Palladium metal has one unique property: Hydrogen can filter through it. Thus, it was a crucial component of the Viking landers' GC-MS (gas chromatograph-mass spectrometer) experiments. The gas chromatograph which separates out volatile substances and the mass spectrometer which detects ions were divided by a palladium separator. The function of the palladium was to allow organic molecules transported by the hydrogen "carrier gas" (but nothing else) to pass from the gas chromatograph to the mass spectrometer.
All three Viking lander biology experiments indicated the presence of life within the Martian soil. However, because the GC-MS analysis showed no evidence of organic molecules, most scientists concluded that the first three tests had been false positives and, regrettably, there was no life on Mars.
Alas, the experiment was flawed. Palladium is "poisoned" by sulfur, an element abundant in the Martian soil. The sulfur was heated and released by the chromatograph's oven, after which nothing was able to pass through the palladium separator. Which means that instead of having one true reading and three false positives, the tests resulted in three true readings and one false negative.
There was life on Mars.
As we all found out in 2008 when a soil sample scooped up from the Martian surface by a NASA robot probe was returned directly to Earth without undergoing quarantine at Space Station Alpha.
The scrappy Martian microbes, used to a harsh, resource-poor environment, ripped through Earth's ecosphere like a slum kid who abruptly finds himself transported to a finishing school for pantywaists. Human beings, fortunately, were not directly vulnerable to any of the alien microorganisms.
Algae, unfortunately, were.
Algae were formerly responsible for something like ninety percent of the world's oxygen production. When they died, the props were knocked out from under almost all Terrestrial plant and animal life. Outside of our sealed habitats, only the Martian invaders remain.
Which is why it's so important that you always check your oxygen tanks before leaving the house.
© 2002 by Michael Swanwick and SCIFI.COM.