Agence France-Presse: Melting of methane ice unleashed runaway global warming some 635 million years ago, according to a study released Wednesday that has implications for today’s climate-change crisis. Release of the potent greenhouse-gas, at first in small amounts and then in massive volumes, brought a sudden end to the planet’s longest Ice Age, its authors believe. During the “Snowball Earth” era, Earth froze over completely, with glaciers that crept down into the tropics and possibly …