Aldrin, Armstrong and Collins, Apollo 11’s brave astronauts were the first humans with the privilege of viewing Earth from another celestial body. These men uniquely wondered “what makes Earth special?” Certainly, within our Solar System, planet Earth is very special. Its environment has permitted the evolution of a panoply of life.
Green plants containing the pigment, chlorophyll either in the oceans as algae or on land as a multitude of trees, shrubs and herbs harvest energy from sunshine. Using a series of chemical reactions, known as photosynthesis, light energy is harvested and attached onto compounds containing phosphorus.
Captured energy then drives a series of reactions in which atmospheric carbon dioxide and water are combined forming simple sugars while releasing oxygen. These sugars are used further by plants in the manufacture of larger carbohydrates, amino acids and proteins, oils and fats.
The release of oxygen during photosynthesis forms the basis of life’s second vital process, respiration. Almost all plants and animals utilise oxygen in this energy releasing process during which sugars are broken down.
Released energy then drives all subsequent growth, development and reproduction. These body-building processes in plants are reliant on the transfer of the products of photosynthesis from a point of manufacture, the source, to the place of use, a sink.
Leaves and shoots are the principle sources of energy harvesting while flowers and fruits are major sinks with high levels of respiration.
Figure 1: Photosynthesis vs respiration, drawn by James Hadley
Transfer between sources and sinks occurs in a central system of pipes, the vascular system, using water as the carrier. Water is obtained by land plants from the soils in which they grow. Without water there would be no transfer and subsequent growth. Earth’s environment is built around a ‘water-cycle’ supplying the land and oceans with rain or snow and recycles water back into the atmosphere in a sustainable manner.
Early in Earth’s evolution, very primitive marine organisms initiated photosynthetic processes, capturing sunlight’s energy. As a result, in our atmosphere oxygen became a major component. That encouraged the development of the vast array of land plants which utilise rain water as the key element in their transport systems.
Subsequently, plants formed the diets of all animals either by direct consumption as herbivores or at second-hand as carnivores. As a result, evolution produced balanced ecosystems and humanity has inherited what those astronauts saw, “the Green Planet”.
Earth will only retain this status if humanity individually and collectively defeats our biggest challenge – climate change. Burning rain forests in South America, Africa and Arctic tundra will disbalance these ecosystems and quicken climate change.