Early Conditions on Earth
Water is essential for all life on Earth and serves the following functions:
- Transport. Water is a solvent in blood and sap so nutrients such as oxygen, CO₂and sugars can be efficiently carried around organisms.
- Temperature control. Water evaporates off the skin, cooling the body when it is too hot. Heat can also be transferred via water around the body.
- Physiological solvent. Most chemical reactions in the body take place dissolved in water. Any substance which in involved in chemical reaction in an organism has a PHYSIOLOGICAL FUNCTION.
- Expands when frozen. Ice floats as it is less dense than water, so it keeps the cold air above the ice separate from the water below it. This keeps the water underneath the ice warmer, preserving life below in colder weather. It also explains why lakes don't freeze all the way to the bottom!
- High SPECIFIC HEAT CAPACITY. This means that water warms up and cools down slowly, which aids temperature homeostasis (internal balance) in organisms.
- Aquatic habitats. Where would we be without the oceans, seas, rivers and lakes??
Most of the planet is above 0°C, so water in organisms does not freeze. Most enzymes need liquid water as a solvent for reactions. In most cases if the temperature were any higher, they would denature and the organism would die. However some organisms can withstand much higher temperatures. They are known as THERMOPHILLIC.
The appropriate mix of gases are needed such as CO₂for photosynthesis, oxygen for respiration and nitrogen for protein synthesis.
Light and solar radiation
Sunlight provides energy for photosynthesis.
Heat is produced when water is absorbed. This is the energy source in the water cycle.
Low levels of harmful UV radiation.
Distance from the sun controls light levels and temperatures.
Rotation of Earth controls day and night and therefore temperatures.
Tilted axis causes seasonal variation in tempertaure.
Earth's magnetic field deflects harmful solar radiation.