Alvarez 's hypothesis at the time conflicted over whether an impact was the cause or whether the iridium had been deposited by a supernova from a nearby star , which could have also killed most life on Earth due to gamma ray bursts and cosmic radiation . In order to confirm or rule out this alternative hypothesis , Alvarez worked with Frank Asaro and Helen Michel to determine if the clay layer also contained plutonium-244 , a distinctive isotope that a supernova would also have deposited if it had been the cause . While their initial testing came out as positive for the isotope , it turned out to be a false positive under further scrutiny and testing . This caused Alvarez to abandon the supernova possibility and focus singularly on an impact event being the cause . However , Alvarez was uncertain on how such an impact could have wiped out species all around the world . After investigating the effects of the 1883 eruption of Krakatoa , he determined that a large enough impact could force enough ash and dust into the atmosphere to block out the sun , leading to a global mass extinction
1883 eruption of Krakatoa
1883 eruption of Krakatoa
T. Rex and the Crater of Doom