Final answer:
Estimates of current extinction rates rely on the recorded extinction of species, as well as measures of habitat destruction.
Step-by-step explanation:
Estimates of current extinction rates rely on multiple sources of data in addition to the fossil record. One method is based on the recorded extinction of species in the last 500 years, using data from observations and measurements. However, this method underestimates rates of extinction because it does not account for unobserved extinctions and undiscovered species. Another method relies on measuring habitat destruction and using species-area curves to estimate extinction rates. While this method may overestimate the rate of extinction, it is more adapted to situations where existing data is lacking.