Final answer:
Biodiversity is shaped by two key evolutionary processes: speciation, which creates new species, and extinction, which removes species. The balance and fluctuations between these processes determine the rise and fall of biodiversity levels over time.
Step-by-step explanation:
The two evolutionary processes that determine the world's current biodiversity are speciation and extinction. These processes serve as the 'birth' and 'death' of species, contributing to the dynamic nature of biodiversity throughout geological time. When the rate of speciation exceeds that of extinction, biodiversity increases, and conversely, it decreases when extinction rates are higher. These fluctuations are evident from the fossil record and have led to dramatic changes in biodiversity over Earth's history.