An ice age, is a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a longterm ice age, individual pulses of cold climate are termed "glacial periods" and intermittent warm periods are called "interglacials".
• In 1840, Louis Agassiz observed unique 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.
Parallel marks show former level of an ice-dammed lake
Glen Roy, Scotland
• Agassiz amassed more evidence from landforms and boulder clays to support his idea of a Great Ice Age in recent times.
• 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.
• 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.
Annual layers in ice
When the Last Ice Age was at its maximum, ice sheets covered much of Europe and North America. So what actually caused it?
Milutin Milanković (1879-1958) 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
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.
• In 1960s, deep sea records showed that Milanković was right!
• The Earth’s climate had repeatedly blown hot and cold with ice age cycles happening every hundred thousand years just as Milanković had predicted.
Greenhouse Gas levels dropped during Ice Ages
• 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.
• Some scientists believe 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
Much of the world’s water from seas and oceans got frozen. As a result , sea level dropped Places that had been under water become dry land Many plants and animals adapt to these changes but many died
These ice ages have been punctuated by Interglacials, short -warm periods of time, however our current interglacial has already lasted 12000 years, thank to GLOBAL WARMING.
The next ice age is more than 15,000 years away, according to evidence from an Antarctic ice core, the deepest and oldest ever extracted. The core gives us a 740,000-year record of the planet's climate, including the past eight ice ages, and interglacials in between. The core was more than 3 km long and measured to be 740,000 years old at its farthest end. The core gives a picture of the Earth's cycles of warm and cold, reflected in the different thicknesses of ice that fell on Antarctica as snow.