It happens sometimes that the material itself carries things you have not fully planned. The footage has its own right, its own life, its own vibrancy and energy in it.

I always felt completely confident - it's like in a feature film, knowing your principle character is extremely well-cast. I had that same confidence in Clive [Oppenheimer].

You are confronted with abysses of time that are, in a way, unfathomable. You see a painting in charcoal of raindeer and it was left unfinished and somebody else finished it. But through radio carbon dating we know that the next one completed the painting 5,000 years later. You're just blown away by the notion of passage of time. We have no relationship to that kind of depth of time.

Your film is like your children. You might want a child with certain qualities, but you are never going to get the exact specification right. The film has a privilege to live its own life and develop its own character. To suppress this is dangerous. It is an approach that works the other way too: sometimes the footage has amazing qualities that you did not expect.

Netflix knew I was going to North Korea and Ethiopia and Iceland. They saw the film and liked it and that was that.

Without dreams we would be cows in a field, and I don't want to live like that. I live my life or I end my life with this project.

Of course, you do not do any research: you have to go there and do your film. It's not that I would travel there before without a camera and spend half a year on one of those volcanoes and then come back with a camera. You have to have some sort of a clear mindset.