Humans are warm blooded and can't be cold blooded because of the environment we live in. We can't sit still during the winter and soak up warmth from the sun.
Photosynthesising primary producers require sunlight. Therefore, in the ocean, phytoplankton would be concentrated within the surface layers of the ocean where the sunlight penetrates. Phytoplankton support a wide range of marine life: zooplankton feed on phytoplankton, which in turn support fish and so on.
Fossil fuel was non existent 2.5 billion years ago
