The Ice Ages Presenter notes: Its hard to believe that only 20,000 years ago, the Earth was in the grip of a Great Ice Age. Most of the British Isles were covered by an ice sheet up to three kilometres thick. Southern England lay just south of the ice and was a treeless tundra inhabited by herds of woolly mammoths. However, this Great Ice Age was only the most recent of a series of ice ages that have occurred over the past 2.5 million years. In this talk we will learn more about the Last Ice Age, how it was discovered and what caused it and earlier 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? Presenter notes: In this talk we will discover more about Ice Age Earth. In Part 1, we will investigate how geologists first discovered that the Earth had been in the grip of an Ice Age until recently. In the investigation that follows we will learn about how fossil beetles can provide information about the climate of the Ice Age. In Part 2, we will think about what causes Ice Ages. In particular we will see how little wobbles in the Earths orbit around the Sun are the most likely trigger. In the investigation that follows we will watch the movie, The Day After Tomorrow, which deals with the start of a new Ice Age. We will discuss how much of this movie is fact and how much is fiction. In Part 3, we will explore what Europe was like at the height of the Last Ice Age. We will understand how this Ice Age completely changed the kind of animals and plants present and even the shape of the coastline. Part 3: What was Europe like in the Last Ice Age? Discovery (1): The Flood
boulder Presenter notes: So, onto our first topic, how was the Ice Age first discovered? Throughout the eighteenth century early geologists noticed a thick layer of sticky clay across much of Europe. Elsewhere giant boulders were found scattered across the landscape. How had these rocks reached their final resting place? Many believed that this was clear evidence for Noahs Flood in the Bible. After all it would have required incredible power to move the giant boulders around. But was there an alternative explanation? Early geologists noticed a layer of sticky clay with boulders over much of Europe. Had it been deposited by a catastrophic flood like Noahs Flood in the Bible? Discovery (2): The Alps 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 Presenter notes: Scientists had the first inkling that the boulder clay may not been deposited by Noahs Flood in the early 1800s. At that time, the worlds climate was a bit colder than now. Glaciers in the French Alps started to advance threatening towns and villages. Later they retreated leaving behind a big pile of rocky debris. Jean de Charpentier was one of the first people to study such glacial deposits. Glacial retreat en.wikipedia.org/wiki/Image:Johann_von_Charpentier.jpg 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. Presenter notes: De Charpentier showed his glacial deposits to a young Swiss geologist called Louis Agassiz. In 1840, Agassiz toured around Scotland and saw tell-tale signs that the Scottish landscape had earlier been shaped by ice like those examples hed seen in the Alps. One bit of evidence that particularly excited him were glacial scratches on a rocky hillside near Edinburgh. Agassiz argued that Scotland had once been covered by a thick ice sheet. ice scratches en.wikipedia.org/wiki/Image:Louis_Agassiz-2.jpg Discovery (4): Ice Age landforms
Parallel marks show former level of an ice-dammed lake Presenter notes: Agassiz spent much of his life touring round the world searching for more evidence to support his idea of a Great Ice Age in the recent past. In Scotland he found grand U-shaped valleys which had been cut by glaciers thousands of years earlier. He also found the mounds of rocky debris left behind when they melted. At Glen Roy, he saw parallel marks on the hillside and realized that these indicated the former levels of a lake that had become temporarily dammed by ice sheets. Glen Roy, Scotland Agassiz amassed more evidence from landforms and boulder clays to support his idea of a Great Ice Age in recent times. Discovery (5): Fossils Fossil discoveries also
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. Pollen Presenter notes: At time when on, the evidence for a Great Ice Age got stronger and stronger. Fossil remains of beetles and pollen grains were found in sediments associated with the boulder clay across Britain and North America. These were of a type that are only found in the Arctic today. The remains of giant woolly mammoths and woolly rhinos were also uncovered deep frozen in Siberian glaciers, the evidence of their thick shaggy hair suggest that they were adapted to chilly weather. Here was clear fossil evidence that the climate had been much colder in the recent past. Beetles Mammoth en.wikipedia.org/wiki/Image:Mammoth_mg_2791.jpg 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. Howard Falcon-Lang More ice Presenter notes: In the 1960s chemical studies offered more evidence for a recent Ice Age. It had long been known that oxygen came in two main types heavy and light. It was also known that the amount of heavy oxygen in seawater was controlled by the size of the polar icecaps. So when the icecaps were really big, there was more heavy oxygen in the sea, and when icecaps were small, there was less heavy oxygen in the sea. As we will see in the next slide, this was soon to provide further evidence for a recent Ice Age. More heavy oxygen in sea Discovery (7): Microscopic animals
Foraminifera 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. Presenter notes: In 1967, a Cambridge geologist called Nick Shackleton used this fact to learn more about the Ice Ages. He studied heavy oxygen in the fossil shells of microscopic animals called foraminifera found in deep sea muds. This showed him how heavy oxygen levels had changed in the sea over the last million years. The bugs showed that the icecaps had been much bigger in the recent past and the Earth had been gripped by Ice Ages at various times. nj.usgs.gov/nawc/images/68brcore.jpg Borehole core Discovery (8): Ice Archive
en.wikipedia.org/wiki/Image:GISP2_1855m_ice_core_layers.png 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. Presenter notes: In the 1980s another exciting discovery came to light. Scientist started to drill deep cores down into the ice sheets of Greenland and Antarctica. They discovered that the ice contained annual layers, each layer representing one years snow fall. The ice cores provided a record of snowfall going back many thousands of years. Drilling cores Sepp Kipfstuhl, Alfred-Wegener-Institut Annual layers in ice Discovery (9): Air bubbles
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. Presenter notes: Most exciting of all was the fact that tiny air bubbles were locked up in the ice. These had become trapped when the snow had first fallen. By analyzing the air it became possible to work out the make-up of the atmosphere back through time. This work showed how the amount of greenhouse gases in the air had changed over time. As we will see later this was really important for understanding what causes Ice Ages. CSIRO Air bubbles in ice en.wikipedia.org/wiki/Image:GISP2_1855m_ice_core_layers.png Investigation 1 Using beetles as evidence of past climate
Presenter notes: Before we go on to look at what causes Ice Ages, lets first think a little more about how we know that there was an Ice Age in recent times. In this first investigation we will study fossil remains of beetles and see what they can tell us about the climate of the recent past. Cause (1): Introduction
Presenter notes: When the Last Ice Age was at its maximum, 20,000 years ago, ice sheets spread over much of Europe and North America. In this second part, we will investigate what causes Ice Ages. NASA When the Last Ice Age was at its maximum, ice sheets covered much of Europe and North America. So what caused it? Cause (2): Many Ice Ages Ice age layers
Ian and Tanya West Ice age layers Presenter notes: For a very long time, geologists had known that there hadnt been just one Ice Age. By studying the layers of gravel left behind by ice sheets, they knew that there had been many ice ages over the past 2.5 million years, each separated by a short warm period. By studying the layers of gravel left behind by the ice, geologists figured out that there hadnt been just one Great Ice Age. 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 wobbles
en.wikipedia.org/wiki/Milutin_Milankovi commons.wikimedia.org/wiki/Image:Milankovitch-cycles_hg.png Presenter notes: In the 1940s, a Yugoslavian mathematician came up with a great idea to explain why the Earth seemed to flip in and out of ice ages. He worked out that as the Earth orbited the Sun it wobbled on its axis. Although these wobbles were tiny, they had huge effects on the amount of heat reaching the Earth. Could this be enough to push the Earth in and out of Ice Ages? Milutin Milankovi ( ) In the 1940s, Milankovi wondered whether wobbles in the Earths orbit around the Sun could explain multiple Ice Ages by changing the amount of heating reaching the Earth Cause (4): Cycles en.wikipedia.org/wiki/Image:Milankovitch_Variations.png Presenter notes: There were lots of different wobbles in the Earths orbit. When Milankovic had added them all up (a difficult sum!) he predicted that they would cause Ice Ages in a regular cycle, say once every 100,000 years Milankovi added up all the orbital wobbles and predicted that ice ages should occur in regular cycles - probably happening every hundred thousand years or so. Cause (5): Suns pacemaker
The Oil Drum cold hot 1000s of years before present Presenter notes: Now youll remember that in the 1960s, Nick Shackleton had figured out a way to see how the polar icecaps had contracted and expanded through time using heavy oxygen in microscopic marine animals. In 1976 Shackleton further showed that ice ages happened every 100,000 years just as Milankovic had predicted. Here was crucial evidence that wobbles in the Earths orbit around the Sun were acting like a sort of pacemaker, causing the planet to flip in and out of Ice Ages. In 1960s, deep sea records showed that Milankovi was right! The Earths climate had repeatedly blown hot and cold with ice age cycles happening every hundred thousand years just as Milankovi 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? Presenter notes: But one big question remained: Exactly how did changes in the amount of solar energy reaching the Earth trigger Ice Ages? So far, this is a question that scientists have been unable to answer. However, we have three good ideas. So far there are no firm answers but three good ideas Cause (7): Colour of the Poles
Absorbs energy: Warming 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 suns energy, so this would have caused further cooling, leading to an Ice Age. Presenter notes: The first idea concerns the colour of the poles. If the Earth started to cool down, we can imagine that green forests in the far north would eventually get replaced by white ice. Ice reflects back more of the suns energy so this would cause further cooling. In turn this would result in more ice at poles. We call this kind of process a positive feedback loop. Once the Earth starts to cool, changes lead to further cooling, and a downward spiral into an Ice Age. Reflects energy: Cooling en.wikipedia.org/wiki/Image:AntarcticaDomeCSnow.jpg Cause (8): Greenhouse Gases
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. NOAA Greenhouse Gas levels dropped during Ice Ages Presenter notes: A second idea is that changes in greenhouse gas levels in the atmosphere were to blame for the Ice Ages. The sun heats the Earth and the Earth re-radiates some of this heat. Greenhouse gases absorb this re-radiated heat keeping the Earth warm. Youll remember how scientists found air bubbles in polar ice cores. This tells us that the amount of greenhouse gas in the atmosphere dropped during Ice Ages. This would have sped up the cooling of the Earth. Last Ice Age = Low Greenhouse Gas Cause (9): Ocean Currents
Gulf 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 Presenter notes: A third idea is that ocean currents like the Gulf Stream were important. Today, this current carries heat from the equator and heats up the Arctic. If it wasnt for the Gulf Stream, Britain would have a cold climate like Newfoundland! If the Gulf Stream ever switched off for some reason, this would cool the Arctic further and increase the likelihood of an Ice Age. 800/le-gulf-stream.jpg Practical Exercise 2 The Day After Tomorrow?
Presenter notes: And that leads us nicely onto our next investigation. In this exercise we will watch the Hollywood blockbuster movie, The Day After Tomorrow (2004). This movie deals with the scenario weve just discussed, i.e. the idea that if the Gulf Stream switched off it would increase the likelihood of an Ice Age. But how realistic is the film? How much is fact and how much is fiction? You decide. commons.wikimedia.org/wiki/Image:Perito_Moreno_Glacier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG Ice Age Europe (1): Geography
20,000 years ago Europe was very different at the height of the Last Ice Age. Thick ice sheets in north Frozen tundra in centre Presenter notes: In this final section, we are going to explore what Europe was like at the height of the Last Ice Age about 20,000 years ago. At this time, northern Europe was covered by an ice sheet more than three kilometres thick. However, we will focus our attention on southern England, which evidence shows was a frozen and treeless tundra just south of the ice sheets. Conifer forests in south We will focus on the tundra region of southern England. Ice Age Europe (2): Coasts
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 sheet Presenter notes: With so much water locked up as ice, sea level was much lower at the height of the Last Ice Age. In fact you could have walked from Germany to England across land where the North Sea is today. Consequently, it was fairly easy for Ice Age animals and human hunters to migrate between Britain and Europe. Tundra Ice Age Europe (3): Plants
en.wikipedia.org/wiki/Mountain_Avens 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. Presenter notes: It was so cold in the Last Ice Age that almost no trees could survive in southern England. Evidence from fossil pollen show that the main plants were grasses and sedge in addition to a few stunted trees such as the arctic willow, dwarf birch and dwarf juniper. All these plants probably only grew a few centimetres high as they do today. They covered the landscape with a springy carpet of vegetation. We find pollen from one common flower, the mountain avens (Dryas), so this would have brought a bit of colour on the tundra landscape. The mountain avens (Dryas) was common in the Ice Age tundra Ice Age Europe (4): Mammals
commons.wikimedia.org/wiki/Image:Woolly_mammoth_siberian_tundra.jpg Presenter notes: Although cold and inhospitable, many large animals survived on the tundra of southern England. Best known is the woolly mammoth whose shaggy coat was well adapted to these harsh conditions. Some complete mammoths have even been found, deep frozen in the ice of Siberia. In fact there are several stories of explorers having eaten mammoth meat after stumbling over the frozen carcasses! Other animals that lived on the tundra included woolly rhinos, reindeer, horses, musk ox, and even lions and spotted hyaenas. Today we think of lions and hyaenas as exotic animals characteristic of the African savannas. However, this distribution is a result of human hunting and competition. Without humans, lions would be a normal part of the British fauna! 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: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. Presenter notes: Europe during the Last Ice Age was also the hunting ground of early humans like the Neanderthal Man. This is an extinct species of human whose fossil bones show a thickset body that was very well adapted to life on the ice. Neanderthals got wiped out near the end of the Last Ice Age. No one is quite sure why this happened. Maybe when modern humans arrived, they ate the Neanderthal foods and the Neanderthals couldnt compete. Although our brain sizes are similar in size, modern humans had the edge over Neanderthals because of cultural and social abilities (eg. fully developed speech, art, a more complex toolkit). This helped them to survive and thrive during the Last Ice Age when the Neanderthals failed. en.wikipedia.org/wiki/Image:Homo_sapiens_neanderthalensis.jpg Ice Age Europe (6): Our ancestors
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 Presenter notes: Fossil evidence shows that our modern human ancestors arrived in Europe right at the end of the Last Ice Age. They left spectacular artwork in caves that tell us what life was like at that time. The most famous cave art is in the Lascaux Cave in France and shows many of the animals which were hunted for food. Ice Age hunters also lived in southern Britain. Burial chambers have been found in South Wales and some cave art has even been found in Derbyshire recently. en.wikipedia.org/wiki/Lascaux Art in the Lascaux Cave, France Ice Age Europe (7): Melt water
en.wikipedia.org/wiki/Image:Gordale_scar_from_bottom.jpg wikimedia.org/wiki/Image:Malham_Cove.jpg ancient waterfall Presenter notes: As the Last Ice Age came to end about 14,000 years ago, huge volumes of melt waters flooded over northern Europe. In many part of England you can still see the effects of these catastrophe floods. For example in Derbyshire, the deep gorge at Goredale Scar was cut by floodwater. As this flowed downstream it formed a colossal waterfall at Malham Cove! Goredale Scar and Malham Cove in Derbyshire As the Last Ice Age came to an end, gorges and waterfalls were cut by melt water floods across northern Europe Ice Age Europe (8): Sea Level
As ice sheets melted, sea level rose by 120 metres reaching present levels about eight thousand years ago. Presenter notes: Another effect of the melting ice was to significantly raise sea level. Over a period of about seven thousand years, there is evidence from around the world that sea level rose by an amazing 120 metres (more than twice the height of Nelsons column). The English Channel and North Sea flooded and Britain became an island. Fishing boats trawling the North Sea bottom today occasionally find mammoth tusks left behind from the animals that used to graze on these Ice Age lands. en.wikipedia.org/wiki/Image:Post-Glacial_Sea_Level.png Ice Age Europe (9): Rebound
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. Presenter notes: The huge weight of the ice sheets over northern Britain pressed it down into the crust. When the ice completely melted, Britain started to rebound upwards, in much the same way that a rubber duck will bob back to the surface of a bath when released but much more slowly! We can observe the effects of this rebound in Scotland today. On the Isle of Arran we can find old sea caves which are now high and dry and well above sea level. This rebound is still going on today with Scotland rising by a few millimetres each year. Sea caves left high and dry on Arran The Ice Ages Presenter notes: So that brings us to the end of our exploration of the Ice Ages. Weve looked at how geologists first got an inkling that there had been an Ice Age in the recent past. Weve discussed what causes Ice Ages and weve explored what Europe was like at the height of the Last Ice Age. Its hard to imagine a thick ice sheet lying over the top of Manchester just 20,000 years ago. But what the ice age tells us is that climate can change dramatically over only a few hundred years. As we close, here are some questions to think about and discuss: So what about the Day after the Day After Tomorrow? Could the Earth continue to warm due to greenhouse gas emissions, and if so, what would this mean for the sea level of the UK? What would it mean for us? Or could Earths orbital wobble trigger another Ice Age in near future? as scientists thought was happening just 30 years ago. If so, what would this mean for the sea level and climate of the UK? What would it mean for us? NSA Howard Falcon-Lang