Three feet down, he found what many people could find under their gardens: a cross-section of historical soils from pasture, through cropland, forest and steppe, and finally the dark clay that would once have been the bottom of an Arctic lake.

His point? When it comes to the natural world, there is no normal baseline. ‘At least five completely different sets of animals and plants have lived here during this extremely short space of time,’ he says. ‘The biological world has been turned on its head repeatedly since the end of the last ice age.’ Ecosystems everywhere are now being turned on their head again in what scientists are forecasting to be a sixth major extinction.

Despite the positive title, Thomas is quick to establish that a possible extinction event is no good thing, merely that it will create opportunities for other species to flourish. Just as the last five mass extinctions resulted in a rapid increase in biodiversity (the meteorite that wiped out the dinosaurs left the floor open for mammals and birds), the impact of mankind is making both winners and losers out of the natural world. ‘I do not wish to downplay the losses,’ he writes, ‘particularly in regions where major new land clearances are taking place. More vertebrate animal species have disappeared than new ones have formed. Yet new hybrid animals as well as plants are coming into existence and populating the Earth at a faster rate than ever before… we should also applaud the gains.’

It is an unconventional argument – but one that brings a new, optimistic angle to the conservation debate.

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