We can't see them in the water, but tiny organisms -- many of which are invisible to the unaided human eye -- make up 98 percent of the oceans' biomass and cause most of the biological activity there. They're found everywhere from the ocean surface to deep within rocks under the ocean floor. On the Summer Solstice on June 21, scientists all over the world participated in Ocean Sampling Day, an effort to collect samples and identify many of these life forms.
Above, this white sulfate material from a thermal vent in West Mata, a volcano near the Samoas in the Pacific, contains Epsilonproteobacteria.
PHOTOS: Small World Under the Sea