a. Mass extinctions have drastic effects on biodiversity. Wiping out populations of organisms can result in reduced competition for other species, increased resources and completely different environments which foster different adaptations.
b. Biodiversity has drastically changed since the origin of life. The initial organism began as a prokaryote (single celled organism with out membrane bound organelles). Today, there are plants, animals, prokaryotes, fungi, etc. Biodiversity refers to the variety and variation between the numerous species on earth. In the initial phases of Earth's biological development organisms were simple and lacked diversity. today organisms are complex and there are billions of species throughout the planet.