odysseus2000 wrote:ursaminortaur wrote:
If the life on Mars was transmitted to Mars from Earth then tons of similar transmissions have already occurred as meteoroids blasted off Mars have travelled to the Earth and another one could happen tomorrow. Hence any samples returned from Mars would be unlikely to bring anything Earth hasn't already seen before. Also viruses and bacteria on Earth are rarely able to cross species barriers so something from Mars would not be likely to survive on Earth unless it had made a very short round trip and happened to meet whatever it had once infected on Earth before it started that round trip.
Life which had developed totally separately from that on Earth would likely find infecting Earth life even harder. Viruses in particular would find infecting Earth life forms challenging since they would have by chance to firstly have some means of getting inside cells and then secondly have some means of taking over the infected cell's machinery and using it to produce more of this virus. Neither is likely if the virus has never come across Earth cells before.
Wasn’t the data from the Vikings lander that suggested bacteria, indicative, if true, that what ever was on mars had similar life needs to Earth bacteria? That could imply contamination before the experiment or if it was a real signal that was seen in two experiments about 3000 miles apart lots of bacteria on Mars that shares at least some characteristics with Earth life.
The LR test simply provided any Martian organisms with a nutrient rich broth with radioactive labelling of nutrients. The organisms didn't need to be able to infect other organisms in order to obtain those nutrients.
https://blogs.scientificamerican.com/observations/im-convinced-we-found-evidence-of-life-on-mars-in-the-1970s/
NASA’s reservation against a direct search for microorganisms ignores the simplicity of the task accomplished by Louis Pasteur in 1864. He allowed microbes to contaminate a hay-infusion broth, after which bubbles of their expired gas appeared. Prior to containing living microorganisms, no bubbles appeared. (Pasteur had earlier determinted that heating, or pasteurizing, such a substance would kill the microbes.) This elegantly simple test, updated to substitute modern microbial nutrients with the hay-infusion products in Pasteur’s, is in daily use by health authorities around the world to examine potable water. Billions of people are thus protected against microbial pathogens.
This standard test, in essence, was the LR test on Mars, modified by the addition of several nutrients thought to broaden the prospects for success with alien organisms, and the tagging of the nutrients with radioactive carbon. These enhancements made the LR sensitive to the very low microbial populations postulated for Mars, should any be there, and reduced the time for detection of terrestrial microorganisms to about one hour. But on Mars, each LR experiment continued for seven days. A heat control, similar to Pasteur’s, was added to determine whether any response obtained was biological or chemical.
The Viking LR sought to detect and monitor ongoing metabolism, a very simple and fail-proof indicator of living microorganisms. Several thousand runs were made, both before and after Viking, with terrestrial soils and microbial cultures, both in the laboratory and in extreme natural environments. No false positive or false negative result was ever obtained. This strongly supports the reliability of the LR Mars data, even though their interpretation is debated.