This high-resolution scanning electron microscope image shows an unusual tube-like structural form that is less than 1/100th the width of a human hair in size found in meteorite ALH84001, a meteorite believed to be of Martian origin. Although this structure is not part of the research published in the Aug. 16 issue of the journal Science, it is located in a similar carbonate glob in the meteorite. This structure will be the subject of future investigations that could confirm whether or not it is fossil evidence of primitive life on Mars 3.6 billion years ago (text and photo courtesy NASA).
On August 7, 1996, NASA announced a startling discovery by examining a meteorite that originated on Mars, they found what they believe is evidence for a primitive form of life that may have existed on Mars 3.6 billion years ago. More work needs to be done to confirm this preliminary result, and many scientists remain unconvinced by the present evidence. But if this preliminary result is confirmed, if the structures inside the meteorite turn out to be fossil evidence for cellular organisms, then some important steps can be taken.
First, we would need to launch a mission to Mars, manned or unmanned, to secure and return to earth core samples that might provide evidence for or against DNA as the organizing scheme for the Mars life form. Having accomplished the return of a biological sample and determined the presence or absence of DNA, we are then faced with a quandary.
If the Mars life form is not based on DNA, it supports the hypothesis that life is a likely outcome for a planet with the correct temperature range, atmospheric pressure, liquid water, and sufficient time with these conditions. This would be a very important finding two planets with different histories, temperatures, atmospheric makeups and surface gravity, both producing life through random processes life based on different models, but life nevertheless.
We could use this result to reinforce the theory that life is common in the universe. This single data point, the existence of life of a different form on our sister planet, would greatly aid the theory that life may be a likely event in a reasonably wide range of planetary conditions. This finding would re-energize our search for evidence of alien civilizations.
But if the Mars life form is based on DNA, this is an equally interesting result, for a different reason because of the peculiar and ad hoc nature of DNA, and the number of equally viable alternatives to its specific structure, this outcome would strongly argue for a common origin for life on Earth and Mars.
It is hard to imagine two independent processes producing a mechanism such as DNA, especially if the two DNA forms turn out to be alike in their essential characteristics. It is much more likely that the two planets somehow shared some early organisms.
This conclusion leads to three likely hypotheses for DNA sharing:
1. Earth's DNA got to Mars.
2. Mars' DNA got to Earth.
3. Both Mars and Earth were seeded by some unknown third source.
The third of these alternatives has existed as a theory for some time. It is called "Directed Panspermia" it proposes that all life originated from some extraterrestrial source, and (in some forms of the theory) that life was placed on earth for a reason. This theory has everything going for it except plausibility and evidence.
The first of these alternatives (Earth to Mars) suffers from two problems. One, the Mars sample is 3.6 billion years old, earlier than any direct fossil evidence for life on earth. Two, Earth's atmospheric pressure prevents an incoming meteorite or asteroid from throwing surface materials entirely out of the atmosphere and into interplanetary space. There is evidence that Earth's atmosphere has had similarly high pressures for a long time period. Thus, it is not obvious how Earth's genetic material could get into interplanetary space.
The second alternative (Mars to Earth) is the most likely. Mars may have developed life in an early era of high atmospheric pressure, relatively high surface temperatures and liquid water. There is abundant evidence for all these characteristics except conclusive evidence for life.
In this hypothesis, around 3.5 billion years ago Mars' atmospheric pressure began to drop, and established life forms continued to exist only below the surface in pockets of liquid water. Then a meteorite or asteroid impacted on Mars' surface, expelling a large amount of material from the surface into interplanetary space carrying viable organisms with it.
The final step in this theory is that some of the Martian surface material fell into Earth's early oceans, and either successfully competed with, or provided, Earth's first cellular organisms.
This theory is consistent with the relative age and conditions of both Earth and Mars, and it is consistent with the age of the NASA sample, which may, with further work, show that organisms existed on Mars at a time, 3.6 billion years ago, before there is firm fossil evidence for life on Earth.
Here are some findings that would be fatal to this hypothesis:
1. If there is firm evidence that Mars' atmospheric pressure remained high until relatively recently, it would be hard to imagine how genetic material could leave the surface of Mars in time to provide Earth with its first DNA.
2. If it turns out that Earth's and Mars' cellular life forms are based on different principles, this theory has no purpose and can be set aside.
3. If the ongoing work with the Mars meteorites shows that there are no cellular structures inside the teasingly shaped cylinders seen in news photographs, that would also make this theory unnecessary.
If all these dominoes fall, however
if it turns out that there was early Martian cellular life based on
a familiar form of DNA, then it may be that we are all descended from an
ancient Martian cellular life form.
Credits and Biographical note: Paul Lutus has a wide background in engineering and science. He designed part of the NASA Space Shuttle, then began to develop computer software. His best-known program was "Apple Writer," an early word processor. In research and articles he has explored such topics as computer mathematics and graphics, and in 1985 he was named Scientist of the Year by the Oregon Academy of Science.
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