Evolution: Origin of Life and Evidences — Part 1: Origin of life and morphological evidence: visual lesson, ISC Class 12 Biology

Lesson

Origin of life and evidences of evolution

Part 1 — how life may have begun on Earth, and what the bodies of living organisms tell us about their common ancestry.

In this lesson you will

Compare abiogenesis, biogenesis and panspermia
Explain the Oparin–Haldane theory and why a reducing atmosphere was needed
Distinguish protobionts and coacervates, and describe the Miller–Urey experiment
Distinguish homologous, analogous and vestigial organs with examples

Concept

Three old ideas about the origin of life

Early explanations differed on whether life can arise from non-living matter.

Table comparing abiogenesis, biogenesis and panspermia
Idea	Claim	Status
Abiogenesis (spontaneous generation)	Life arises from non-living matter, such as maggots from rotting meat	Disproved for present conditions by Louis Pasteur’s swan-neck flask experiment
Biogenesis	Life arises only from pre-existing life	True for life today
Panspermia (cosmozoic theory)	Spores or units of life came to Earth from outer space	Does not explain how life began in the first place

Concept

The Oparin–Haldane theory

A. I. Oparin (1924) and J. B. S. Haldane (1929) proposed that life arose by chemical evolution in the early Earth’s reducing atmosphere of methane, ammonia, hydrogen and water vapour, with no free oxygen. Energy from lightning, UV radiation and volcanic heat formed simple organic molecules, which collected in the sea as a “hot dilute soup”.

Table of the conditions of the early Earth and why they mattered
Condition	Why it mattered
Reducing atmosphere, no free oxygen	Organic molecules formed were not oxidised or broken down
No ozone layer	Strong UV radiation reached the surface as an energy source
Lightning and volcanic heat	Energy to join simple molecules
Warm seas	Molecules accumulated and reacted further

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