The world's oldest plant lives off Ibiza

Under the sea, between Ibiza and Formentera, stretches a meadow of Posidonia. It looks like seaweed, but it isn't: it's a full-blown marine plant, with roots, flowers and fruit, that blooms underwater just as an almond tree does on land.

The astonishing part is its age. Genetic studies reckon this meadow may have been growing for around 100,000 years, cloning itself endlessly from the same original plant. It would be one of the oldest living things on the planet.

It also does enormous quiet work: it cleans the water, holds the sand on the beaches in place, and stores carbon like few other ecosystems.

So when the water in the Balearics looks impossibly clear, thank a plant that was already there when humans hadn't yet left Africa.