Origin Of Life On Earth: Theories, Formation And Evolution

The origin of life study is important to biological sciences as it unravels the basic processes that led to the origin of living organisms. Biologically, life is, for instance, identified with metabolism, growth, and reproduction. This helps in understanding the complexities of living systems and the history of biological evolution.

Formation Of The Earth

The Formation of the Earth began about (4.5 billion years ago):

Initial Earth Conditions

It is thought that the Earth must have existed as a molten body with extremely high temperatures for nearly 4.5 billion years. There was no solid crust or atmosphere as we experience it today, and thus the early Earth was not a place in any event.

The Cooling Process

As the Earth started to cool down, it started forming a solid crust that led to the condensation of the water vapour into liquid water. This process later led to the formation of the Earth's oceans and eventually formed its early atmosphere.

Primitive Atmosphere Composition

The early atmosphere is composed mainly of methane (CH4), ammonia (NH3), water vapour (H2O), and hydrogen (H2). Free oxygen (O2) was not yet part of the atmosphere, even though this gas was to become the biggest component of the later atmosphere.

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• Mutation - a genetic change

• Difference between Spontaneous and Induced Mutation

• Gene Flow and Factors affecting

• Natural Selection

Origin Of Life Theories

Origin of Life Theory of Spontaneous Generation goes as follows:

The theory of spontaneous generation stated that life would originate spontaneously from inorganic matter, such as rotting organic matter. The theory became quite popular until experiments carried out in the 17th and 18th centuries proved it incorrect.

Biogenesis

• Biogenesis is the concept of the origin of life through existing life-forms.

• The concept of biogenesis replaced the theory of spontaneous generation.

• This concept has formed the basis of present-day biology to affirm that life can not come from any material dead under natural conditions.

Oparin-Haldane Hypothesis (Chemical Evolution)

• Alexander Oparin and John Haldane proposed in the 1920 that life came about through chemical evolution.

• Such scientists thought that the simple organic molecules were created from the inorganic compounds in Earth's early oceans using the energy from sunlight and lightning and primordial soup.

Miller-Urey Experiment

• In 1953 Stanley Miller and Harold Urey simulated what might be considered early Earth conditions in an experiment.

• They showed that organic compounds, including amino acids, might be produced from simple gases (methane, ammonia, hydrogen) under conditions taken to approximate those of the early Earth.

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Steps Of Chemical Evolution

The steps of chemical evolution are as follows:

Atomic Stage

Some of the most important elements for life include carbon, hydrogen, oxygen, and nitrogen. With decreasing temperature, Earth started producing those essential ingredients. The three earliest species included water's molecules H2O, ammonia NH3, and methane CH4 .

Formation Of Basic Organic Molecules

Simple organic compounds were formed as a result of the interactions between atmospheric gases and sources of energy, like UV radiation and electrical discharges. These involved all such things like amino acids, sugars, and fatty acids-the basic ingredients of life.

Formation Of Complex Organic Molecules

The simple organic compounds polymerized to create larger and more complex molecules. Thus, the amino acids were linked together to form proteins, sugars into polysaccharides, and fatty acids to lipids.

Formation Of Coacervates

Coacervates are colloidal droplets made up of complex organic molecules. These protocells displayed properties of living cells, for example, the ability to concentrate as well as segregate organic molecules that formed a basis for creating the first true-living cells.

First Life Forms

First life forms are said to be:

Protobionts (First Cells)

• Protobionts were the first cell-like structures with some rudimentary metabolic functions but lacked complex genetic machinery.

• They were a transitional form from simple molecules to more complex living forms.

Anaerobic Heterotrophs

The first forms of life were anaerobic heterotrophs, which do not require oxygen and which primarily acquire energy and nutrients in the form of organic compounds from their surroundings. They survived well in an oxygenless environment.

Photosynthetic Organisms

The evolution of photoautotrophic organisms that harboured the energy from sunlight in the form of chemical energy and discharged oxygen as a by-product was another crucial milestone. This process started to increasingly fill the atmosphere with oxygen, thus paving the way for aerobic forms of life.

Transition To Biological Evolution

The emergence of biological evolution is attributed to the:

Origin Of DNA / RNA

The rise of nucleic acids like DNA and RNA was a very crucial mutation in evolution. These molecules carried genetic information and had a command over the development of more complex forms of life through genetic control and replication.

Natural Selection And The Evolution Of Complex Life

Charles Darwin's process of natural selection is that whereby diversification and evolution of complex life forms took place. Over time, from simpler original organisms, they gradually adapted themselves to more complex and diversified species through adaptation and survival mechanisms.