The Evolution in Water

Biology occupies itself with living organisms. These organisms take in energy and later dispose of it, often in a changed way. In contrast to dead material, their building blocks react with elements of the body all the time. This metabolism must have started some time long, long ago in the first cell.

What were the conditions in those times?

Life began for the first time 3000 million years ago. In that time, our planet existed with completely different conditions and a different atmosphere. There was no iron or uranium, for example, but there were proteins, carbohydrates and other organic molecules, which can be formed spontaneously.
The energy for the chemical reactions, which is always necessary to put together two molecular building blocks, was provided by lightning, the heat of volcanoes and radioactive radiation.
This is believed to be how 'original molecules' assembled and established the first metabolism. A prerequisite to maintain life on earth was to reproduce, of course. This was the only way to preserve and to pass on previous achievements.

Why don't all living beings look the same?

At first, only a single living cell had formed. This one-celled organism reproduced and tried to produce as much offspring as possible. With time however, small errors occurred in the offspring, which changed the organism in one way or the other. If the altered offspring managed to survive successfully in the environment despite its different appearance, it had found its place in nature. It too reproduced and its progeny looked like it. Now there were already two species on the planet. This incident happened repeatedly over years and years. You can imagine this as a tree, which begins with a trunk and afterwards starts to branch out. Nevertheless, the trunk stays the trunk and the branch becomes a branch. Many species died out, though, because they were not able to adapt to changes in the environment.