Climates of Geologic Time Current Weather Finish Ice Core Research Overview and Historical Perspective The Pleistocene and Holocene For Next Class: Read.

Climates of Geologic TimeCurrent WeatherFinish Ice Core ResearchOverview and Historical Perspective The Pleistocene and Holocene

For Next Class: Read Ch. 11 (pp. 351-354)Reminder: Exam 2 on March 4th

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Climates of Geologic Time

Geologic time scale: standard division of Earth history into eons, eras, periods, and epochs based on large-scale geological events

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Climates of Geologic Time

Absence of bedrock and plate tectonics complicate the reconstruction of past climates

However, available evidence supports some conclusions regarding the climate over geologic time

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Climates of Geologic Time

Geologic evidence supports interval of extreme climate fluctuations beginning about 570 million years ago Corresponds to transition between the

Precambrian and Phanerozoic Eons Abrupt changes between extreme cold and

tropical heat

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Climates of the Pleistocene Ice Age

Plate tectonics has not been a major factor in climate change over the past two million years

Climate of the last two million years favored the development of huge glacial ice sheets

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Climates of the Pleistocene Ice Age

Historical Perspective Glacial theory proposed in the mid-1800s by

Swiss naturalist Louis Agassiz Geologist Thomas C. Chamberlin proposed

that the Ice Age had involved multiple advances and recessions of glacial ice sheets • Geologists subdivided the Pleistocene Epoch into

four glacial stages

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Climates of the Pleistocene Ice Age

Climate and Glaciers The difference between ice mass gain and ice

mass loss over the course of one year is the glacier’s mass balance• If a glacier loses more ice than it gains, its mass

balance is negative glacier thins and shrinks

• If a glacier gains more ice mass than it loses, its mass balance is positive

glacier thickens and expands

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Climates of the Pleistocene Ice Age

Climate and Glaciers Glacial climates favor positive

mass balance Interglacial climates favor

negative mass balance Climate shifted between

glacial and interglacial numerous times during the Pleistocene

Definitions

What is the difference between a glacial and interglacial?

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Climates of the Pleistocene Ice Age

Glaciers and Landscapes During major glacial

climatic episodes of the Pleistocene Epoch, the Laurentide ice sheet formed over east-central Canada and spread into the U.S.

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Climates of the Pleistocene Ice Age

Chronology and Temperature Trends Oxygen isotope analysis of deep-sea

sediment cores shows numerous fluctuations between major glacial and interglacial climatic episodes over the past 600,000 years

A relatively mild interglacial episode, referred to as the Eemian, began about 127,000 years ago and persisted for nearly 7000 years• Followed by numerous periods of glacial and

interglacial climates

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Climates of the Pleistocene Ice Age

Chronology and Temperature Trends Last major glacial climatic episode began

about 27,000 years ago and reached its peak about 20,000 to 18,000 years ago

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Climates of the Pleistocene Ice Age

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Climates of the Pleistocene Ice Age Younger Dryas: relatively cool episode

from 11,000 to 10,000 years ago• Began abruptly when glacial ice lobes

disrupted drainage patterns Weakened the meridional overturning

circulation, which in turn diminished the warm water flowing into the central and northern North Atlantic

• Cooled surrounding lands

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Climates of the Holocene

The Holocene Epoch is the present interglacial Glacial ice withdrew from North American

Great Lakes region about 10,500 years ago• Civilization and agriculture developed

Holocene has had spatially and temporally variable temperature and precipitation