Why are fossils important evidence for evolution?

Fossils provide a record of life on Earth from as long as 1 billion years ago, showing how organisms, animals and plants have changed over time. These records can be dated, so they are a physical representation of evolution, such as the way that ancient fish developed a bone in their jaw over time.

According to BioLogos, fossils originating from about 1 billion years ago show that the earliest life on the planet consisted of organisms that were single-celled. The fossils from about half a billion years later show that those single cells had developed into organisms with multiple cells. In other words, the fossils show that organisms evolved over a long period of time, moving from simpler life to more complex life. This pattern continued throughout history, as life forms became more and more complex.

Evolution does not go in a single line, evolving from one form of life to the next. In fact, according to the Smithsonian website, homo sapiens evolved in a large family of other human species, although homo sapiens (the species of humans on the planet now) were the only species to survive.