The following is an excerpt from a BBC broadcast of the Reith Lectures 2010. The Reith Lectures are a series of annual radio lectures held in the UK on significant contemporary issues, delivered by "leading figures from the relevant fields".
And I’ll conclude with a cosmic vignette. Suppose some aliens had been watching our planet from afar for its entire history. What would they have seen?
Over nearly all that immense time, 45 million centuries, Earth’s appearance would have altered very gradually. Continents drifted; the ice cover waxed and waned; successive species emerged, evolved and became extinct. But in just a tiny sliver of the Earth’s history, the last one millionth part, patterns of vegetation altered at an accelerating rate. This signalled the growing impact of humans and the advent of agriculture.
Then, in just one century, came other changes. The amount of carbon dioxide in the air began to rise anomalously fast. The planet became an intense submitter of radio waves - the output from TV, cellphones and radar transmissions. And something else unprecedented happened: small projectiles, launched from the planet’s surface, escaped the biosphere completely. Some were propelled into orbits around the Earth; some journeyed to the moon and planets.
If they understood astrophysics, the aliens could predict that the biosphere would face doom in a few billion years when our sun flares up and dies. But could they have predicted this sudden fever less than halfway through the Earth’s life? And if they continued to keep watch, what might these hypothetical aliens witness in the next hundred years in this unique century?
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