Why was the positive result from the Viking Labeled Release (LR) experiment generally dismissed by the scientific community?
Other biological experiments failed to find necessary organic molecules
The Viking landers conducted multiple experiments to test Martian soil for signs of life in 1976. The Labeled Release (LR) experiment was particularly tantalizing because it showed a rapid release of gas when nutrient-laced broth was added, suggesting some form of biological process. However, this result was contradicted by the failure of the other biological experiments on Viking, specifically those designed to detect organic molecules, which are considered the essential chemical building blocks of life as understood on Earth. This contradiction led the majority of the scientific community to conclude that the LR result was likely an artifact caused by non-biological, or abiotic, chemistry present in the Martian soil, such as highly reactive oxidants, rather than actual living microbes.
