Geoscience Reference
In-Depth Information
six
From Ice to Fire
into the holocene
h e very words “Great Ice Age” conjure up images of a
world petrii ed in hundreds of thousands of years of profound
deep freeze, when our skin-clad forebears hunted mammoth,
reindeer, and other arctic animals. Deep-sea borings in the
depths of the Pacii c Ocean, coral growth series from tropical—
and formerly tropical—waters, arctic and Antarctic ice cores,
and concentric growth rings from ancient tree trunks tell a
dif erent story—of constant and dramatic swings in global
climate over the past 730,000 years. Our remote ancestors lived
through wild l uctuations from intense glacial cold to much
shorter warm interglacials that sometimes brought tropical
conditions to Europe and parts of North America. Over these
hundreds of millennia, the earth has been in climatic transition
for more than three-quarters of the time: At least nine glacial
episodes have set a seesaw pattern of slow cooling and then
extremely rapid warm-up at er millennia of intense cold.
Brian Fagan,
Floods, Famines, and Emperors
ice ages and the west
Today, we live in A Relatively cool period that began about
40 million years ago. Over this period, the earth became increasingly cool and
icy, culminating in the Quaternary Period, a dance of advancing ice sheets
(glacial periods) and retreating ice sheets (interglacials) that started two
million years ago. h e most recent glacial period reached its maximum extent
about 20,000 years ago—a period dubbed the “Last Glacial Maximum.” h
e
average global temperature then was about 18°F lower than it is today.
h e earth is currently in a relatively warm interglacial period known as the
Holocene epoch that began 11,000 years ago. Whereas one view holds that
the Holocene is due to end soon, having equaled (or even exceeded) the span
