Class Notes 

Summary of Today's Topic's

In 1984 it was reported that a meteorite just found in the ice fields of Antarctica could possibly be from Mars. This meteorite was called ALH84001, for the Alan Hill region in which it was found. Researchers rushed to do tests to try and confirm this. Many things made scientists believe this was a Martian meteorite. The first indication was that the gases trapped inside the 'bubbles' of the rock were the composition of the Mars atmosphere. The ratio of Nitrogen-15 to Nitrogen-14 (Nitrogen-15 is an isotope of Nitrogen-14) was not like that of Earth, nor of chondrites but of Mars.The rock was also determined to be 4.5 billions years old. This would make it as old or older than rocks on the Earth. By the level of ice that it was found buried in in Antartica, we know that it had been on Earth for 13,000 years. Before that, it had been ejected from Mars 1.6-3.5 million years ago.

A famous article was written in 1996 that made three claims about the possibility of past fossilized life on Mars. The first of these claims is the polycyclic aromatic hydrocarbons (PAHs). These are simple hydrogen carbons on the surface and inside of the the rock. They are as old as the rock, so they cannot be from Earth or from the time the rock spent in space. These PAHs are a possible side effect of the decomposition or decay or living organisms. If this were the case, then it would stand to strengthen the idea not only of the meteorite coming from a planet, but of the meteorite coming from a planet featuring life. Since the rock, as far as science is able to tell, did not originate on earth and neither did its PAHs, this meteorite might be a proof of extraterrestrial existence. However, these hyrdocarbons can also form from combustion at a high temperature, which means that their presence on the meteorite is unable to prove or even hint at one way or another whether or not life has existed elsewhere.

The second claim was that some tube-like structures found in the meteorite were fossilized bacteria. These structures are less than 1/100th the size of a single human hair, half the size of the smallest Earth bacteria known at the time. One major argument skeptics utilized was the fact that the "bacteria" found within the rock were so miniscule that they were very likely something else, such as artifacts from the microscope. It was believed that bacteria that small simply do not exist on earth.  Then Kajounder claimed to have isolated nanobateria as small as 50 nanometers from blood and urine. Whether or not these particles are contamination from Earth or not is more or less impossible to tell at this stage.

The third claim for life on Mars were the globules of carbonate on the surface. These are formed when living things decay. These are older than the time the rock was on Earth, but still younger than the rock.  This statement led many to speculation that this was proof that there was life, but it was only speculation. There was still not enough proof for life by this.   Also, the globules were iron-rimmed, containing a magnetite shell around the carbonate minerals. Critics noted that the carbonate globules found on the surface of the rock could have been formed by an inorganic process, specifically a heat reaction.  All three of these can also be created inorganically, so their strength is in their occuring all at the same time.  It would be extremely rare for them all to be formed unorganically, more likely that it is evidence of an organic process, even though we cannot yet prove it definitively. 

This is an example of science at its limits, there is no definite way to win this argument because extrordinary claims require extraordinary evidence.  The best answer that could be found would be if scientists were able to definitively determine the temperature of Mars at the time in which the meteorites were on the surface.  Lacking that, and possibly even with that information, there is no way that either side could win this argument.  There are many assumptions that researchers and critics are making regarding the search for life using the meteorites as evidence and they include: the possiblility of nanobacteria existing or not existing in the critics case that small, they are assuming that the nanobacteria in the meteorite are similar to those on Earth, and that none of the nanobacteria found are due to terrestrial contamination.

These tests of for evidence of organic processes and life on this metorite, have only created assumptions of whether life exists. These tests and "new" findings haven't given the debate any proof or support in regards to either side of the debate. They have only reinforced the opinions of the scientists who debate whether or not life has existed upon Mars. These scientists agree on the age and origin; however they heatedily disagree on the formation of the elements of the rock that are tested.

Primary Sources

http://upload.wikimedia.org/wikipedia/commons/c/c4/ALH84001.jpg (Image of ALH 84001)

 Polycyclic Aromatic Hydrocarbon example

Key Terms