Hello, I'm Justin Rowlett. Welcome to the fifth and final episode of a Geochemical History

of Life on Earth, here on the BBC World Service. Over the last four episodes, we have

voidced through four billion years of evolution to understand how life shaped and mastered our planet's

chemistry and thrived in the process. In this final episode, we extend that journey into what some

geologists have dubbed the Anthropocene in honour of our own species because for better or worse,

the future of life on Earth is very much in our hands. It raises an uncomfortable question,

does the journey end here? Will the carbon dioxide that we're spewing into the atmosphere

overwhelm life on Earth and us with it? Or can we too learn to master our planet's chemistry

and take life another giant leap forwards in that journey?

Because let's be honest, life was doing just fine before we humans suddenly turned up.

The totality of life on the planet is creating and maintaining the conditions for its own flourishing.

Tim Lenton is a professor of climate change and Earth system science at Exeter University in the UK.

To demonstrate his point, he took us to some woodland near his office.

All around us here, life is mining the rocks underneath, there's sucking the carbon out of the

atmosphere, recycling all the nutrients, rounded around to support this intense productivity.

Tim's argument is that all life forms depend on each other. Without trees and plants,

there'd be no oxygen for us animals to breathe. Without tree roots and fungi, key nutrients

would remain locked up in the rocks. And without animals, fungi and bacteria, dead material would not

get recycled into the soil, ready to be taken up by the plants again. This idea that life on the

planet as a whole cooperates to sustain itself is known as the Gaia hypothesis, named after Gaia,

the Greek goddess of the Earth. But flourishing complex ecosystems like this woodland

are actually quite recent in Earth's history. They took almost four billion years to evolve,

...