Key facts about evidence
• There are many different kinds of evidence that we can use to find out about the past.
• Most of this evidence requires fieldwork: e.g. geographers go into the landscape and study landforms, taking measurements or collecting samples.
• Much of our evidence also comes from samples of ice collected from the Antarctic and Greenland ice sheets, and samples of the sea floor.
• The following slides illustrate the types of evidence that have been used to learn about the
Ice Age.

Evidence on land
DEA
• Geographers can identify and map lateral and end moraines to work out the former size of glaciers like this one.
• The moraine in this photo shows how much bigger the glacier was during the ‘Little Ice Age’.

Evidence on land http://commons.wikimedia.org/wiki/File:Terminal_moraine_-
_geograph.org.uk_-_230042.jpg?uselang=en-gb (Rob Burke)
• Geographers can also identify and map moraines in places where glaciers no longer exist today.
• There are lots of moraines in the British Isles, and this helped convince scientists in the 19 th century that there was an Ice Age when ice covered much of the country.

Evidence on land http://commons.wikimedia.org/wiki/File:The_Norber_erratics_-
_geograph.org.uk_-_6893.jpg
(Val Vannet)
• Geographers can identify and map glacial ‘erratics’ like this one. Erratics are boulders that were moved by ice and then dropped in places where the geology is different.
• This helps to work out how far ice sheets extended and the direction of former ice movement.

Evidence on land http://commons.wikimedia.org/wiki/File:Glacial_striation_21149.JPG?
uselang=en-gb Walter Siegmund
• Scratched and polished bedrock (like the striations shown in this image) gives evidence of glacier erosion in the past.
• By measuring the orientation of the glacial striations, geographers can work out the past direction of ice movement.

Evidence from ocean sediments http://commons.wikimedia.org/wiki/Fil e:Joides_resolution_odp.jpg?uselang=e n-gb (ODP)
• Ships like these are able to sample the sea floor by drilling into the sea bed and pulling up ‘sediment cores’.
• The sediment cores can be analysed to look at changes in the sediment which indicate past changes in the ocean environment.
• By analysing the types and shell composition of microscopic marine organisms preserved in the sediment, it’s possible to work out both past sea temperatures as well as past sea levels.
Microscopic foraminifera

Younger sediment above
Older sediment below
Evidence from ocean sediments
• Samples of sea floor can be looked at in cross-section (like this one).
• Changes in the composition of the sediment can be looked at to interpret changes in the ocean environment.
• In this image, the angular pieces of gravel tell us that icebergs floated over this part of the ocean, and as they melted, the gravel they contained sunk to the sea bed and became part of the sea floor sediment.
• Sections of sediment with more ‘ice rafted’ debris like this indicate times when there were more icebergs and therefore also bigger, more extensive ice sheets on land that bordered the sea.
http://commons.wikimedia.org/wiki/File:Sediment-core_PS56_039_xray_hg.jpg?uselang=en-gb Hannes Grobe

Evidence from ice sheets
• Samples of ice can be extracted by drilling into ice sheets and pulling up
‘ice cores’.
• As with ocean sediments, ice layers higher up are younger and ice layers further down are older.
http://commons.wikimedia.org/wiki/File:Icecore_4.jpg?uselang=en-gb
Lonnie Thompson http://commons.wikimedia.org/wiki/File:1998_crprick02_hg.jpg?uselang=en-gb Hannes Grobe

Evidence from ice sheets http://earthobservatory.nasa.gov/Features/Paleoclimatolog y_IceCores/ NASA image
The process of ice coring

Evidence from ice sheets
The ‘0’ here means the modern air temperature.
The Δ means difference from the modern.
Air bubbles trapped in the ice give samples of the atmosphere at the time the snow fell.
LGM
The peaks are warmer ‘interglacials’ and the troughs are colder ‘glacials’.
The longest ice core from Antarctica goes back over
800,000 years!
http://commons.wikimedia.org/wiki/File:Vostok-ice-core-petit.png
• A huge amount of information can be gained from analysing ice cores. By looking at evidence in each layer of ice from the surface downwards, scientists have a time record (because the ice gets gradually older the further down it is).
• In this diagram, an ice core (from Vostok, Antarctica) shows us how atmospheric temperature, carbon dioxide content, and dust content have been changing through time.

Key facts about causes of change
• From the diagram on the previous slide, you can see how climate has been going through cold/warm cycles during the Quaternary Period.
• These cycles relate to regular cycles of variation in how the
Earth orbits the Sun.
• Sometimes the Earth’s orbit is in a pattern that increases the amount of solar energy received far north, and this causes glaciers to shrink (and this is an ‘interglacial’ time).
• At other times the pattern of orbit causes reduced solar energy in the far north, and glaciers expand (and the Earth goes into a ‘glacial’ time).
• These are called ‘Milankovitch’ cycles after the Serbian scientist who first calculated them.
• Watch this short YouTube videoclip for more information about Milankovitch cycles: http://www.youtube.com/watch?v=ZRbpj1JA29M

Key facts about causes of change
• The orbital variations are ultimately the cause for the cold/warm fluctuations of the Quaternary Period, but there are other factors that also affect how warm or cold it gets.
• Notice the similarity between the temperature changes and the atmosphere’s carbon dioxide (CO
2
) levels shown in the previous diagram.
• The changes in CO
2
(which is a ‘greenhouse gas’) reinforce (or
‘amplify’) the warming/cooling caused by changes in the
Earth’s orbit.
• In other words, ↑CO
2 relates to ↑temperature.
• For a longer, and more detailed YouTube video about the nature and causes of Ice Age changes, follow this link on the
BBC website: http://www.bbc.co.uk/learningzone/clips/discoveringthe-origins-of-ice-ages/13533.html

Key facts about causes of change
• There are also other causes of climate change that affect the climate over shorter timescales than the orbital changes.
– Volcanic eruptions (big eruptions put dust and ‘aerosols’ into the atmosphere which temporarily reduce the amount of sunlight).
– Sunspot cycles (the Sun has small variations in how much energy it gives off: more sunspots = more solar energy).
– Ocean circulation changes (changes in the strength and direction of ocean currents has a big effect on how heat is moved around the world, which also affects average temperature).
The smaller-scale variations in climate during the Holocene interglacial (such as the ‘Little Ice Age’) were probably caused by a combination of these three factors.