Early Life on Earth

How conditions allowed early life to develop and survive on Earth

Atmosphere

The Earth's atmosphere is created by its mass, which is great enough to prevent most gases from escaping into space.

This included the essential elements for life:

  1. Carbon
  2. Hydrogen
  3. Oxygen
  4. Nitrogen

Which were present in compounds like:

  1. Methane
  2. Ammonia
  3. Carbon Dioxide

The atmospheric pressure was high enough to prevent all the liquid water from boiling.

Why is water important?
  • The general physiological solvent in which most biological reactions take place
  • Important in transport and temperature regulation

Insolation

  • Sunlight provides energy for photosynthesis
  • Heat absorbed by the absorption of sunlight provides the energy that:
    • Drives the water cycle
    • Warms the Earth's surface and oceans
  • Albedo of the surface changes the amount of sunlight that is absorbed
  • Composition of the atmosphere controls the amount of infrared energy that is absorbed and converted to heat

Position in the solar system

  • The Earth is the perfect distance from the Sun
    • If it were closer or too far away, there wouldn't be liquid water
  • The time taken for Earth to rotate on its axis also produced a day/night cycle that was fast enough to minimise excessive heating or cooling

Orbital behaviour

  • The axis of Earth's rotation is at an angle to its orbit around the Sun, producing seasonal variations in conditions
  • The 24 hour period of rotation of Earth around its axis reduces temperature extremes as the Earth orbits the Sun

Magnetosphere

  • Molten layers beneath the Earth's crust produce a magnetic field
  • This magnetic field deflects 'solar wind', preventing biologically damaging radiation from reaching the Earth's surface

How the presence of life has brought about environmental change

Atmospheric oxygen

  1. Archaea in the oceans developed the ability to photosynthesise, releasing oxygen
  2. Initially, all the produced oxygen reacted with iron in the oceans
  3. Then, after all the iron had reacted with oxygen, the surplus built up in the oceans, much of which was released into the atmosphere

Carbon sequestration

  • Carbon dioxide helps to retain heat energy in the atmosphere as it is a greenhouse gas
  • Photoautotrophs (photosynthetic organisms) absorbed carbon dioxide, some of which was stored in geological sediments like fossil fuels and carbonate rocks.
  • The removal of atmospheric carbon dioxide helped to prevent long-term temperature increases, as the Sun's intensity increases every billion years.

Biogeochemical cycles

  • As more organisms evolved, interconnected biological processes developed, producing biogeochemical cycles
  • These meant that relatively small amounts of some nutrient elements could support life over long periods of time without resources becoming depleted.

Transpiration

  • Once plants had evolved, colonising land, transpiration returned water vapour to the atmosphere, increasing the amount of rainfall in other areas
  • This made the growth of even more plant life possible.

How past conditions on Earth were monitored and how these methods have developed

  • Radioisotope composition can be used to date samples, like the ratio of carbon-12 to carbon-14
  • Ratio of oxygen-18 to oxygen-16 can be used to estimate past temperatures
  • Composition of past atmosphere can be analysed from air bubbles collected from ice cores
  • Ratio of magnesium to calcium in calcite deposits can be used to estimate the temperature, as more magnesium is incorporated at higher temperatures