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"Life" on Mars
History The idea of Martians is almost as old as the telescope. Early observers turned their gaze towards Mars and saw patches of coloration that changed with the seasons. People believed that this could be due to vegetation that was seasonal. Now we know that this is actually due to seasonal changes in the ice caps and dust patterns. The next big craze was started by Italian Giovanni Schiaparelli in 1877, when he observed grooves in Mars that he termed "canali," which directly translated means "channels." English Percival Lowell took a different approach and translated them to be "canals," and throughout the 1890's he built an observatory and mapped his canals. He believed that an intelligent Martian society realized that their planet was drying up, and in order to try to save failing crops, they had built an elaborate system of canals to bring water from the poles to warmer, drier equatorial regions. Even though this didn't make sense to many scientists at the time, people tend to be caught and stay hooked onto interesting bad science rather than boring good science*, and so a whole world believed in Martians. When Orson Wells broadcast H. G. Wells' (no relation) War of the Worlds to radio audiences on October 30, 1938, broad portions of the United States population were convinced that Earth faced a Martian invasion, and panicked. Thousands of science fiction stories were written about life on Mars, and pop culture embraced the idea, including the popular TV show with "Marvin the Martian." However, these fantasies were put to rest when, in 1965, Mariner 4 landed on Mars, and it photographed a dead, cratered planet, where the smallest feature of the photographs - the resolution - was a few hundred meters (a little less than half a mile). However, some of the pictures looked to show evidence of recent volcanic activity and water. July and September of 1976 brought Viking
1 and 2 to Mars. They landed, photographed their surroundings, and conducted
experiments
*This phrase is sinfully taken from my astronomy professor's, Prof. Christopher Mihos at Case Western Reserve University, web site for ASTR 221. Recent Discovery
Controversy The first question people want to know is if the rock is really from Mars. Yes, the rock is from Mars. A list of meteorites known to be from Mars is found at the bottom of the Asteroids page. Dating procedures have shown that the rock was formed approximately 4.6 billion years ago, and the organic chemicals about 3.6 to 4.0 billion years ago. Gases that were trapped inside are identical to what the Viking spacecraft found when they landed in 1976. The next question that many people ask is if there was any contamination from Earth biota. It has been shown that there has been no Earth contamination of the meteorite.
Two more pieces of data discount these as proof of life. The chemicals can to be formed by shocked rock that has been suddenly heated to 700 K (800 °F). Also, the "worms" are extremely tiny: They are 10-20 times smaller than the smallest "micro-fossils" from Earth. Being only 5 nm (only 500 times larger than most atoms), they are probably too small to support any nucleic acids (DNA or RNA) - the genetic building blocks of all life as we know it. As Carl Sagan said, "Extraordinary claims require extraordinary evidence," and that extraordinary evidence is not evident from Mars, at least not yet. Water and the Possibilities To sustain life, a planet must be the correct distance from a host star, have water, and have an atmosphere suitable for living organisms. At the current time, Mars is on the outer edge of being the correct distance from the sun. All of its water is frozen in its polar ice caps or under its soil, and its atmosphere is being blown away by solar winds. So, any current life is probably not able to be supported. It is possible that life may have flourished billions of years ago, but we will not know until scientists have studied the planet further. Some scientists believe there could be fossils in the ice caps or buried deep under the soil - the Vikings only examined the upper few centimeters (inches) of soil in a very limited locality. There is another meteorite which came from Mars that suggests that Mars had running water in the past (200-800 million years ago). Traces of a compound called "iddingsite," which is a mixture of clays and iron oxides, were found on the meteorite. Iddingsite only forms when there is running water, and radiocarbon dating shows that the iddingsite was on Mars when the compound formed. 
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to
try to verify or disprove life. They scooped up samples of the soil, gave them
nutrients and water, and looked for byproducts such as oxygen and CO2 (carbon
dioxide). The initial results were promising, but were later shown to be no
more than simple chemical reactions, and reproducible under similar conditions
in Earth laboratories. Strike two for Martians.
Then
the Viking Orbiter took the picture at the left (this has been cropped and edited)
of the "face" of Mars, taken from the Cyadonia region. Some people
took this to be proof of life on Mars (and the concept was made into a movie, Mission
to Mars). However, most scientists discount this, for when viewed under
different lighting conditions, it looks nothing like a face. Also, the 
In
1996, scientists began to study a rock that was jettisoned off of Mars 16,000,000
years ago and landed on Earth in Antarctica 13,000 years ago. On this rock, recovered
in 1988 and called Alan Hills 84001 (ALH84001 for short), the scientists found
small, worm-shaped structures called chondrules, which form when the rock is
subjected to climactic stresses. The scientists believe that the structures formed
billions of years ago when water seeped into the rock. In them, they found what
appeared to be fossilized worms, organic material, and another usually life-based
compound called "magnetite," which is formed by many Earth bacteria
in reaction to the magnetic field. They declared that this might be a form of
primitive Martian bacteria, proving life from Mars.
All
of the organic chemicals have been found throughout space, and so do not require
life to have been produced. The magnetite has been shown to be probably inorganic.
Also, Mars has no contiguous magnetic field, so there is no reason for the magnetite
to have been formed by biological interactions with it. As for the "worms," they
could easily be circular minerals that are being viewed edge-on.