t build new ones from scratch.
- rRNA – The seminaries of r-RNA genes of bacteria and organelles like mitochondria and chloroplasts.
- Transport proteins are found in the outer membranes of mitochondria and chloroplast as in prokaryotic cells.
Pasindu Chamikara – Microbiologist