Answer:
There are several facts that linked life to a common origin such as:
- Comparative anatomy, where different species have common traits. This includes homology and analogy, vestigial structures.
- Fossil record.
- Species distribution in different continents, some others.
I believe the most valuable evidence is that DNA is the molecule that carries information in all living things ( eukaryotes and prokaryotes) even viruses contain either DNA o RNA. Is difficult to think that life started in different ways but then converged in the same kind of molecule to carry the information.