Ok, so here’s the bottom biological line currently running on the planet Earth. There are these miracle molecules called chlorophyll, which are present in all green plants. They trap photons, particles of energy streaming from the sun and use this light energy to convert water and Carbon dioxide into a C6H12O6, which we all know as glucose – a kind of sugar. Given off from this chemical reaction is some water and Oxygen, which is released into the atmosphere.
The first living things to photosynthesize 3 1/2 billion years ago were blue green algae. The ancient atmosphere of the earth did not have an Ozone layer. This protective shield as you know keeps the extremely damaging ultraviolet light from penetrating down to the surface. UV radiation causes mutations in DNA replication and is very harmful to all living organisms. When these first green plants began emitting oxygen as a by-product, the O2 changed into O3 or Ozone. By actually modifying the atmosphere, the plants changed the Earth into a more hospitable place for life.
Now animals survive by basically eating green plants or eating other animals that eat green plants. Now the chemical reaction of photosynthesis basically runs backwards. Animals take the glucose from plants, in the presence of oxygen and water, they free that trapped solar energy and use that energy to live, thrive and build more animal tissue. This is called respiration and the by-product of this, as we all know when we exhale and pee, is carbon dioxide and water.
So to recapitulate- sunlight plus green plants in the presence of carbon dioxide and water makes sugar and gives off more water and oxygen. Animals eat plants, breathe in oxygen and use this chemical to get energy out of the sugar and then emit carbon dioxide and water. Presto there you have it – the simple but elegant miracle of life on our planet.
This is Michael Ellis with a Perspective.