Name: _____________________________________ Date: __________________ Period: _____
Chapter 15.3: Ice Ages
1. Ice Ages
a. An _____ age, or ________________ period, is a long period of
__________________ cooling during which continental ice _______
cover large areas of Earth’s ____________________.
b. _____________________ periods are the times of _____________
temperatures between the colder _______________ periods.
i. Scientists have found _________________ of several major
glacial _________________ dating from ______ million years
ago to as recent as _________ years ago, and the ice sheets
started to ________________ only 11,000 years ago.
2. Climate
a. Scientists believe that _____ ages begin with a _______-________
decrease in the earth’s ___________________ temperature.
i. This is a ________ of only _____ degrees Celsius.
ii. While the ________________________ was colder during the
last ice ______, there is evidence of ______________ warming
and _____________________ periods during the ice age.
3. Glacial Periods
a. During the most ____________ ice age, approximately _____-______
of the earth’s ________ surface was covered with _______________.
i. There were many ice __________ during the last ice age. Some
ice sheets covered ________________, which were as far south
as ________________ and the ________ River. Some covered
the mountainous regions of ________________, the mountains
of the western _____________ ______________ and flowed
outward from the ________________, Cascades, and ________
___________________ mountain ranges.
ii. This was enough _____ to decrease the _____ _______ by 140
meters compared to ______________.
iii. This ________________ covering of glacial ice ____________
many of today’s __________ features.
4. Causes of Ice Ages
a. Many __________________ have been developed to state a ________
for the ice ___________, and all have explained _________________
cooling and glacial _________________ during interglacial periods.
b. The ______________________________ theory is a widely accepted
theory among _______________________.
Name: _____________________________________ Date: __________________ Period: _____
i. This _______________ proposes that ____________, regular
changes in the earth’s ____________ and __________ of the
earth’s ____________ cause the ice ages.
ii. Three kinds of ______________ changes occur in the way the
___________ moves around the _____.
1. Once change is in the _________ of the earth’s _______.
a. The orbit ____________ from nearly __________
to more ________________ and back to circular
about every ____ _________________ years.
2. A second change is in the ______ of the earth’s axis.
a. Over a _____________ of about ______________
years, the tilt of the ______ varies between ______
degrees and ______ degrees.
3. A third periodic change ____________ from the circular
motion, or ____________________, of the earth’s axis.
a. Precession causes the ________ to change its
___________________.
b. The axis of the ___________ traces a complete
_____________ in space every __________ years.
iii. Milankovitch ___________________ how these three changes
periodically change the ___________________ of solar energy
reaching the earth’s ________________.
iv. ____________________ to support this theory include ______
of sea animals and their ________________ to temperature.
1. Scientists have found that the _____________ of ice ages
found in _______________ sediments closely follows
the cycle of ________________ and warming
__________________ by the Milankovitch theory.
c. There are _________ other theories than the Milankovitch theory.
However, these theories do not give as in depth _________________.
i. Some state reasons being changes in _________ energy caused
by varying amounts of ________ from the sun, _____________
dust blocking the sun’s _____, and __________________ plate
motion changing positions of the ___________________ which
prevent warm __________ currents from reaching regions near
the _____________.