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Destructio

n :BY NOT

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What is IceAge ?

An ice age, is a period of long-termreduction in the temperature of

the Earth's surface and atmosphere,resulting in the presence or expansion ofcontinental ice sheets, polar ice sheets

and alpine glaciers. Within a long-term iceage, individual pulses of cold climate are

termed "glacial periods" and intermittentwarm periods are called "interglacials".

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In 1840, Louis Agassizobserved unique glacialfeatures in Scotland.

He found scratches ona rocky hillside nearEdinburgh like thosemade by glaciers.

He argued that Scotlandhad recently been coveredin a thick ice sheet.

ice scratches

Evidence of Ice

AgesEvidence 1:Scotland

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Agassiz amassed more evidence from landforms and boulderclays to support his idea of a Great Ice Age in recent times.

Glen Roy, Scotland

Parallel marks showformer level of anice-dammed lake

Evidence 2: Ice Agelandforms

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Pollen

MammothBeetles

Fossil discoveries alsosuggested that climate hadrecently been much colder.

Beetles and pollen grainsfound in sediments associatedwith the boulder clays wereidentified as types known onlyfrom theArctic tundra today.

Woolly mammoths founddeep frozen in Siberia hadfur adapted to tundra life.

Evidence3:Fossils

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8/16/12 Annual layers in ice

Drilling cores

Evidence 4: Ice

Archive In the early 1980s,there was anothermajor breakthrough.

Cores were drilledin the

polar icecaps

revealingannual layers ofsnow going backthousands of years.

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When the Last Ice Age was at its maximum, ice sheets coveredmuch of Europe and North America.

So what actually caused it?

Cause of Ice Ages

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In the 1940s, Milankovi wondered whetherwobbles in theEarths orbit around the Sun could explain multiple Ice Ages by

changing the amount of heating reaching the Earth

Milutin Milankovi(1879-1958)

Cause 1: Orbitalwobbles

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Milankovi added up all the orbital wobbles and predicted thatice ages should occur in regular cycles - probably happening

every hundred thousand years or so.

Cause 2:

Cycles

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In 1960s, deep sea records showed that Milankovi was right!

cold

hot

1000s of years before present

The Oil Drum

The Earths climate had repeatedly blown hot and cold withice age cycles happening every hundred thousand yearsjustas Milankovi had predicted.

Cause 2

Contd.

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NOAA

Greenhouse Gas levelsdropped during Ice Ages

Last Ice Age =Low Greenhouse Gas

The second idea is thatchanges in greenhousegas levels were to blame.

Greenhouse gases help tosoak up sunlight and keepthe Earth warm.

Air bubbles in ice coresshow that levels fell duringIce Ages so this mayhave sped up cooling.

Cause 3: GreenhouseGases

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Gulf Stream warms the Arctic Some scientists believethat ocean currents likethe Gulf Streamwere important.

This current helpswarm up the Arctic. If itswitched off this

would cool the Arcticfurther andincrease the likelihood ofan Ice Age

Cause 4: Ocean

Currents

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