Oceans make up more than 99% of the Earth’s habitats by volume — yet less than 20% of them have been explored. Some even say it’s easier to send astronauts into space than it is to reach the ocean floor. Only a handful of people have ever reached the deepest part of the ocean - known as the Challenger Deep in the Mariana Trench in the Pacific Ocean. So, why is it so difficult to get there? And what new tech is helping us uncover the ocean’s secrets?

The BBC’s Climate and Science correspondent Georgina Rannard explains why we know so little about what’s going on in the deepest parts of the ocean and some of the discoveries that have been made about this mysterious part of our world.

Archive courtesy of British Pathé.

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