So, shipping is directly driving the climate crisis. Without shipping, we wouldn’t have coal moving from Australia to India and China, oil moving from the Middle East to China to be turned into plastics, or any of that. But thinking with the ocean also allows us to see history differently. It allows us to see that the environmental crisis didn’t start with the Industrial Revolution or after World War 2; instead, it has a much longer history that is intimately bound up with European colonialism and the systems of exploitation, slavery and violence it imposed on much of the world.

At the beginning of the book, you use the Arthur C Clarke quote: “How inappropriate to call this planet ‘Earth,’ when clearly it is ‘Ocean’.” What personal experiences drew you closer to that belief?

I grew up by the beach in Adelaide till I was 18. And then when I moved to Sydney, we lived in Bondi for a long time. In that way, the sea has been a huge part of my life. These days, I live a few suburbs away from it, but nearby is a big estuary. Again, when I was first working on the book, I went to the Cocos Islands, and we were staying on an uninhabited island that has a beach that Darwin writes about in the Voyage of the Beagle, which is now covered in plastic. It still is an incredibly beautiful place and while I was standing in the water, and birds were moving overhead, I could see tiny sharks swimming through the shallow water next to me, literally on the sand, half out of the water. I remember being deeply struck by the way that place was a living whole, with all these creatures and organisms bound together in incredibly complex ways.

The deeper darker parts of the ocean are often compared to space. Do you think that analogy holds?

I actually don’t. One of our problems with the deep ocean is that we think of it as this alien place. It is part of our world. The deep ocean is the largest environment on the planet, and it’s one we’re all connected to in quite profound ways. One of the most important involves the carbon cycle. The ocean is a massive carbon sink, and absorbs huge amounts of carbon dioxide, and a lot of that ends up in the deep ocean, locked away in sediments. And many of the current systems that drive the climate system also take place in the deep. So, the deep ocean is a fundamental part of the cycles that drive our planet’s systems. And that connects us to it in a really fundamental way. There is no part of the world that we can just give up on or think it doesn’t matter.

What’s horrifying to me about deep sea mining is that having wrecked every other environment on Earth, we’re charging willy-nilly to tear it out without any consideration about what that might do to the animals and the kind of ecosystems that are down there. On a hopeful note, if we are thinking of conquering Mars, we definitely can at least take care of our own planet in the right way. We can by trying to bring down some of the extremes of wealth and poverty and improve the status of women. There’s a level at which these things are actually about building a more sustainable world. By building a fairer world, you are letting everyone have a stake.

You also speak of oceans existing on different planets.

There were oceans on Mars and may have been on Venus. There are still oceans on many of the ice moons. And if there’s life in them, then that tells us something about life being something that is probably everywhere. I see there is a legitimate scientific impulse to try to understand where life comes from and whether there’s life in other places.

What kinds of intelligent life exist underwater, and what does that tell us about their evolution?

While writing about this, I discovered the different kinds of sensory apparatus a lot of fish and dolphins have. When the dolphins swim in a group, they can see and hear what the other dolphins can by picking up on their sonar. They have a communal sensory world, which completely altered my mind. I didn’t go in with any doubt that there are other animals that are extremely intelligent but you do become aware of how differently they perceive the world, and the degree to which that has shaped them.

In the book, I also posed the question about whether we can think our way into other animals’ worlds. Obviously, it’s not really possible to imagine what it’s like to see with sound or experience, or feel electricity. But even if you can’t get to the point of fully imagining or inhabiting such a different way of being, trying is important because it shifts your perspective. It forces you to think about everything in a tangible way, about there being different ways of being in the world. It gets you to let go and step outside of this box of being human.

The chapter on sound vividly brings with it the idea of a vibrant, alive world under the ocean…

When you go down into the water, it’s full of sound, of the voices of animals. You hear a kind of chorus, the clicking and whirrs of fish and other creatures. And particularly if you go somewhere like a coral reef or a kelp forest, you can hear the shrimp’s crackle. Sometimes, you can also hear whale songs.

Like, when you’re on land, you can see a long way but can’t hear very far. In water, it’s the other way around. You can’t see very far, but you can hear huge distances, so a whale can hear things happening hundreds of kilometers away. I was at a seminar 15 years ago, and I heard that in 10 years’ time, acoustic ecology would be the biggest thing in the world. And sure enough, it is now enormous. Now, one can know how healthy a reef is by recording it. It’s one of those places where you see technology coming into play because then you can start running all of this stuff through artificial intelligence, working out the details and analysing complex information.

How has technology helped in our relationship with the ocean?

That’s an interesting question. A specially trained beluga whale turned up with a camera harness in Sweden, which the Russians had been using to spy. So, you can see various forms of technology are used for things like homing on fish much more efficiently, which is helping to drive more and more overfishing. Again, in the fishing industry, people are using transponders and other technologies to help combat illegal fishing by tracking and monitoring boats. This has also enabled one to use technology to work out such activity to regulate it better.

It is not that positive things are not coming out of it. An interesting study was done last year where they used satellite data and machine learning to determine how much dark fishing and shipping activity was going on. And the answer is huge as fuel and other goods are getting moved.

Your coverage of colonialism and swimming was fascinating. You say white men would never freestyle, which was for the “inferior” races. Please tell us more.

We think of swimming as being natural, but in fact it’s highly cultural and its history is intimately bound up in race and power. From the time of the Romans, Europeans mostly didn’t swim, and even once they went back to the water in the 18th century, they only swam breaststroke. Exactly why isn’t really clear, but what is clear is that they regarded the overarm strokes that Africans and Native Americans and Pacific Islanders used as uncivilized, and often referred to it as Black or native swimming. You also see the ability to swim being used as a way to reinforce racial hierarchies. It’s grotesque.

Kanika Sharma is an independent journalist.