Major geologic events play a critical role in building Earth's timeline. These events, such as volcanic eruptions, earthquakes, and asteroid impacts, leave behind distinct layers of rock and sediment that can be dated using various techniques. By analyzing the sequence of these layers, scientists can piece together a timeline of Earth's history and understand how the planet has evolved over time. Additionally, these events can also cause mass extinctions and drive evolution by creating new habitats and opportunities for species to adapt and thrive. Overall, major geologic events provide important clues for understanding the history and development of our planet.