Clandestine Colossus

Recent research conducted over a span of 10 years by 1200 scientists from 52 countries (that's one hell of a collaboration!) has discovered a vast subterranean ecosystem that is almost beyond belief in its size and mass. It is in the form of microbes that likely weigh somewhere between 10 and 25 billion tonnes. That's several hundred times the combined weight of all of us human beings! Just try to wrap your head around the fact that all these tiny, one-celled critters outweigh Homo sapiens several hundred times over—and they are all below the planet's surface, out of sight! We like to believe that we surface creatures are what it's all about, as we walk, swim, and fly across the crust of Earth.

These microbes live in conditions that we deem hostile to life, yet they prosper in extremely hot locations (up to 122^o C or 250^o F, like inside an oven), with no light, under intense pressures, and with minuscule nutrition. Some of their life spans are measured in geologic times, their pace is so slowed down. They are alive and do metabolize, but use such little energy that they live for millennia and appear to be in stasis. Their movement can be measured in centuries—triggered by tectonic plate shifts, earthquakes, or volcanic eruptions. At first glance, they would appear not even to be alive. We already know that microbes—bacteria and archaea—dominate on the Earth's surface, but these findings show that less than 30% of all the planet's microbes live on the surface—the vast majority is hidden.

The scientists who made this discovery did so by creating boreholes up to 5 km (3 miles) deep. The latest types of microscopes were also employed. Since the underground microbes are buried so deeply, they live in a pristine world—as yet uncontaminated by humans. As we foul the planet's surface, they continue to live beyond the reach (so far) of our harmful technologies.

These findings raise some intriguing questions about life on Earth—and possibly elsewhere. Where and how did life begin on our planet? Did it originate at the surface and later migrate downward or did it start at depths and later move upwards? What do we make of critters whose metabolism is so slow that they endure for millennia? Maybe these microbes could be identified by this study as living, because all life on Earth has similar properties and the scientists recognized some familiar features. 
 
What might this discovery say about examining possible life forms on another planet or even moons of our solar system, where life there may be of a very different chemistry or live a much slower existence—so slow that we may not even recognize them as living? If humans continue their reckless ways, the environment on Earth's surface may become unlivable for most species. If that happens, are these underground microbes—this clandestine colossus—waiting to surface one day and reinhabit our planet?

There are undoubtedly many other questions that could arise, as we continue to explore and characterize this vast underground ecosystem. We keep making discoveries that broaden our understanding of the various forms and conditions of life. It is opening us up to possibilities that we recently had no idea existed. What new discoveries await us—here on Earth or out there?

Covert Critters

We critters who live on the surface of planet Earth can become quite provincial about our kind—by being quite unaware of the many life forms that live underground. For example, people see other people as the most important critters on the planet. That's probably true for other surface species. We see each other, interact with each other, and conclude that's about all there is to it.

But there's a vast biosphere that is hidden from us, just below our feet. It might as well be covert. All of us surface critters live in an extremely thin layer on the surface of the planet. The atmosphere and the exposed land are like the thin skin of an apple—there's so much more below the skin. For example, subsurface fresh water—existing down to many miles—has a volume of about 100 times that of surface fresh water. Subsurface life has a mass of some 20 times all that lives in the ocean and makes up about one-third of all the planet's biomass. That's pretty impressive!

Never experiencing the sun, subsurface life cannot depend on photosynthesis, as must all surface life. Photosynthesis in plants enables them to manufacture sugars for themselves, as well as all other critters of the light, who eat plants or other plant-eating creatures. How do the covert critters survive without light and its resultant photosynthetic sugars? They feed on dissolved minerals in the water, as well as raw hydrogen. Thus they are reliant on biochemical reactions, which are much less efficient than photosynthesis. As a result, subsurface life exists in the slow lane. Underground microbes (and most life down there is in the form of microbes) may divide once every thousand years or so. Contrast that to surface E.coli, which divide every 20 minutes! This is a pace of life some 30 million times faster!

Moreover, underground life-forms are much tougher than their surface cousins. In 2003 the space shuttle Columbia broke up during reentry into the atmosphere. Aboard Columbia was a biological experiment on nematodes—very hardy, underground tiny worms. They survived the fiery explosion and they survived the 25 mile plunge to the ground where, a few weeks later—when they were subsequently located—they were reproducing!

Earth's subsurface life-forms are closer in character and metabolism to the earliest kinds of life on the planet, thus recent discoveries of these covert critters are helping scientists to understand how those deep ancestral creatures survived and thrived. Our expanding comprehension of the limits of metabolism of life on Earth is preparing us to better understand what kinds of life (if any) we'll find on Mars, or Jupiter's moon Europa, or Saturn's moon Enceladus—most all of which is likely to be subsurface, if it exists.

These findings make us wonder about what other kinds of critters we'll yet find on (or under) Earth. With each passing year we expand the limits of what we know to be life.