Science - Fossils


  • A fossil is evidence of past life.
  • Fossils can be part of an organism, such as its bones, teeth, feathers, scales, branches or leaves.
  • Fossils can also be traces, such as footprints, burrows and other evidence that an organism existed in an area.
  • Fossils provide evidence that life has changed over time. Some life forms that used to exist on Earth no longer exist.
  • Studying the fossil record also provides evidence that life forms have become more complex over time.
  • The study of fossils is called Palaeontology.

Major Milestones in the history of life

  • Ice Ages
  • Cambrian Explosion
  • Photosynthesis
  • Merger between mitochondria and anaerobic organisms
  • Formation of the KT Boundary (Extinction of the dinosaurs)
  • Motion of tectonic plates
  • Land animals developing eggs
  • Animals moving onto Land

Formation of life on Earth

  1. Planet Earth forms
  2. Core and Crust forms
  3. First Oceans
  4. First Life (Cyanobacteria or Archea)
  5. Oxygen accumulates in the atmosphere
  6. First Animals
  7. First Vertebrates (Fish)
  8. First land plants
  9. Dinosaurs
  10. Dinosaurs go Extinct
  11. Humans

Theory of evolution

  • All life on Earth shares a common ancestor.
  • All the different species on Earth underwent mutations in the past to better suit their environment.
  • Evolution (Not Theory of Evolution) means “descent with modification”

Natural Selection

  • Natural selection is the concept of survival of the fittest.
  • There are 4 conditions for natural selections: variation between individuals, heredity, reproduction and variation of fitness
  • Selective pressures are phenomena that impact on an organism’s fitness

Stages of Natural Selection

1. Isolation

  • A species becomes separated by an environmental factor e.g. formation of a river

2. Variation

  • A mutation occurs in one of the isolated groups

3. Selection

  • If the mutation improves fitness, the mutation is passed on to the next generation

4. Speciation

  • After several generations, the isolated group has a majority of individuals carrying the mutation, and these individuals are considered to have evolved.

Law of Superposition

  • Because upper layers are younger than the ones beneath them, the law of superposition states that a fossil’s age can be determined by the age of fossils around them. This only applies to UNDISTURBED rock.
  • Relative age: age of the fossil based on the Law of Superposition, e.g. Fossil A is older than Fossil B but younger than fossil C.
  • Absolute age: the actual age of the fossil, e.g. Fossil A is 6000 years old.

Analysing the Fossil record

  • Faulting can cause projections of rock through other layers.
  • Folding results in layers of rock being moved away from each other.

Why are fossils important?

  • Fossils allow us to determine early biodiversity
  • Fossils can be compared to modern day organisms
  • Fossils improve our understanding of previous conditions on Earth
  • Fossils support our estimates for the age of the Earth
  • Fossils provide evidence for Evolution
  • Fossils provide evidence of continental drift

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Pranav Sharma
Pranav Sharma
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UNSW Student, site owner and developer.