Why is plankton so important for life on Earth?

The answer

Phytoplankton are microscopic photosynthetic organisms that produce approximately 50% of all the oxygen in Earth's atmosphere, rivaling the contribution of all terrestrial forests combined. They form the base of nearly every marine food web, supporting everything from tiny zooplankton to the largest whales. Phytoplankton also play a critical role in the carbon cycle by absorbing an estimated 10 gigatons of carbon dioxide from the atmosphere each year. When they die, they sink to the deep ocean, effectively sequestering carbon in a process scientists call the biological pump.