planet earth as a self-regulating system (within some limits)

The Gaia hypothesis

All organisms and their inorganic surroundings on Earth are closely integrated to form a single and self-regulating complex system, maintaining the conditions for life on the planet

Key ideas

• Organisms coevolve with the environment

• Planet earth sometimes linked to a single living organism

• The planet stays within a narrow window of conditions suitable for life due to feedbacks within the system

geosphere (lithosphere)

earth’s interior or solid earth, rocks and soils

Earths systems

geosphere, atmosphere, hydrosphere and life (biosphere)

hydrosphere

water and water locked up as ice (cryosphere)

life (biosphere)

plants, animals, fungi, archaea, bacteria

earliest evidence of life on earth

3.5 Ga in the form of fossilised photosynthetic stromatolites

examples of geosphere interactions with other reservoirs

• Volcanic eruptions add CO2 to the oceans and atmosphere

• Degassing of Earth's interior affects the Earth's atmosphere

• Chemical weathering of rocks removes the CO2 from the atmosphere

• New basaltic rock reacts with seawater at mid-ocean ridges

divergent

plates boundaries moving apart

convergent

plates moving towards each other

earth’s cycles

formation of new oceanic crust at divergent plate boundaries where 2 plates are pulling apart

submarine volcano CO2 discharge

remains unmeasured

water and the geosphere

Seawater interacts with new holt basaltic rock near the mid-ocean ridges, altering the composition and the rock (basalt)

composition of seawater

strongly influenced by this interaction between the hydrosphere and geosphere

residence time

the average amount of time that a particle spends in a particular system

summer CO2

photosynthesis peaks in summer - drawing down CO2

winter CO2

decay of plant releases CO2 and anthropogenic CO2 emissions are also highest in winter

ocean

As the ocean continues to absorb CO2, however, the rate at which it does so is expected to decrease because of the changes in its carbonate chemistry. Eventually the ocean will not be able to absorb more CO2

positive feedbacks

reinforce an initial change or forcing

negative feedbacks

reduce, counteract or dampen an initial change or forcing

example of a positive effect

the albedo effect

example of a negative effect

chemical weathering

chemical weathering acts as a

global thermostat

why has the Gaia hypothesis been debated

Some of the more extreme/literal interpretations have been largely discredited (e.g. no sentience/purpose involved). It is undeniable that organisms have altered their environment.

Many negative feedbacks (although not just involving life) have been identified within the

Earth System which have kept conditions within a habitable range