by BDanielMayfield » Fri Sep 18, 2020 6:02 pm
Apparently the two words are synonymous. When one looks up Wikipedia's disambiguation page for "biomarker" for this discussion's meaning you get
Biomarker (astrobiology), any substance that provides evidence of past or present life
, but then when you click on the link it takes you to the article for "Biosignature".
I found this part of the biosignature article quite germane to this discussion:
Viability
Determining if a potential biosignature is worth being investigated is a fundamentally complicated process. Scientists must consider any and every possible alternate explanation before concluding that something is a true biosignature. This includes investigating the minute details that make other planets unique and being able to understand when there is a deviation from the expected non-biological processes present on a planet. In the case of a planet with life, it is possible that these differences can be extremely small or not present at all, adding to the difficulties of discovering a biosignature. Years of scientific studies have culminated in three criteria that a potential biosignature must meet in order to be considered viable for further research: Reliability, survivability, and detectability.[5][6][7][8]
Reliability
A biosignature must be able to dominate over all other processes that may produce similar physical, spectral, and chemical features. When investigating a potential biosignature, scientists must be careful to consider all other possible origins of the biosignature in question. There are many forms of life which are known to mimic geochemical reactions. In fact, one of the theories on the origin of life involves molecules figuring out how to catalyze geochemical reactions to exploit the energy being released by them. These are some of the earliest known metabolisms (see methanogenesis).[9][10] In a case such as this, scientists might search for a disequilibrium in the geochemical cycle, which would point to a reaction happening more or less often than it should. A disequilibrium such as this could be interpreted as an indication of life.[10]
Survivability
A biosignature must be able to last for long enough so that a probe, telescope, or human can be able to detect it. A consequence of a biological organism's use of metabolic reactions for energy is the production of metabolic waste. In addition, the structure of an organism can be preserved as a fossil and we know that some fossils on Earth are as old as 3.5 billion years.[11][12] These byproducts can make excellent biosignatures since they provide direct evidence for life. However, in order to be a viable biosignature, a byproduct must subsequently remain intact so that scientists may discover it.
Detectability
For a biosignature to be relevant in the context of scientific investigation, it must be detectable with the technology currently available. This seems to be an obvious statement, however there are many scenarios in which life may be present on a planet, yet remain undetectable because of human-caused limitations.
False positives
Every possible biosignature is associated with its own set of unique false positive mechanisms, or non-biological processes that can mimic the detectable feature of a biosignature. An important example of this is using oxygen as a biosignature. On Earth, the majority of life is centered around oxygen. It is a byproduct of photosynthesis and it is subsequently used by other forms of life to breathe. Oxygen is also readily detectable in spectra, with multiple bands across a relatively wide wavelength range, therefore it makes a very good biosignature. However, finding oxygen alone in a planet's atmosphere is not enough to confirm a biosignature because of the false positive mechanisms associated with it. One possibility is that oxygen can build up abiotically via photolysis if there is a low inventory of non-condensible gasses or if it loses a lot of water.[13][14] Finding and distinguishing a biosignature from its potential false positive mechanisms is one of the most complicated parts of testing for viability because it relies on human ingenuity to break an abiotic-biological degeneracy, if nature allows.
False negatives
Opposite to false positives, false negative biosignatures arise in a scenario where life may be present on another planet, but there are some processes on that planet that make potential biosignatures undetectable.[15] This is an ongoing problem and area of research in the preparation for future telescopes that will be capable of observing exoplanetary atmospheres.
Human limitations
There are many ways in which humans may limit the viability of a potential biosignature. The resolution of a telescope becomes important when vetting certain false positive mechanisms, and many current telescopes do not have the capabilities to observe at the resolution needed to investigate some of these. In addition, probes and telescopes are worked on by huge collaborations of scientists with varying interests. As a result, new probes and telescopes carry a variety of instruments that are compromises to everyone's unique inputs. In order for a different type of scientist to be able to detect something not related to biosignatures, a sacrifice may have to be made in the capability of an instrument to search for biosignatures.[16]
Therefore, a
potential biomarker or biosignature can be either true or false. Like Schrödinger's cat, this 'biomarker' in the Venus atmosphere is merely a potential one until we open the box to see if the cause is biological or not.
Apparently the two words are synonymous. When one looks up Wikipedia's disambiguation page for "biomarker" for this discussion's meaning you get
[quote]Biomarker (astrobiology), any substance that provides evidence of past or present life[/quote], but then when you click on the link it takes you to the article for "Biosignature".
I found this part of the biosignature article quite germane to this discussion:
[quote][b]Viability[/b]
Determining if a potential biosignature is worth being investigated is a fundamentally complicated process. [color=#FF0000]Scientists must consider any and every possible alternate explanation before concluding that something is a true biosignature.[/color] This includes investigating the minute details that make other planets unique and being able to understand when there is a deviation from the expected non-biological processes present on a planet. In the case of a planet with life, it is possible that these differences can be extremely small or not present at all, adding to the difficulties of discovering a biosignature. Years of scientific studies have culminated in three criteria that a potential biosignature must meet in order to be considered viable for further research: Reliability, survivability, and detectability.[5][6][7][8]
[b]Reliability[/b]
A biosignature must be able to dominate over all other processes that may produce similar physical, spectral, and chemical features. When investigating a potential biosignature, scientists must be careful to consider all other possible origins of the biosignature in question. There are many forms of life which are known to mimic geochemical reactions. In fact, one of the theories on the origin of life involves molecules figuring out how to catalyze geochemical reactions to exploit the energy being released by them. These are some of the earliest known metabolisms (see methanogenesis).[9][10] In a case such as this, scientists might search for a disequilibrium in the geochemical cycle, which would point to a reaction happening more or less often than it should. A disequilibrium such as this could be interpreted as an indication of life.[10]
[b]Survivability[/b]
A biosignature must be able to last for long enough so that a probe, telescope, or human can be able to detect it. A consequence of a biological organism's use of metabolic reactions for energy is the production of metabolic waste. In addition, the structure of an organism can be preserved as a fossil and we know that some fossils on Earth are as old as 3.5 billion years.[11][12] These byproducts can make excellent biosignatures since they provide direct evidence for life. However, in order to be a viable biosignature, a byproduct must subsequently remain intact so that scientists may discover it.
[b]Detectability[/b]
For a biosignature to be relevant in the context of scientific investigation, it must be detectable with the technology currently available. This seems to be an obvious statement, however there are many scenarios in which life may be present on a planet, yet remain undetectable because of human-caused limitations.
[b]False positives[/b]
Every possible biosignature is associated with its own set of unique false positive mechanisms, or non-biological processes that can mimic the detectable feature of a biosignature. An important example of this is using oxygen as a biosignature. On Earth, the majority of life is centered around oxygen. It is a byproduct of photosynthesis and it is subsequently used by other forms of life to breathe. Oxygen is also readily detectable in spectra, with multiple bands across a relatively wide wavelength range, therefore it makes a very good biosignature. However, finding oxygen alone in a planet's atmosphere is not enough to confirm a biosignature because of the false positive mechanisms associated with it. One possibility is that oxygen can build up abiotically via photolysis if there is a low inventory of non-condensible gasses or if it loses a lot of water.[13][14] Finding and distinguishing a biosignature from its potential false positive mechanisms is one of the most complicated parts of testing for viability because it relies on human ingenuity to break an abiotic-biological degeneracy, if nature allows.
[b]False negatives[/b]
Opposite to false positives, false negative biosignatures arise in a scenario where life may be present on another planet, but there are some processes on that planet that make potential biosignatures undetectable.[15] This is an ongoing problem and area of research in the preparation for future telescopes that will be capable of observing exoplanetary atmospheres.
[b]Human limitations[/b]
There are many ways in which humans may limit the viability of a potential biosignature. The resolution of a telescope becomes important when vetting certain false positive mechanisms, and many current telescopes do not have the capabilities to observe at the resolution needed to investigate some of these. In addition, probes and telescopes are worked on by huge collaborations of scientists with varying interests. As a result, new probes and telescopes carry a variety of instruments that are compromises to everyone's unique inputs. In order for a different type of scientist to be able to detect something not related to biosignatures, a sacrifice may have to be made in the capability of an instrument to search for biosignatures.[16][/quote]
Therefore, a [u]potential[/u] biomarker or biosignature can be either true or false. Like Schrödinger's cat, this 'biomarker' in the Venus atmosphere is merely a potential one until we open the box to see if the cause is biological or not.