New and exciting discoveries in the earth’s past ice age
DURING the summer of 2008, workers excavating Ground Zero in Lower Manhattan dug right down to the bedrock. There, they found something unexpected: a huge pothole more than 10 metres deep, the crevices around it crammed with stones of several different kinds of rock. The consulting geologist immediately recognised these features. The stones had been carried there from many miles away by a glacier that had ground across the bedrock. At some point, a swirling torrent of glacial meltwater had carved out the pothole.
From potholes in New York City to forests beneath the sea, evidence of the time ice dominated the world is all around us. The last great ice age began around 120,000 years ago. One massive ice sheet, more than 3 kilometres thick in places, grew in fits and starts until it covered almost all of Canada and stretched down as far as Manhattan. Another spread across most of Siberia, northern Europe and Britain, stopping just short of what is now London. Elsewhere many smaller ice sheets and glaciers grew, vast areas turned into tundra and deserts expanded as the planet became drier.
With so much ice on land, sea level was 120 metres lower than it is today. Britain and Ireland were part of mainland Europe. Florida was twice the size it is now, with Tampa stranded far from the coast. Australia, Tasmania and New Guinea were all part of a single land mass called Sahul. The planet was barely recognisable.
Then, 20,000 years ago, a great thaw began. Over the following 10,000 years, the average global temperature rose by 3.5 °C and most of the ice melted. Rising seas swallowed up low-lying areas such as the English Channel and North Sea, forcing our ancestors to abandon many settlements. So what drove this dramatic transformation of the planet? Continue reading