NASA had sent two Viking landers to Mars in the 1970s. This mission gave some very important insights about Mars along with some very intriguing results. One of the experiments hinted about the detection of life on the Red Planet. The evidence at that time was not found to be fully conclusive however Dr Gilbert Levin, one of the experimenters says that he is highly convinced that we had found extraterrestrial life at that time. His findings are reported in the Scientific American journal.
The experiment named Labeled Release (LR) had a simple setup. A drop of diluted nutrients was added to the Martian soil sample which was tagged with a radioactive carbon isotope. If there were lifeforms emitting carbon dioxide on the surface of Mars, the radioactive tag would have been released hence getting detected by the experiment.
The experiment was conducted by both of the Viking landers. One collected a sample exposed to sunlight and the other collected one from beneath a rock. Both of these experiments reported detection. This was again repeated after a week by using the same sample however there was no detection at that point. Hence the results were deemed inconclusive by Levin and partner Dr Patricia Ann Straat.
Since the Viking Experiments failed to detect life, NASA concluded that the detection by LR was nothing but a result of chemical reactions. However the results of the experiment have been under assessment over the last few years and scientists have argued that this might be the first detection of alien life. This along with the results of several other experiments have made Mars a strong candidate for sustaining life.
Levin mentions in his paper that there is no evidence against the possibility of life on the Red Planet. Studies have also shown that few terrestrial microbes could grow on Mars.
Levin is correct in suggesting that the possibility of life cannot be ignored although we cannot take lack of proper evidence as proof for existence. He mentions that efforts should be made for life detection experiments in the next mission to Mars. An improved version of the LR experiment with an ability to detect chiral metabolism have been proposed by Levin and his partner scientist to be sent for confirming the existence of life. Living things can distinguish between left and right handed organic molecules which cannot be done by non-biological chemical reactions.
Existence of life on Mars has been debated for several years now, there has been no concrete proof yet but we might be nearing towards some solid evidence.