Life on Mars
In early August 1996, a very provocative announcement was made by a respected group of scientists, an announcement that caused an uproar amongst astrobiologists. On August 7, these scientists revealed that they had discovered evidence that supports the existence of microscopic life on Mars some 3.6 billion years ago.† The story resulted in an amazing media sensation, capturing the attention of a global audience and evoking skepticism amongst even the most optimistic scientists.† Now, almost a decade later, we continue to look back on this story as a striking example of how the process of science unfolds.†
The story truly began in 1984 when scientists first
collected the meteorite catalogued as ALH84001, now commonly known as the
The discovery of meteorite ALH84001 didnít receive much attention until after scientists made the claim that the ancient Mars rock contains evidence of past life from Mars.† The evidence seemed straightforward.† Scientists identified features inside the rock that they proposed were ancient fossilized microorganisms.† They also found organic matter, which is often a byproduct of life.† Finally, scientists magnetite, a mineral that is common on Earth and can be associated with life.†
The announcement that past life on Mars had been discovered caused people all around the world to take notice.† But why was there such a strong public response and interest in the possible discovery of life on another planet?† Is it because humans have been wondering for several centuries about the uniqueness of life on Earth?† What is our role in the universe?† Is it possible that there are other worlds that have environments similar to Earth and life forms like ours?† Is life on Earth an example of the inevitable consequences of cosmic evolution, or is it a unique cosmic accident?† These questions are the basis of a broad intellectual inquisition that has lasted for several centuries.† It makes sense, then, that the proposition that evidence for life beyond Earth had been discovered would capture the attention of the global community and would subsequently be subject to scrutiny by the scientific community.
The actual claim that ALH84001 contained irrefutable evidence for ancient Martian life was less than compelling to some scientists.† The rock did not contain confirmed fossils of microbes or direct imprints of complex organisms.† Several of the molecules contained in the meteorite that were originally thought to be a byproduct of life were reconsidered once it was learned that frequently form without life.† The biggest problem, biologists noted, was that the proposed "fossilized life forms" were smaller than any known microbes on Earth, only 1/1000 the diameter of a human hair.† They were concerned about whether or not a structure so small could contain enough genetic material to constitute life.† In addition to skeptical biologists, some chemists were not convinced that the organic material found within the rock truly had a biotic origin.† They contended that the material could have been created through purely non-living chemical processes.† Other scientists doubted whether any life form could have survived the extreme temperatures to which the rock may have been exposed upon ejection from Mars.† Ever since the announcement in 1996, scientists have continued to evaluate and re-evaluate the evidence supporting and refuting the claim that we have received evidence for life from Mars.† The controversy encompassing ALH84001 is still unresolved and remains an area of debate amongst scientists even now.
How can the ALH84001 controversy help illustrate the process of science?† Well, what is the process of science?† How do we come to "know" something about the natural world around us?† We as humans have not always believed that there are physical explanations for the diverse phenomena in our world.† For example, we now believe that solar eclipses are caused when the Moon passes in front of the Sun.† We have rejected the notion that eclipses express the displeasure of Sun gods, as some ancient cultures believed.† Now when we encounter a phenomenon we do not understand or discover unique situations, we endeavor to study then through a logical, systematic method.† This method includes making observations, posing questions, gathering evidence, and analyzing all the information we have collected.† The knowledge that we gain is not necessarily absolute.† However, it is the process of evaluating information and drawing conclusions that can lead us to know something meaningful about our world.† We may never come to a solid conclusion about the presence of past life from Mars in ALH84001, but we can certainly come to learn more about life and its mysteries during the process of investigation.†