Giant ants are species that lived 50 million years ago in the Eocene period. Their fossils were mostly found in tropical Africa in the past. Now paleontologists have found such fossils in the Arctic strata, so they speculated that The Arctic in the New Era has a periodic high temperature stage. The underlying assumptions of the above inference are:. ['The Arctic has historically been connected to the African continent.', 'Giant ants are a species only suitable for survival in high temperature environments.', 'The phenomenon of global warming once appeared in the prehistoric era 50 million years ago.', 'Compared to tropical regions in Africa, biological fossils are easier to preserve in frozen Arctic environments.']