Final answer:
Mass extinctions are rapid and catastrophic events leading to widespread species loss, while background extinctions occur at a slower, more continuous rate. The Late Permian and Cretaceous-Paleogene are examples of mass extinctions, with the former being the most devastating. A sixth mass extinction, influenced by human activity, is currently underway.
Step-by-step explanation:
Mass extinctions and background extinctions are two different phenomena observed in the history of life on Earth. Mass extinctions refer to periods in which a large proportion of species die out in a relatively short geological timeframe due to catastrophic events. These events, such as asteroid impacts or massive volcanic eruptions, cause drastic environmental changes that make it difficult for many species to survive. The most famous example is the Cretaceous-Paleogene extinction event 65 million years ago that caused the demise of the dinosaurs due to an asteroid impact. Background extinctions, on the other hand, are the standard rate of extinction that occurs as a part of natural selection and environmental changes. These extinctions happen continuously and at a much slower rate than mass extinctions.
Historically, background extinctions have accounted for most species losses, but mass extinctions lead to sudden and significant biodiversity loss. The Late Permian mass extinction is considered the most devastating, likely caused by significant climate warming and ocean chemistry changes due to volcanic activity. Currently, there is evidence of a sixth mass extinction, largely attributed to human actions like climate change and habitat destruction.