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Geologists define time by looking at major shifts in the Earth’s system, and chop up the planet’s timeline into Periods and Epochs – you may have heard of the Jurassic, Carboniferous and Pleistocene. We have been in the Holocene epoch for almost 12,000 years, since the last great Ice Age. Now it is time to enter a new epoch – and its personal this time – it has been coined the ‘Anthropocene’, the Age of Man because humans are influencing the very fabric of the planet. But there is some debate over exactly when it started. Scientists like nice, neatly defined markers – like the chemical signature left by the meteorite strike that wiped out the dinosaurs – called a ‘golden spike’. They also require long-lasting changes to the Earth.

There are two good candidates according to ecologist, Dr Simon Lewis, and physical geographer, professor Mark Maslin from University College London. They are 1964, the year after the Nuclear Test Ban Treaty was put into force, giving us a golden spike of radionucleotides in various deposits. But their favourite is 1610, when the collision of the New and Old Worlds a century earlier, were first felt globally. The spread of diseases, like smallpox, from the Old to the New World killed off over 50 million people, who were mostly farmers. This meant a wholesale cessation in agriculture in South America, leading to the native forests re-growing, using up carbon dioxide in the atmosphere and resulting, in 1610, with a dip in the atmospheric gas which can be seen in ice cores.

Origin of the Brain
Scientists disagree over the origin of the brain. Some say it evolved in just one common ancestor which was a forerunner of all the brains in the animal kingdom, others think it developed more than once and separately in different creatures.

The Application of Physics
The American Physical Society’s meetings are always good for some unusual applications of physics, this time the stickiness of mussels, how the eye sees colour and crowd behaviour come under the spotlight.

(Photo: The crew of Apollo 17 took this photograph of Earth © NASA/Getty Images)