The origin of the Earth, Evolution of Earth and life

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The origin of the Earth

Introduction :

The Universe is all of space, time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire Universe is still unknown, it is possible to measure the observable universe.

Lets look at some theories on how the universe originated :

Early Theories

Nebular Hypothesis(1755)

  • The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System
  • There is evidence that Emanuel Swedenborg first proposed parts of the nebular hypothesis in 1734.
  • Immanuel Kant, familiar with Swedenborg’s work, developed the theory further in 1755, publishing his own Universal Natural History and Theory of the Heavens, wherein he argued that gaseous clouds (nebulae) slowly rotate, gradually collapse and flatten due to gravity, eventually forming stars and planets.

Binary theories

  • As per these theories, the sun had a companion.

Revised Nebular Hypothesis

  • Revised Nebular Hypothesis was propounded by Carl Weizascar in Germany and Otto Schmidt in Russia.
  • They regarded that a solar nebula surrounded the sun and that the nebula comprised of chiefly hydrogen, helium and something called dust.
  • The collision of particles and the friction caused a disk-shaped cloud to be formed and then the planets were created via the accretion process.

Modern theories

Big Bang Theory

  • Alternatively called the expanding universe hypothesis.
  • As per this theory, in the beginning, all matter or substance forming this universe existed at one place as a tiny ball. This tiny ball had an extremely small volume, infinite density and temperature.
  • At the Big Bang, this ball blasted fiercely and forcefully and started a substantial process of expansion which continues to this day.
  • Now it is accepted that this event took place approx. 002E 13.7 billion years ago.

Origin of Life on Earth

  • The universe is very old – almost 13 billion years old. Huge clusters of galaxies comprise the universe.
  • The Big Bang theory attempts to explain to us the origin of universe. It talks of a singular huge explosion unimaginable in physical terms.
  • The universe expanded and hence, the temperature came down. Hydrogen and Helium formed sometime later.
  • The gases condensed under gravitation and formed the galaxies of the present day universe.
  • In the solar system of the Milky Way galaxy, earth was supposed to have been formed about 5 billion years back.
  • There was no atmosphere on early earth. Methane, carbon dioxide and ammonia released from molten mass covered the surface.
  • The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, CO2 and others.
  • The ozone layer was formed. As earth cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
  • Life appeared 500 million years after the formation of earth, i.e., almost four billion years back. Some scientists believe that the life came from outer space.
  • The first non-cellular forms of life could have originated 3 billion years back. They would have been giant molecules (RNA, Protein, Polysaccharides, etc.). These capsules reproduced their molecules perhaps.
  • The first cellular form of life did not possibly originate till about 2000 million years ago. These were probably single-cells. All life forms were in water environment only.
  • However, once formed, how the first cellular forms of life could have evolved into the complex biodiversity of today is the fascinating story

Evolution of Life on Earth

  • Evolutionary Biology is the study of history of life forms on earth.
  • Homology indicates common ancestry. In the context of biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different species.
  • A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates.
  • Homology is based on divergent evolution whereas Analogy refers to a situation exactly opposite [convergent evolution].
  • Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions.
  • Hence, analogous structures are a result of convergent evolution – different structures evolving for the same function and hence having similarity.
  • Other examples of analogy are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins.
  • One can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function: Sweet potato (root modification) and potato (stem modification) is another example for analogy.

Adaptive Radiation

  • During his journey, Charles Darwin went to Galapagos Islands. There he observed an amazing diversity of creatures.
  • Of particular interest, small black birds later called Darwin’s Finches amazed him.
  • He realized that there were many varieties of finches in the same island. All the varieties, he speculated, evolved on the island itself.
  • From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches. This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.

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