Justin Rowlatt explores what was the original solar energy revolution – harnessing the sun’s rays to grow food. Some 10,000 years ago our ancestors began to till the soil, producing the energy surpluses needed to feed the first cities and civilisations. Growing crops was gruelling work, as Justin discovers at Butser Ancient Farm, when he tries to till some soil himself with a replica Stone Age mattock. But what first prompted our ancestors to take up such an arduous way of life in the first place?