Evolution

Lesson

Part 1 — how life may have begun on a young Earth, and the evidence that living things have changed over time.

In this lesson you will

Outline the main ideas about the origin of life, including chemical evolution
Describe Miller’s experiment and what it showed
Explain palaeontological, anatomical, molecular and embryological evidence for evolution
Explain industrial melanism and resistance as evidence of natural selection

Concept

A timeline of beginnings

The universe is very old — about 20 billion years, according to the textbook account of the Big Bang. The Earth formed about 4.5 billion years ago; life appeared about 4 billion years ago.

Table of approximate times of the origin of the universe, Earth and life
Event	Approximate time ago
Big Bang: the universe begins	About 20 billion years
Earth forms	About 4.5 billion years
Life appears	About 4 billion years
First non-cellular forms of life	About 3 billion years
First cellular forms	About 2000 million years

Concept

Early ideas about the origin of life

Several ideas were proposed; experiments ruled some of them out.

Table of four ideas about the origin of life with claims and status
Idea	Claim	Status
Special creation	All living beings were created as they are, a few thousand years ago	Not supported by evidence
Spontaneous generation	Life arises from decaying and rotting matter, such as straw or mud	Disproved by Louis Pasteur
Panspermia	Units of life (spores) came from outer space	Speculative
Chemical evolution (Oparin and Haldane)	Life arose from non-living organic molecules	Supported by experiments

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