Earth's Wobbles Blamed for Mammals' Deaths

Wobbles or variations in the Earth's orbit and tilt are associated with extinctions of rodent and mammalian species, Dutch scientists reported Wednesday in the journal Nature.

They studied rodent fossil records in central Spain dating back 22 million years and found that the rise and fall of mammal species was linked to changes in Earth's behavior, which caused cooling periods.

The researchers found two cycles corresponding to the disappearance of rodent species. One lasted 2.4 million years and was linked to variations in Earth's orbit. The other was a 1.2-million-year cycle relating to shifts in Earth's tilt on its axis.