Evolution is a scientific theory used by biologists. It explains how animals and plants changed over a long time, and how they have come to be the way they are. The Earth has been around for a very long time, about 4.5 billion years. During the first three billion years on Earth, there were only bacteria. Jellyfish were the first species to appear around 700 million years ago.
We know that living things have changed over time because we can see their remains in the rocks. These remains are called ‘fossils’. We know that the animals and plants of today are different from those of long ago. The further we go back the more different the fossils are.
Scientists know evolution has taken place because of the research they have done. Scientists have been collecting evidence for more than 150 years. At the same time, evolutionary questions are still being researched by biologists. The theory of evolution is the basis of modern biology. Nothing in biology makes sense without it.