Tuesday, September 26, 2017

CBSE Class 10 - Biology - Heredity and Evolution - Origin Of Life On Earth (Concept Points) (#cbseNotes)

Origin Of Life On Earth (Concept Points)

CBSE Class 10 - Biology - Heredity and Evolution - Origin Of Life On Earth (Concept Points) (#cbseNotes)

Most scientists believed that life arose from nonliving matter, mostly from gases. It originated in primitive form in the oceans of the earth.

4 billion years ago, the primitive atmosphere was formed. It had little oxygen and was likely thick with water vapor, along with compounds released by volcanic eruptions, such as nitrogen oxides, carbon dioxide, methane, ammonia, and hydrogen.

As the Earth cooled, the water vapor condensed into oceans, and much of the hydrogen escaped into space.

Two scientists, Alexander Oparin and J. B. S. Haldane, proposed that the primitive atmosphere contained the following gases: methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water (H₂O). These gases collided which led to the formation of simpler organic molecules.

Stanley L. Miller and Harold C. Urey, in 1953 conducted an experiment. They simulated the conditions of primitive Earth in a laboratory. They assembled an atmosphere similar to that thought to exist on early earth (this had molecules like ammonia, methane and hydrogen sulphide, but no oxygen) over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules

In 2008, scientists used modern equipment to repeat Miller and Urey experiment. They concluded that numerous amino acids had formed under conditions that simulated a volcanic eruption.

It is believed that the first genetic material was most likely RNA, not DNA. This is called the RNA-world hypothesis. Unlike DNA, RNA can take many forms. It is possible that RNA molecules capable of replicating form the first life forms.

Cynaobacteria are considered to the first autotrophs that are responsible for filling up Earth’s atmosphere with oxygen. This is called the Great Oxygenation Event. (See link)

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