BBC | How Earth Made Us | Episode 2: Water

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Aired January 26, 2010 on BBC Two

Professor Iain Stewart explores the complex history of our relationship with water as he continues his look at how geology, geography and climate have influenced human history. Visiting iconic and spectacular locations in Iceland, the Middle East, the Sahara and India, Iain explains how control over water has been central to human existence, and discovers how different civilisations have struggled to adapt to the constant changes in the distribution of this vital resource.

Starting his journey in one of the driest places on Earth, the Sahara desert, Iain discovers remarkable engravings in the rock dating back more than 6,000 years. These engravings of giraffes, elephants and crocodiles signify that this desert was once a very different place, a place where water flowed and people made a home. But the dramatic drying of the Sahara shows that water is constantly on the move around our planet.

The programme traces the cycle of fresh water which humans have come to depend on. From the ocean, it evaporates to form clouds, then falls as rain into rivers. Some is stored as ice while another portion sinks below the planet's surface to become groundwater. Water is constantly moving through this cycle, but the cycle itself also changes over time. Iain discusses one such change which happened towards the end of the last ice age, when a final burst of cold caused the ice to expand. As moisture was drawn out of the atmosphere and turned to ice, this led to a vicious drought in the Middle East.

Coping with the lack – or abundance – of water has driven some of the key advances of human civilisation. In early history the need for reliable water supplies led early farmers to settle near rivers, but as humans spread across the planet they learned to exploit the vagaries of the water cycle in many different ways. Adapting to the water cycle has meant the difference between success and failure for many civilisations.

Now, in the 21st century, man's ability to harvest, transport and store water has improved vastly. But the human population has also grown and this combination has placed a great strain on the finite amount of water on our planet. This has led to water becoming a continual source of conflict, a battle which will only intensify as the demand for water increases in the coming years.

(Thanks to AnonyKai)