99% of Earth’s biomass is estimated to be on land, with only 1% in the oceans.

However, Earth’s biomass is mostly plants. And the average terrestrial plant is huge—a 2-ton tree that could live for a century. Whereas the average marine plant is tiny—a single-celled organism that might live just a few weeks.

That said, about three-quarters of animals, by biomass, live in the sea. That’s because the oceans are incredibly rich with tiny shrimp-like creatures. Antarctic krill alone make up almost 400 million tons of biomass.

But what’s really amazing about life in the ocean is how much we don’t know.

Scientists recently estimated that there are almost 9 million species of plants and animals on Earth. About 2.2 million of those are in the oceans—but only 10% of those are cataloged.

That’s right: by these recent estimates, over 90% of ocean species are unknown to science.

This correlates well with seafloor samples brought up from the deep. In them, about 90% of the species we find were previously unknown.

That may be about to change. The UN has declared the 2020s the Decade of Ocean Science. There are many projects underway to catalog species and map the ocean floor.

But with 2 million species yet to discover, it could take a thousand years to catalog them all …

Which makes it a very exciting new frontier for scientists.