198
I
n the early 19th century, there
were contradictory explanations
for the development of Earth’s
landforms, plants, and animals.
Supporters of catastrophism argued
that a series of destructive shocks,
such as the Great Flood described in
the Bible, had re-formed the surface
of the planet many times, reshaping
existing mountains, lakes, and rivers
and wiping out many plant and
animal species. In contrast, followers
of uniformitarianism contended that
Earth’s features were the result of
continuous and uniform natural
processes of erosion, sedimentation
(the depositing of particles carried
by fluid flows), and volcanism.
Detailed geological studies
demonstrated that neither camp
was right. They established thatEarth’s history has been a process
of slow change, punctuated by
catastrophic events. The study
of glaciers, and the landforms they
create, informed these ideas. After
observing parallel striations in rocks
of the Swiss Alps, German–Swiss
geologist Jean de Charpentier (or
Johann von Charpentier) postulated
that glaciers in the Alps had once
been more extensive and had
caused the scratches as they moved
and their sediment cut into the rock.
Geologist Jens Esmark drew similar
conclusions in Norway.Glacier movements
Swiss zoologist Louis Agassiz
developed Charpentier’s and
Esmark’s ideas further. In 1837,
he proposed that vast sheets of
ice had once covered much of the
northern hemisphere, from the
North Pole to the Mediterranean and
Caspian coastlines. Agassiz also
undertook some detailed studies
of glacier movement in Switzerland
and published his Études sur lesAnimals enter Noah’s ark in a
depiction of the Great Flood described
in the Bible. Catastrophists believed that
the Great Flood was one of the formative
shocks that shaped the geology of Earth.IN CONTEXT
KEY FIGURE
Louis Agassiz (1807–73)BEFORE
1795 Scottish geologist James
Hutton argues that erratic
boulders (rock fragments that
are different from the
underlying rock) in the
Alps were transported by
moving glaciers.1818 In Sweden, naturalist
Göran Wahlenburg publishes
his theory that ice once
covered Scandinavia.1824 Danish–Norwegian
mineralogist Jens Esmark
theorizes that glaciers were
once larger and thicker and
had covered much of Norway
and the adjacent seafloor.AFTER
1938 Serbian mathematician
Milutin Milankovic ́ publishes
a theory to explain the
recurrence of ice ages based
on changes in Earth’s orbit
around the Sun.THE GLACIER
WAS GOD’S
GREAT PLOW
ANCIENT ICE AGES
US_198-199_Ancient_Ice_Age.indd 198 12/11/18 6:25 PM