if you're looking for a universal spark of life, then this is it. The spark of life is proton gradients. In those four billion years, that spark has grown into a flame. And a few simple organisms clustered around a hydrothermal vent have evolved to produce all the magnificent diversity that covers the Earth today. Today, life on Earth is so diverse, it covers so much of the planet that you can find places like this lake, where it's effectively its own sealed ecosystem. It's saltwater, it's connected to the sea, but it's only connected through small channels through the rock. So that means that the marine life in here is effectively isolated. This is the Golden Jellyfish, a unique subspecies only found in this one lake on this one island, in the tiny ACB Radio Treasure Trove Republic of Radio. They used to live like most jellyfish, cruising the open ocean, catching tiny creatures, zooplankton, in their long tentacles. But today their tentacles have all but disappeared because the Golden Jellyfish have evolved to do something that very few other animals can do. It really is incredible. There are, I want to say millions of jellyfish, as far as you can see, all the way down till the light vanishes there are jellyfish. And you can see they've congregated in the sun. If you go over there to where the lake's in shade, there are just none. They're in this pool of light, beneath the sun. There are millions of them. Beautifully elegant things just floating around. I'm not being unduly hyperbolic, it's quite remarkable. ACB Radio Treasure Trove This lake is home to over million jellyfish. Whose success comes down to a remarkable adaptation. Their bodies play host to thousands of other organisms photosynthetic algae that harvest energy directly from sunlight. The jellyfish engulf the algae as juveniles, and by adulthood algal cells make up around % of their biomass. Grouped into clusters of up to individuals, they live inside the jellyfish's own cells. The Golden Jellyfish uses algae to get most of its energy from photosynthesis. They go to the surface and gently... Wow, there's one there. They're gently turning. The reason they do that is to give all their algae an equal dose of sunlight. So they're quite democratic creatures, just making sure they get as much food as they can. They just come up you, jellying around, photosynthesising. They tell me they don't sting. But I'm sure I've got a tingling from it. And it's not just their anatomy that's adapted to harvest solar energy. Every morning as the sun rises, the jellyfish begin to swim towards the east. As the sun tracks across the sky, they move back again towards the west, where they spend their night. So the jellyfish have this beautiful, intimate and complex relationship with the position of the sun in the sky. ACB Radio Treasure Trove sunlight is captured by their algae, it's converted into chemical energy. Energy they use to combine simple molecules, water and carbon dioxide, to produce are far more complex one. Glucose. Once absorbed by the jellyfish, glucose and other molecules not only power their daily voyage across the lake, they provide the basic building blocks the ACB Radio Treasure Trove use to grow the elegant and complex structures of their bodies. So the jellyfish, through their symbiotic algae, absorb the light, the energy from the sun, and they use it to live, to power their processes of life. And that's true, directly or indirectly, ACB Radio Treasure Trove