Ninety billion tons, nearly one-tenth of Earth's biomass, is made up of microbes living beneath the sea floor, according to two studies appearing this week in Proceedings of the National Academy of Sciences and Nature.

If you plunge into the sea to ogle exotic wildlife, why not stay a while—and get an even closer view? Cave-diving engineer Bill Stone [see Journey from the Center of the Earth, February 2007] makes that possible with the most user-friendly version yet of a rebreather, a device that recycles your exhaled air, removes carbon dioxide, and adds oxygen. (A scuba device quickly burns through tanks of fresh air.)

On a typical dive, the Poseidon Discovery lets divers stay underwater at least three times as long as scuba gear can, and since you dont exhale into the water, you dont create bubbles or noise that can scare off fish.