The Ice Ages

NSA

© Howard Falcon-Lang

Talk outline

Part 1: How was the Ice Age first discovered?Investigation: Beetles as evidence of past climate

Part 2: What causes Ice Ages?Investigation: The Day After Tomorrow?

Part 3: What was Europe like in the Last Ice Age?

Discovery (1): The Floodwww.scottishgeology.com/gallery/image02.html

• Early geologists noticed a layer of sticky clay with boulders over much of Europe. Had it been deposited by a catastrophic flood like Noah’s Flood in the Bible?

www.eriding.net/media/photos/geograp/_geo_lpp_007_boulder_clay.jpg

boulder

Discovery (2): The Alps

en.wikipedia.org/wiki/Image:Johann_von_Charpentier.jpg

• In the early 1800s Jean de Charpentier observed the advance and retreat of glaciers in the Alps and studied the kind of deposits they left behind.

1820s 1850s

Glacial retreat

Discovery (3): Scotland• In 1840, Louis Agassiz observed similar glacial features in Scotland.

• He found scratches on a rocky hillside near Edinburgh like those made by glaciers.

• He argued that Scotland had recently been covered in a thick ice sheet.

en.wikipedia.org/wiki/Image:Louis_Agassiz-2.jpg

ice scratches

Discovery (4): Ice Age landforms

www.geo.umn.edu/courses/4703/Spring00/5-NorthShore/images/striations.jpg

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

Glen Roy, Scotland

www.swisseduc.ch/glaciers/earth_icy_planet/glaciers15-en.html?id=15

Parallel marks show former level of an ice-dammed lake

Discovery (5): Fossilswww.colby.edu/geology/gifs/M.nelsoni.jpg

www.aip.org/history/climate/images/Dryas_octopetala.pollengrain.jpgen.wikipedia.org/wiki/Image:Mammoth_mg_2791.jpg

Pollen

MammothBeetles

• Fossil discoveries also suggested that climate had recently been much colder.

• Beetles and pollen grains found in sediments associated with the boulder clays were identified as types known only from the Arctic tundra today.

• Woolly mammoths found deep frozen in Siberia had fur adapted to tundra life.

Discovery (6): Chemical studies• In the 1960s, chemical studies offered more evidence for an Ice Age.

• They showed that the amount of heavy oxygen in seawater was controlled by the size of the polar ice cap.

• When polar icecaps were bigger there was more heavy oxygen in the sea and vice-versa.

More ice

More heavy oxygen in sea

© Howard Falcon-Lang

Discovery (7): Microscopic animalswww.ucl.ac.uk/GeolSci/micropal/images/fora/fora020.gif

nj.usgs.gov/nawc/images/68brcore.jpg

Foraminifera

Borehole core

• In 1967, Shackleton used this fact to learn more about the Ice Age.

He studied heavy oxygen in bugs called foraminifera fossilized in deep sea mud.

• The bugs proved that the icecaps had been bigger at certain times in the past.

Discovery (8): Ice Archiveen.wikipedia.org/wiki/Image:GISP2_1855m_ice_core_layers.png

Annual layers in ice

• In the early 1980s, there was another major breakthrough.

• Cores were drilled in the polar icecaps revealing annual layers of snow going back thousands of years.

Sepp Kipfstuhl, Alfred-Wegener-Institut

Drilling cores

Discovery (9): Air bubbles

en.wikipedia.org/wiki/Image:GISP2_1855m_ice_core_layers.png

© CSIRO

• Scientists found air bubbles in the ice that had got trapped when the snow had first fallen.

• Bubbles showed how much greenhouse gas there had once been in the atmosphere.

• As we will see later this was important for understanding what causes Ice Ages.Air bubbles in ice

Investigation 1

Using beetles as evidence of past climate

www.ndsu.nodak.edu/instruct/ashworth/aapg_perspectives.pdf

Cause (1): Introduction

• When the Last Ice Age was at its maximum, ice sheets covered much of Europe and North America. So what caused it?

NASA

Cause (2): Many Ice Ages© Ian and Tanya West

• By studying the layers of gravel left behind by the ice, geologists figured out that there hadn’t been just one Great Ice Age.

Ice age layers

• Rather, over the last two and a half million years, there had been many ice ages each separated by a short warmer period.

Cause (3): Orbital wobblesen.wikipedia.org/wiki/Milutin_Milanković commons.wikimedia.org/wiki/Image:Milankovitch-cycles_hg.png

• In the 1940s, Milanković wondered whether wobbles in the Earth’s orbit around the Sun could explain multiple Ice Ages by changing the amount of heating reaching the Earth

Milutin Milanković (1879-1958)

Cause (4): Cycles

• Milanković added up all the orbital wobbles and predicted that ice ages should occur in regular cycles - probably happening every hundred thousand years or so.

en.wikipedia.org/wiki/Image:Milankovitch_Variations.png

Cause (5): Sun’s pacemaker

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

cold

hot

1000s of years before present

© The Oil Drum

• The Earth’s climate had repeatedly blown hot and cold with ice age cycles happening every hundred thousand years just as Milanković had predicted.

Cause (6): The Big Question

• But one big question remained: Exactly how did changes in the amount of solar energy reaching the Earth trigger Ice Age cycles?

• So far there are no firm answers but three good ideas

Cause (7): Colour of the Poles

• The first idea is that as the Earth cooled, green forests in the far north were replaced by white ice.

• Ice reflects back more of the sun’s energy, so this would have caused further cooling, leading to an Ice Age.

Absorbs energy: Warming

Reflects energy: Coolingen.wikipedia.org/wiki/Image:AntarcticaDomeCSnow.jpg

Cause (8): Greenhouse Gases

© NOAA

Greenhouse Gas levels dropped during Ice Ages

Last Ice Age =Low Greenhouse Gas

• The second idea is that changes in greenhouse gas levels were to blame.

• Greenhouse gases help to soak up sunlight and keep the Earth warm.

• Air bubbles in ice cores show that levels fell during Ice Ages so this may have sped up cooling.

Cause (9): Ocean CurrentsGulf Stream warms the Arctic

• The third idea is that ocean currents like the Gulf Stream were important.

• This current helps warm up the Arctic. If it switched off this would cool the Arctic further and increase the likelihood of an Ice Age

www.sott.net/image/image/tmp/1168547904.692692.7800/le-gulf-stream.jpg

Practical Exercise 2

The Day After Tomorrow?

commons.wikimedia.org/wiki/Image:Perito_Moreno_Glacier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG

Ice Age Europe (1): Geography20,000 years ago

www.geocities.com/reginheim/europeiceage.gif

• Europe was very different at the height of the Last Ice Age.

Thick ice sheets in north

Frozen tundra in centre

Conifer forests in south

• We will focus on the tundra region of southern England.

Ice Age Europe (2): Coastswww.uwgb.edu/dutchs/EarthSC202Notes/GLACgeog.HTM

Ice sheet

Tundra

• With so much water locked up as ice, sea level was much lower in the Last Ice Age and Britain was attached to mainland Europe.

• This allowed humans, animals and plants to migrate far and wide.

Ice Age Europe (3): Plants• Fossil pollen show that southern England was a mostly treeless tundra.

• The main plants were grass and sedge. Together with the arctic willow, dwarf birch, juniper and the mountain avens, these plants formed a low growing carpet.

The mountain avens (Dryas) was common in the Ice Age tundra

en.wikipedia.org/wiki/Mountain_Avens

Ice Age Europe (4): Mammalscommons.wikimedia.org/wiki/Image:Woolly_mammoth_siberian_tundra.jpg

• Many large animals lived on the tundra south of the ice sheet. Fossil bones of the woolly mammoth, woolly rhino, reindeer, horse, musk ox, lion, and spotted hyaena have been found.

Ice Age Europe (5): Neanderthals

en.wikipedia.org/wiki/Image:Homo_sapiens_neanderthalensis.jpg

en.wikipedia.org/wiki/Image:Neanderthal_2D.jpg

• Early humans like Neanderthal Man also survived on the tundra where they hunted herds of mammoth.

• Their fossils show they had thickset bodies, which were adapted to the extreme cold.

• They were probably wiped out by competition with our modern human ancestors who arrived on the scene about thirty thousand years ago.

Ice Age Europe (6): Our ancestors

Art in the Lascaux Cave, France

en.wikipedia.org/wiki/Lascaux

• Fossils show that our modern ancestors arrived in Europe right at the end of the Last Ice Age.

• They left spectacular artwork on cave walls across the continent.

• The most famous cave art is in the Lascaux Cave of France

Ice Age Europe (7): Melt wateren.wikipedia.org/wiki/Image:Gordale_scar_from_bottom.jpg wikimedia.org/wiki/Image:Malham_Cove.jpg

• As the Last Ice Age came to an end, gorges and waterfalls were cut by melt water floods across northern Europe

Gordale Scar and Malham Cove in Yorkshire

ancient waterfall

Ice Age Europe (8): Sea Level

en.wikipedia.org/wiki/Image:Post-Glacial_Sea_Level.png

• As ice sheets melted, sea level rose by 120 metres reaching present levels about eight thousand years ago.

Ice Age Europe (9): Rebound

Sea caves left high and dry on Arran

• Those areas that had been pressed down by the weight of thick ice sheets then rebounded upwards.

• This left beaches and sea-cliffs around the Scottish coast high and dry.

The Ice Ages

NSA

© Howard Falcon-Lang