Once upon a time, scientists routinely found life in places where it wasn’t supposed to exist. That doesn’t happen anymore, and not because the pace of discovery has slowed. If anything, it’s accelerated. It’s simply become clear that life can exist almost anywhere on Earth.

After 3 billion years of evolution, life has flowed into every last nook and cranny, from the bottom of the sea to the upper edge of the stratosphere. From blazing heat and freezing cold to pure acidity and atomic bomb-caliber radiation, there’s seemingly no stress so great that some bug can’t handle it.

This gallery highlights a few particularly tough species of bacteria and archaea, a lesser-appreciated but equally-vast branch of the organismal tree. Until the late 1970s, archaea was lumped in with bacteria, a confusion that speaks to the embryonic state of human microbial knowledge. Less than 1 percent of Earth’s microorganisms have been identified, and most of those won’t even grow in a lab.

In some cases, the bugs are labeled as being uniquely durable, but the labels almost certainly won’t stick. Hardly a month passes without some newly characterized species setting a new microbial benchmark. Indeed, the very concept of species might not apply. Bacteria and archaea exchange genes “horizontally,” without the need for reproduction. It’s as if, while encountering someone on the street, you could trade for whatever genes came in handy at the time. This fungibility makes a mockery of old-fashioned, animal-based notions of species, and some microbiologists want to abandon the concept altogether.

Speaking of the common gut bacteria Escherichia coli, biology pioneer Lynn Margulis once said, “If you put a particular plasmid into E. coli, all of a sudden you have Klebsiella and not E. coli. You’ve changed not only the species, but the genus. It’s like changing a person to a chimpanzee. Can you imagine doing that, putting a chimpanzee in the refrigerator, and getting him out the next morning, and now he’s a person?”

It’s pretty hard to imagine, and the idea of microbes as an Earth-spanning ur-organism might take some getting used to. In the meantime, here are some examples of life’s awesome adaptability.

Image: WikiMedia Commons/U.S. National Parks Service

Update, 11:30am ET: The post originally mischaracterized archaea as being far less complicated than bacteria, and bacteria as possessing a cell nucleus — neither of which is true. They differ from each other profoundly, but not in ways that lend themselves to such hierarchical judgments.

One thing bacteria and archaea have in common, however, is the lack of a nucleus or other membrane-bound cellular substructures. Only eukaryotic cells, which compose the bodies of plants, animals and fungi, have such structures.

Herminiimonas glaciei, recovered from ice found two miles beneath a Greenland glacier is one of the smallest microbes ever found. With extra-long, tail-like flagella, it’s perfectly suited to moving through tiny veins in the ice.

Described in a paper published last week in the International Journal of Systematic and Evolutionary Microbiology, H. glaciei was resuscitated by University of Pennsylvania researchers after an estimated 120,000 years of dormancy. Last June, the same research team described another glacier-recovered, lab-revived microbe, Chryseobacterium greenlandensis. They think it could be a couple of million years old.

Image: Society for General Microbiology (left), Dave Apple/Flickr (right)

Pyrodictium abyssi, discovered in 1979 on the nutrient-rich edges of deep-sea volcanic vents, are the original extremophile all-star. In addition to atmospheric pressure that could pancake a submarine, they can withstand temperatures well above the boiling point of water.

The flat, irregular disk-shaped P. abyssi accumulates in networks of hollow, tube-shaped structures called cannulae that are structurally resistant to heat.

Image: Microbe Wiki (left), NOAA (right)

Deinococcus peraridilitoris is the lesser-known cousin of Deinococcus radiodurans, dubbed the toughest bacterium on Earth by the Guinness Book of World Records. Found in 2003 in soil from the Atacama desert, a region of Chile so dry and desolate that NASA uses it for Mars simulations, it can withstand cold, vacuum, drought and radiation. Key to its survival are multiple copies of its genome; when one is damaged, the necessary sections can be copied from the other.

Image: Public Library of Science (left), NASA (As no images of D. peraridilitoris could be found, D. radiodurans is pictured.)

Haloquadratum walsbyi was found in a salt flat near the Red Sea, an environment so saline that, as phrased in the Snail’s Tale blog, “you and I and just about every other organism on Earth would shrivel up into a lifeless bag of desiccated stuff.” In response, the square and ultra-flat archaeon has the highest surface-to-volume ratio of any creature on Earth. You can’t get much more shriveled than that.

Image: H. Bolhuis, University of Groningen (left), Kevin Jones/Flickr (right)

Halobacterium NRC-1 is the most radiation-resistant organism on Earth, capable of withstanding some 18,000 grays of radiation. (Just 10 grays are required to kill a human.) That nearly doubles the mark set by D. radiodurans, which was originally discovered in the 1950’s as the sole survivor of irradiated meat. Like D. radiodurans and D. peraridilitoris, it’s especially good at repairing its own DNA.

Image: NASA (left), U.S. Department of Energy (right)

Ferroplasma acidophilum can grow in a pH of zero — conditions that make sulfuric acid look like mineral water. Found in the toxic outflow of a California gold mine, it uses iron as the central structural element of nearly all its proteins.

Image: Helmholtz Centre for Infection Research (left), NASA (right)

Desulforudis audaxviator is perhaps the one truly singular microbe. Every other known organism exists in a system in which at least some nutrients are provided by other creatures. But not D. audaxviator, which was discovered in a South African mine shaft, two miles beneath Earth’s surface and entirely alone. Using radioactivity from uranium-containing rocks as energy, it can harvest or metabolize every nutrient it needs from surrounding rock and gas — the world’s only known single-species ecosystem.

Image: J. Craig Venter Institute (left), Unforth/Flickr (right)