Hi, I'm Sean Tvelia. We're here at Suffolk County Community College to answer the question, "What year did the dinosaurs get hit by a meteorite?" Geologists measure time in two different ways. The first, relative dating, allows us to put events in order based on their placement in the rock record. The lower or the deeper an event is in the Earth's structure, the older it is. The second way we measure time is through absolute dating that utilizes the radioactive decay of radioactive isotopes to determine the actual number of years before the present when something occurred. Dinosaurs disappeared on our planet right below a layer that geologists refer to as the KT, or appropriately these days, the KP boundary. This is a worldwide layer that separates the Cretaceous time period from the Tertiary. Below the layer, lots of dinos, above the layer, not so many dinos. Now the relative time tells us that the dinosaurs perished at the end of the Cretaceous period, but using the Uranium and lead isotopes that are available within the KT boundary, geologists have determined that the dinosaurs went extinct roughly 64 million years ago. Now it's impossible give an exact date because we have instrumental errors that are available and just not the ability to see what the exact year was, but within about 1.2 to 1 million years, geologists have determined that the dinosaurs went extinct 64 million years ago.