Scientists have tools that help them to answer these questions. They believe that life appeared and flourished only once on earth, and that all living things are related to one another, and possibly the descendants of a single cell. In this book he proposed the theory of Evolution. Individual organisms differ from one another. The organisms that are well adapted to the environment have the most descendants.
Inherited adaptations lead to changes in the organisms over the generations.
Let's look at some examples to see how this works. The earliest life bearing oceans were full of all sorts of chemicals. The first cells were able to use the chemicals for their life processes. Over time, the chemicals were used up and became harder to find. Some cells adapted by making chlorophyll so that they could make food from carbon dioxide, water.