B3 Life on Earth

How did life on Earth begin and evolve?

  • The many different species of living things on Earth (and many species that are now extinct) evolved from very simple living things.
  • Life on Earth began about 3500 million years ago.
  • Evidence for evolution is provided by fossils and from analysis of similarities and differences in DNA of organisms.
  • The first living things developed from molecules that could copy themselves.
  • These molecules were produced by the conditions on Earth at that time, or may have come from elsewhere.
  • Evolution happens due to natural selection.
  • The process of natural selection involves variation, competition, increased chance of survival and reproduction, and increased number of individuals with certain characteristics in later generations.
  • Both environment and genes cause variation, but only genetic variation can be passed on.
  • The difference between natural selection and selective breeding is that people have carried out selective breeding with the aim of improving a species.
  • Changes can occur in genes, they are called mutations.
  • Mutated genes in sex cells can be passed on to offspring and may occasionally produce new characteristics.
  • The combined effect of mutations, environmental changes and natural selection can produce new species.
  • If the conditions on Earth had, at any stage, been different, evolution by natural selection could have produced different results.
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