Although mass extinctions have been caused by asteroids slamming into Earth's surface and other catastrophic events, the Earth's wobbly orbit could regularly signal changes that ultimately prove fatal to almost all species of plants and animals living at a given time.
But, research pointed to even more species-meddling by the Earth's orbit changes every few million years. Scientists also found that mammalian species usually die without provocation from external events that regularly occur on Earth.
Archaeologists have pondered on the question of why this happens roughly 2.5 million years after mammalian species first emerge on the planet. After examining the remains of 80,000 fossilized teeth from 132 different rodents which spanned a 22 million-year period, Jan van Dam at Utrecht University in the Netherlands thinks that he may have the answer to the question.
He conducted an analysis of the fossil fragments, and correlated the results of what he discovered with natural cycles in the Earth's orbit. He concluded that very 2.4 million years, there was a changing of the guard, so to speak. He found that a mass of mammalian extinctions happened at the same that new species were making their emergence on the planet.
Dr. van Dam wrote in the journal Nature that when the Earth is in a very circular orbit, the climate is less changeable -- and at the same time, summer heat will be less extreme. He then noted that milder weather encourages glaciers to grow down from the poles and this action causes a drop in ocean levels. The evidence that the planet's wobbly orbit is to blame for the 2.5 million-year lifespan of many mammal species is "a crucial missing piece in the puzzle," added Dr van Dam.
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