of farming, tionof toics and ing and science and all t—aken placeypical patcerglacials ed as little as eigs ten th anniversary.
t is, ill very muc’s just a some of t period of glaciation, aroundty t 30 percent of tenpercent still is—and a furt is in a state of permafrost. ters of all ter on Eart botuation t may be unique in Eartory. t ters t glaciers even in temperate places suce natural, but in fact it is a most unusual situation for t.
For most of its ory until fairly recent times ttern for Earto be ice anyed about fortymillion years ago, and o not bad at all. Ice ages tend to evidence of earlier ice ages, so tcuregro it appears t seventeen severe glacial episodes in t 2.5million years or so—t coincides us in Africafolloed culprits for t epocion of t disrupting air flos. India, once an island, ers into t forty-five million years, raising not only t alsot tibetan plateau be tonly cooler, but diverted made to more susceptible to long-term c five millionyears ago, Panama rose from ting ts betlantic, and cterns of precipitation across at least ofAfrica, of trees and go looking for a nehe emerging savannas.
At all events, inents arranged as t appears t iceerm part of our future. According to Jo fifty more glacialepisodes can be expected, eacing a haw.
Before fifty million years ago, Eart o be colossal. A massive freezing occurred about 2.2 billion years ago, follo—so large t some scientists are noo t occurred as tion is more popularly knoh.
“Snoions. tbecause of a fall in solar radiation of about 6 percent and a dropoff in tion (orretention) of greenially lost its ability to o its . Itbecame a kind of all-over Antarctica. temperatures plunged by as muc. tire surface of t may o itudes and tens of yards tropics.
t tes iceevery asfirmly t t er someosynt t, but as youo peer t, ice quickly becomes opaque and after onlya feies ed. One is t alittle ocean er did remain exposed (pera spot); t maybe t it remained translucent—a co