Final answer:
Throughout Earth's history, there have been five key mass extinction events marked by dramatic biodiversity losses, occurring approximately 450, 360, 250, 205, and 65 million years ago. These events are often followed by periods of evolutionary radiation, where new species evolve to fill the ecological gaps. The fossil record is the primary source of information about these significant changes in Earth's biological diversity.
Step-by-step explanation:
Throughout Earth's evolutionary history, there have been several periods of both evolutionary radiation and mass extinctions. These events are captured within the geological record and have played a crucial role in shaping the diversity of life we see today. Mass extinctions have been pivotal moments where a significant percentage of Earth's species were wiped out. There are five well-documented mass extinctions:
- The end-Ordovician (around 450 million years ago)
- The Late Devonian (360 million years ago)
- The end-Permian (250 million years ago) also known as the 'Great Dying'
- The end-Triassic (205 million years ago)
- The end-Cretaceous (65 million years ago) which led to the demise of the dinosaurs
These extinctions are marked by a sharp increase in the percentage of species that vanished from the fossil record and often coincide with the end of geological periods. Following each of these mass extinction events, periods of evolutionary radiation typically occurred, where new life forms diversified to fill the vacant ecological niches. These radiations allowed for the fast evolution and speciation of surviving organisms and the initiation of new lineages.