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.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: William Lee Adams Producers: Baldeep Chahal, Julia Ross-Roy, Emily Horler and Emilia Jansson Video Journalist: Baldeep Chahal Editor: Verity Wilde

Across cultures, weddings are usually a big event. Lots of us look forward to dressing up and dancing the night away with the person we love — but what if you kept all the festivities and got rid of the romance? Well, some young people in China are doing exactly that, by looking online for a ‘marriage buddy’. They pretend to be together to please their families, but aren’t actually legally married. So, why are they willing to go to such lengths to meet societal expectations? And how does it all work?

Wanqing Zhang from the BBC’s Global China Unit talks us through the process — and explains the pressure put on young people in China to tie the knot. And we hear from Linda, a young woman in China who tells us why she’s decided to find a marriage buddy.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Iqra Farooq Producers: Chelsea Coates, Mora Morrison and Maria-Clara Montoya Video Journalist: Baldeep Chahal and Jem Westgate Editor: Julia Ross-Roy

Loneliness is a feeling lots of us face from time to time… and it might be more common than you think. A new study from the World Health Organisation suggests that between 2014 and 2023, one in six of us were feeling lonely - and teenage girls reported feeling this way the most. Apps like Bumble BFF or Meetup and social media groups dedicated to meeting new people are also on the rise. So why are so many of us feeling lonely? And what can you do to feel more connected?

BBC journalist Emilia Jansson takes us on a friendship date, sharing her experience of using social media to make new friends and helping us to unpack the data on loneliness. We also hear from teenagers around the world who describe when they’ve felt lonely. And Dr Laurie Santos, a psychologist professor at Yale University in the US, tells us her top tips for tackling loneliness.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Iqra Farooq Producers: Mora Morrison and Chelsea Coates Editor: Emily Horler