Support In early 2003, scientists detected methane in the atmosphere of Mars. Support Methane is a fragile compound that falls apart when hit by the ultraviolet radiation in sunlight. So Conclusion any methane in the Martian atmosphere must have been released into the atmosphere relatively recently.
The author concludes that any methane in the Martian atmosphere must have been released into the atmosphere only very recently.
Why?
Because methane falls apart when hit by UV radiation in sunlight.
(The author’s thinking that if we detect methane in the Martian atmosphere, then it must not have been hit by UV radiation yet. Otherwise, we wouldn’t be able to detect it. And the author further believes that if it hasn’t been hit by UV radiation yet, the methane must have only been around for a short time period.)
The author assumes that once methane falls apart, it would no longer be detectable.
The author assumes that methane in the Martian atmosphere will be exposed to UV radiation at some point in time. (This is why the author thinks the fact we can detect methane in the Martian atmosphere implies that the methane hasn’t been around for long — if it were around for a long time, the author thinks it would eventually be hit by UV rays and no longer be detectable.)
The argument relies on the assumption that
Mars had no methane in its atmosphere prior to 2003
Not necessary, because even if there were methane in Martian atmosphere prior to 2003, that methane could have fallen apart from UV rays. The author’s argument isn’t undermined if there was methane in the atmosphere 1,000 years ago or 1 million years ago, for example; what matters is whether the methane detected in 2003 has been around for a long time.
all methane in the Martian atmosphere is eventually exposed to sunlight
Necessary, because if it were not true — if SOME methane in the Martian atmosphere is NOT eventually exposed to sunlight — then the methane that we detected in 2003 might have been around for a very long time, because it didn’t fall apart from being exposed to UV rays.
methane cannot be detected until it has started to fall apart
Not necessary, because even if methane CAN be detected even before it has started to fall apart, that’s consistent with the author’s reasoning. The author thinks that the methane we detected has not yet fallen apart.
the methane that the scientists detected had been exposed to ultraviolet radiation
Not necessary, because even if the methane that was detected in 2003 had NOT been exposed to UV rays, that’s consistent with the author’s reasoning. The author thinks that the methane hasn’t fallen apart yet because it hasn’t been exposed to UV rays. This is why we were able to detect it.
methane in Earth's atmosphere does not fall apart as a result of exposure to ultraviolet radiation
Not necessary, because even if methane in Earth’s atmosphere DOES fall apart as a result of exposure to UV rays, that’s consistent with the author’s reasoning. The author believes that on Mars, if UV rays hit methane, the methane will fall apart.
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