'Well, there is one hint – and it's so terrifying that we don't like to talk about it. Have you heard of Nova Scorpio?'

'I don't believe so.'

'Stars go nova all the time, of course – and this wasn't a particularly impressive one. But before it blew up, N Scorp was known to have several planets.'

'Inhabited?'

'Absolutely no way of telling; radio searches had picked up nothing. And here's the nightmare...'

'Luckily, the automatic Nova Patrol caught the event at the very beginning. And it didn't start at the star. One of the planets detonated first, and then triggered its sun.'

'My Gah... sorry, go on.'

'You see the point. It's impossible for a planet to go nova – except in one way.'

'I once read a sick joke in a science-fiction novel – "supernovae are industrial accidents".'

'It wasn't a supernova – but that may be no joke. The most widely accepted theory is that someone else had been tapping vacuum energy – and had lost control.'

'Or it could have been a war.'

'Just as bad; we'll probably never know. But as our own civilization depends on the same energy source, you can understand why N Scorp sometimes gives us nightmares.'

'And we only had melting nuclear reactors to worry about!'

'Not any longer, thank Deus. But I really wanted to tell you more about TMA ZERO's discovery, because it marked a turning point in human history.'

'Finding TMA ONE on the Moon was a big enough shock, but five hundred years later there was a worse one. And it was much nearer home – in every sense of the word. Down there in Africa.'

8 – Return to Olduvai

The Leakeys, Dr Stephen Del Marco often told himself, would never have recognized this place, even though it's barely a dozen kilometres from where Louis and Mary, five centuries ago, dug up the bones of our first ancestors. Global warming, and the Little Ice Age (truncated by miracles of heroic technology) had transformed the landscape, and completely altered its biota. Oaks and pine trees were still fighting it out, to see which would survive the changes in climatic fortune.