Ufologists claim that the U.S. government is conspiring to keep secret alien spacecraft technology. Troubled medical patients have told psychologists about their alleged abductions by mysterious bulb-headed ETs.
While this writer is a flying saucer and "close encounter" skeptic, there are lifeforms living on the Earth that beg the question: "What exactly is an extraterrestrial?"
For example, could some unusually rugged microscopic lifeforms found on Earth have arrived on this planet from elsewhere? And if they evolved on Earth, why do they exhibit survival traits for environments not found anywhere on the Earth?
Several microscopic critters alive today defy conventional ideas about the survivability of terrestrial life in space-
Let's take a look at a funny looking microscopic tardigrade, commonly called the water piglet or water bear.
Tardigrades were discovered in pond water samples by Johann Goeze in 1773. Goeze called them Gleiner Wasserb r, a German term for Little Water Bear.
Indeed, tardigrades look like miniature, cartoon bears; they are water animals which live their lives in and around bodies of water.
The Latin name tardigrada means "slow walker"-these six-legged critters have a gait that looks like an animated Disney bear's walk. Of course water bears aren't anywhere near the size of mammalian bears we're familiar with; the biggest Gleiner Wasserb r is only 1.5 mm in length.
If we didn't know tardigrades were terrestrial creatures, we might take them to be tiny extraterrestrial visitors that hitched a ride to Earth on an extrasolar meteorite.
Tardigrades are what biologists call polyextremophiles-that is, they can live in extreme environments that would otherwise kill other animals. In Russian experiments, tradigrades have been found to survive temperatures close to absolute zero; they also survive temperatures up to 300 F.
In other experiments, tardigrades waddled happily through a radiation bath 1,000 times more deadly than an atomic bomb blast. Also, tardigardes discovered in 100-year-old dessicated mud deposits were reanimated and brought back to life by researchers.