In 1980, when Luis and Walter Alvarez first proposed that an asteroid impact killed off all the dinosaurs 65 million years ago, it started a scientific donnybrook that's still unfolding today.

One of the many spinoffs from that long-running dispute relates to Yellowstone National Park: The idea that impacts might play an active role in Earth's biological and geological record prompted at least three theories about how hot spots like Yellowstone are formed.

Hot spots are long-lived upwellings of magma. Unlike typical volcanoes, they endure for tens of millions of years - long enough to burn tracks across the geological landscape as oceanic or continental plates drift over them.

Robert Smith, a University of Utah geophysicist and researcher at the Yellowstone Volcano Observatory, said the Yellowstone hot spot first manifested itself about 16 million years