Class 12 Biology Chapter 6
Evolution
Important Questions

Explanation:
The origin of life on Earth is a fundamental question in biology. The widely accepted hypothesis is that life originated through a gradual chemical evolution of non-living organic molecules.

• Primordial Soup Theory: This theory suggests that life began in a "primordial soup" of organic molecules, in the early oceans of Earth, under a reducing atmosphere.
• Miller-Urey Experiment: In 1953, Stanley Miller and Harold Urey conducted an experiment to test this hypothesis. They created a closed environment simulating the Earth's early atmosphere, which they believed was rich in methane, ammonia, hydrogen, and water vapour. They exposed this mixture to electric sparks to mimic lightning, a common occurrence on early Earth. After a week, they found that several organic compounds, including amino acids (the building blocks of proteins), had formed spontaneously.
• Significance: The Miller-Urey experiment provided the first evidence that organic molecules necessary for life could be synthesised from inorganic precursors under conditions thought to resemble those of early Earth. It suggested a possible pathway for the chemical evolution of life.
• Further Developments: Since then, further research has proposed that life's building blocks could also have originated in other environments, such as hydrothermal vents on the ocean floor. The exact process of how these molecules formed the first living cells remains a topic of research and debate, illustrating the complexity of life's origins.

This experiment and subsequent research into the origin of life highlights the significance of chemical processes in the early Earth environment in the development of life.