Overview

Until recently, it was generally held that life, specfically microbial life, occupied no deeper than several tens of meters into the Earth's crust. Similarly, the temperature range that constrained life was thought to be relatively narrow.

Both these ideas have been overturned by new discoveries of bacteria inhabiting minute gaps in rock kilometers deep and living in geysers and boiling sulfur pools.

As the envelope for biology keeps widening, the prospects for finding life, current or past, on our likeliest extraterrestrial candidates, Mars and Europa, continue to improve.

Chart of Extremophiles

from Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies
-- Space Studies Board (SSB)

from Rock-eating microbes found nearly a mile beneath the ocean floor
-- exoSci.com, 8/14/98

It used to be thought that the biosphere descended some several tens of meters into the Earth's crust and stopped there. That was before they started analysing the rock cores that are brought routinely when we drill for oil and the like. At first, the finding of bacteria in cores from as much as kilometers deep was discounted - explained as contamination by surface bacteria. But careful, sterile handling of core samples - for example, kept in chambers of inert gas and carefully guarded against any exposure to the surface environment - has shown that bacteria and even higher multicellular protozoa (feeding on the bacteria) live to great depths in the interior of the Earth.

Many of the bacteria species consume organic material that has been resorbed into the Earth's interior: this material is, for example, the source of our oil and gas reserves. These species metabolize with oxygen and are thus not so different, in this metabolic-functional sense, from surface bacteria.

But other species, living in the tiniest of gaps in deep granitic and basaltic formations, have nothing to do at all with oxygen and metabolize hydrogen. Some scientists have suggested that these species are relic of the earliest forms of life on the planet, when there was no oxygen atmosphere - remember, our oxygen atmosphere is actually a byproduct of photosynthetic life.

It has been suggested that the amount of "biomass" inside the earth is as great or even greater than that in what we traditionally think of as the biosphere. Think about it: in some sense, the dominant lifeform on (or rather, in and on) planet Earth is the lowly bacterium.

Kinda makes you humble, doesn't it...

"Negative findings... are as important as positive ones in their importance to our understanding of the processes that determine the limits to life."
-- Mike Purdy, LeXeN program, National Science Foundation

Critical reaction thought to support underground microbes now considered unlikely
"This is an important step forward in our continuing efforts to understand the processes that sustain life deep beneath the earth's surface"
-- exosci.com, 8/14/98

Rock-Eating Microbes
Scientists at Oregon State University have discovered evidence of rock-eating microbes living nearly a mile beneath the ocean floor in conditions which suggest similar life could exist on Mars or other planets.

Microbial fossils were found in abundant quantities in miles of core samples taken during various research projects by the Ocean Drilling Program in the Pacific, Atlantic and Indian oceans...

Where the basalt was glassy, having quickly been cooled by seawater, the scientists found a series of tracks and trails. "Whenever we looked at those tracks for DNA, we found it" ...

Rock-eating microbes found nearly a mile beneath the ocean floor
-- exosci.com, 8/14/98

One of the surprises about thermophiliac bacteria is that varieties have been found that not only survive but actually thrive in boiling water. The upper limit on temperature to date is 239 degrees fahrenheit, some 27 degrees above the boiling point of water! Interestingly, these heat-loving "hyperthermic" microbes can only grow at the elevated temperatures.

Biochemistry
... have adapted their biochemistry to function at these high temperatures ... A number of enzymes has been purified from hyperthermophiles and as expected, most have a thermal transition temperature above the boiling point of water ...Based on these properties, it is often concluded that hyperthermophilic proteins are very rigid.

On the other hand, protein flexibility is essential for catalysis, thus rigid proteins might be poor catalysts even at higher temperatures. It is therefore surprising that the catalytic power of enzymes from hyperthermophiles is equal or sometimes higher than that of their mesophylic counterparts. ... the mechanisms by which this is achieved are essentially unknown.

from Redox Enzymology
-- Netherlands

Upper Temperature Limits for Growth of Various Organisms

from Life at High Temperatures
-- University of Wisconsin-Madison Department of Bacteriology

Hypertherms and the Origin of Life
Preliminary data from Zimbabwe2 and elsewhere suggest that these end members are a hydrothermal component (similar to modern black smoker fluids) and a seawater component (surprisingly similar to that in modern seawater). This inference tallies with rRNA evidence that early life was hyperthermophile.

from The Composition of Archean Oceans from the Geochemistry of Archean Sediments
-- University of London, Department of Geology

Some scientists suggest that life on Earth may have originated during the planet's earliest periods, some three billion or more years ago. At that time, the so-called Hadean Eon, Earth was indeed like "Hades" - with minimal atmosphere composed of poisonous gases from continuous volcanic activity, with radioactive heating at levels much higher than now, with regular meteoric bombardment searing the surface of the planet. It would have been microorganisms similar to the thermophiles that could have survived in such an environment. If this is true, then the thermophiles could be the forerunners of all life on Earth.

Ocean 540 Project Proposal: Geologic Constraints on Subsurface Microorganisms
"While Gold (1992) has speculated upon the nature and extent of a "deep, hot biosphere" within the Earth, and Deming and Baross (1993) have proffered upper temperature and pressure limits to the growth of hyperthermophilic microorganisms collected from deep-sea hydrothermal vent systems, the degree to which heat flux and geochemical processes constrain life within the oceanic crust has yet to be thoroughly examined."
-- School of Oceanography, University of Washington

Halophiles

The exact chemical explanation for the extreme salt tolerance of these bacteria, and their need for salinity at least three to four times that of sea water, is very complicated. The cells themselves contain a very high internal salt concentration (primarily potassium and sodium), equal to or higher than their environment, otherwise, they would be rapidly dehydrated (plasmolyzed) in the brine. It has also been shown that the highly saline environment is essential for normal enzyme function within the cells, and to maintain the fragile protein coating or "wall" around the delicate cell membrane. In fact, if the salt concentration drops too low, the outer protein "wall" actually dissolves and the inner cell membrane disintegrates, thus destroying the cell (Larsen, 1967).

Halobacteria can thrive in concentrated brine nine times the salinity of sea water, and can even remain alive in dry salt crystals for years.

Halobacteria are placed in the "Archaebacteria," a group of unusual bacteria that survive under some of the most extreme conditions on earth. In fact, some biologists feel that these bacteria should be placed in their own Kingdom Archaebacteria, separate from the Kingdom Monera that contains most of the true bacteria. Heat-loving (thermophilic) Archaebacteria have been found thousands of feet deep at the bottom of the ocean, near steam vents where the water temperature is three times that of boiling water. They can live in this black world of boiling water without oxygen. It has been suggested that if any bacteria could survive on the surface of Mars, it might be a form similar to the Archaebacteria.

Other halophiles:

• Dunaliella & Stephanoptera , unicellular green algae, thrive in water with 33 percent dissolved salts ... unlike the halobacteria, a high osmotic concentration within the cells of Dunaliella is produced by a very high concentration of glycerol molecules instead of salt ions.
• Dangeardinella saltitrix, a smaller unicellular green alga ..like the halobacteria it can survive in solid salt crust.

from Why Owens Lake Is Red!
-- DesertUSA.com

Other
Extremophiles

The bacteria absorb trace amounts of manganese and iron from the atmosphere and precipitate it as a black layer of manganese oxide or reddish iron oxide on the rock surfaces. This thin layer also includes cemented clay particles which help to shield the bacteria against desiccation, extreme heat and intense solar radiation.

Several genera of bacteria are known to produce desert varnish, including Metallogenium and Pedomicrobium.

All living systems require the vital energy molecule ATP (adenosine triphosphate) in order to function. In our cells ATP is constantly produced within microscopic bodies called mitochondria. As electrons flow along the membranes of our mitochondria, molecules of ATP are generated. The electrons come from the breakdown (oxidation) of glucose from our diet. Although varnish bacteria do not have mitochondria, they do have a similar inner membrane structure through which electrons flow to generate ATP.

However, in varnish bacteria the electrons come from the oxidation of manganese and iron rather than glucose.

These miniature rock dwellers have survived for countless centuries in some of the most seemingly inhospitable environments on earth and may represent some of the oldest living colonial life forms.

from Desert Varnish On Rocks And Boulders
-- DesertUSA.com

Surviving in Space
In November, 1969, the Surveyor 3 spacecraft's microorganisms were recovered from inside its camera that was brought back to Earth under sterile conditions by the Apollo 12 crew. The 50-100 organisms survived launch, space vacuum, 3 years of radiation exposure, deep-freeze at an average temperature of only 20 degrees above absolute zero, and no nutrient, water or energy source.

from Earth microbes on the moon
"Apollo 12 Commander Pete Conrad: 'I always thought the most significant thing that we ever found on the whole...Moon was that little bacteria who came back and lived and nobody ever said [anything] about it.' "
-- Space Science News, Nasa Marshall Space Flight Center

Radioactive-loving
Can you believe it? There are bacteria that can live *inside* nuclear reactors.

Deinococcus radiodurans
"The members of the family Deinococcaceae have the distinctive feature of being the most radiation-resistant of vegetative cells. Certain strains have survived as much as 5 Mrad of gamma radiation. An important component of this radiation resistance is the ability to repair damage to chromosomal DNA."
-- National Center for Genome Resources

Rock-loving
... in 1961 a friend, an oil geologist, brought him a piece of limestone with a green substance inside. The geologist thought the green coloring was some form of copper, but chemists said it was not. “Perhaps,” he suggested, “it is something biological.” Friedmann could hardly believe his eyes. He scraped off a sample, whisked it to the nearest microscope, and saw algae.

Porous rock, Friedmann soon realized, is a better habitat for a microbe than parched desert soil. A rock can store water in its pores, and because it is often translucent, it can admit sunlight, allowing photosynthesis, yet filtering the extremes of strong light that kill microorganisms in the desert.

Once he knew where to look, Friedmann found endoliths everywhere. “These mountains,” he says, pointing to a photograph of the Negev on his wall, “look absolutely barren.” Indeed, as you scan it you see no trees or shrubs, not a blade of grass, not even a lichenous rock. It looks as dead as, say, the surface of Mars. “But inside, the hills are practically covered by a green layer.” Only a millimeter beneath the hard, rocky surface, he found, the desert slopes were alive.

from Looking for Life in All the Wrong Places
-- Discover Magazine

Too Bizarre for Words (Bizarro-philes?)
Microbes that live in a bath of sulfuric acid which is produced as an intermediate product of their own metabolism.

Clues to Life in Cave of Goo
"So where one would expect to find no life, there is much life indeed, thriving in an environment that eventually would kill other creatures. Pisarowicz and Hose believe their discoveries could offer powerful implications in the search for life on Mars"
-- ABCNews.com

Totally wierd! Clearly the forms of life defy our notions of neat and tidy.

Maybe the odd scientific result will be if we go to these other planets and *don't* find life?

Links

Rock-eating microbes found nearly a mile beneath the ocean floor
"Scientists at Oregon State University have discovered evidence of rock-eating microbes living nearly a mile beneath the ocean floor in conditions which suggest similar life could exist on Mars or other planets."
-- exosci.com, 8/14/98

Life Underground
"Recent research on deep rocks on Earth has shown that bacteria can live kilometers beneath the surface. Some bacteria live on nothing but rock and water, extracting energy from chemical reactions rather than from sunlight. Life on Earth, and perhaps on Mars and even other planetary bodies may have originated in such strange environments, and if so, the subsurface of water-rich planets, asteroids, and satellites might be home to a rich diversity of microorganisms. "
-- Planetary Science Research Discoveries 12/21/96

Rock-eating microbes found nearly a mile beneath the ocean floor
"Scientists at Oregon State University have discovered evidence of rock-eating microbes living nearly a mile beneath the ocean floor in conditions which suggest similar life could exist on Mars or other planets."
-- exoSci.com, 8/14/98

Critical reaction thought to support underground microbes now considered unlikely
"It had been generally accepted by scientists that hydrogen gas produced from rock could provide energy to support the growth of microorganisms living below Earth's surface, says U. Mass. microbiologist Derek Lovley. The hydrogen was thought to be produced when basalt, a common form of rock, reacts with water. However, a research team led by Lovley has found that this concept is incorrect."
-- exoSci.com, 8/14/98

Microbes Deep Inside the Earth
"Recently discovered microorganisms that dwell within the earth's crust could reveal clues to the origin of life."
-- Scientific American, 10/96

Researchers Seek Origin of Deep Subsurface Bacteria
"Life on our planet may have evolved first at depth, then migrated to the surface as the environment became more tolerable. If this is so, the study of deep, subsurface microbial communities may provide another key to exploring our distant past. Ironically, these tiny creatures also may carry keys to our future." (DOE Subsurface Science Program)
-- American Geophysical Union

Microbes in Rocks
"Researchers ... announced that they had found bacteria living inside core samples of shale and sandstone taken from depths ranging from two to nearly five hundred meters underground."
-- Japan High-Tech Satellite Network, 6/12/97

The Biosphere Below

The intraterrestrials
"The existence of a whole new biosphere within the Earth inevitably raises the stakes in the search for life elsewhere in the Universe. Around 3·8 billion years ago, when Earth was very young, it already harboured substantial populations of bacteria. The youthful planet was still being bombarded from space by giant chunks of rock and exposed to killing ultraviolet radiation ... Parkes and many others believe that while the surface died, life retreated to the deep biosphere until conditions improved on the outside.
-- New Scientist Magazine, 3/7/98

Microbes thrive far below ground
"Even organisms living near seafloor vents rely indirectly on the oxygen supplied by photosynthesis..."
-- ScienceNewsOnline, 3/29/97

Looking for Life in All the Wrong Places
"Cryptoendoliths... They are Earth's pariahs: microbes that just barely survive, in the least hospitable places on the planet. And yet they, or something much like them, could seed the universe with life."
-- Discover Magazine

Geomicrobiology Research Group
Research and publications
-- Department of Geosciences, Princeton University

Earth interior - geology

Earth's Interior & Plate Tectonics
The Earth's Interior - The Lithosphere & Plate Tectonics - Oceanic Lithosphere - Continental - Lithosphere - Plate Tectonics - References
-- Views of the Solar System

Geology: Water--400 Miles Below Earth's Surface
"His discovery suggests that Earth's mantle contains tons of water at depths where most geologists believed water couldn't possibly exist."
-- Discover Magazine, 5/98

Subcrustal Ice Earth Model
"Could the earth contain a subcrustal ice layer? Jupiter's largest satellites, Ganymede and Callisto, have water/ice mantles and rocky cores ..."
-- Private website

General Geyser Information
links
-- Private website

The Geyser Page
general information
-- Western Kentucky University

Thermophiles & other extremophiles

Thermus aquaticus
"... biologists thought life would not tolerate temperatures anywhere near 80 degrees Celsius. But Brock kept finding bacteria, so he kept on looking. Eventually, he found organisms that could live and reproduce near the temperature of boiling water -- 100 C.
-- The Why Files

Extremophiles
"About 30 years ago scientists thought that life could only exist in a very limited number of environments. However, many interesting bacteria have been found nearly everywhere we look."
-- Suite101.com

Life at High Temperatures
From booklet published by Yellowstone Association for Natural Science, History & Education, Inc.
-- University of Wisconsin-Madison Department of Bacteriology

Clues to Life in Cave of Goo
"So where one would expect to find no life, there is much life indeed, thriving in an environment that eventually would kill other creatures. Pisarowicz and Hose believe their discoveries could offer powerful implications in the search for life on Mars"
-- ABCNews.com

Extremophiles: Life Under Extreme Conditions
Technical journal.
-- Springer Science

Microbial life in extreme dry regions (Death Valley)
"One of NASA's key reaearch goals concerns the question of life on Mars. There is considerable geological evidence that there once was liquid water on the surface of Mars. However, through time the planet evolved to become cold and dry. From a microbial perspective, the key biological stress is not the low temperatures, but the arid climate. To understand how life can survive in dry conditions we have been engaged in studies of microbial life in extreme dry regions of the Earth."
-- Center for Mars Exploration, NASA

Extremophiles
"Imagine diving into a refreshingly cool swimming pool. Now, think instead of plowing into water that is boiling or near freezing. Or consider jumping into vinegar, household ammonia or concentrated brine. The leap would be disastrous for a person. Yet many microorganisms make their home in such forbidding environments."
-- Scientific American, 4/97

Extremophiles'98 Congress
"The Congress, which will be composed of 7 sessions including the new fields of exobiology, subgroundmicrobiology and genomes, will focus on both fundamental and applied studies of microorganisms that are adapted to live in extreme environments."
-- Japan Marine Science and Technology Center

Why Owens Lake Is Red!
"One of nature's most remarkable biological phenomena is the reddish coloration of salt lakes and playas. Here is the explanation, known heretofore only to a handful of desert naturalists!"
-- DesertUSA.com

Desert Varnish On Rocks And Boulders
"These miniature rock dwellers have survived for countless centuries in some of the most seemingly inhospitable environments on earth and may represent some of the oldest living colonial life forms."
-- DesertUSA.com

Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies
"As advances in the biological and planetary sciences enable a shift from mere observation to active exploration of the solar system, space missions are increasingly likely to collect samples from planetary satellites and small solar system bodies and return them to Earth for study."
-- Space Studies Board (SSB)

Chart of Extremophiles
-- see above

UMass Microbiologist Focuses on Iron-Eating Bacteria
"... seven species of hyperthermophiles... could use iron to metabolize its food. This lends weight to the theory that iron was essential for the growth of early life on Earth ...All of the hyperthermophiles converted iron oxide to the magnetic mineral, magnetite, during their growth on iron ...geologists have found large accumulations of magnetite on early Earth ... magnetite found deep below the Earth's surface and in a Martian meteorite has been thought to provide evidence for the possibility of life existing in these extreme environments."
-- Astronet, private website, Netherlands

Hyperthermophilic Organisms
-- Argonne National Laboratory

Archaebacteria--A Life Form On Mars?
"The Three Major Types Of Archaebacteria:1. Methanogens (methane producers) --responsible for swamp gas. 2. Extreme Thermophiles--live in hot springs and black smokers. 3. Extreme Halophiles--live in saturated brine and salt crust."
-- Private website