Final answer:
Fossil evidence and DNA analysis are two types of observations that demonstrate evolution, showing changes in species over time and genetic markers of common ancestry.
Step-by-step explanation:
Two types of observations that allow us to conclude that evolution is an observable fact include the extensive fossil evidence and the detailed analysis of DNA in living organisms.
Fossil records show us that organisms from the past differ significantly from those that exist today, which suggests a pattern of gradual changes leading to modern species.
Additionally, DNA analysis helps us identify genetic similarities and differences among species, providing insights into how species have diverged from common ancestors over time.
For example, through studying DNA, we can observe that the genetic material of living organisms retains markers of their evolutionary past, such as shared sequences that indicate common ancestry.
These observations are powerful because they are consistent and converge from different scientific fields, reinforcing the credibility of evolution as a scientific fact.