How did you establish that the carbon dioxide or other components in gas bubbles of ice cores was unaffected by the presence of microorganisms at the time the ice formed, or in some intervening time by psychrophiles. I know blood gas specimens degrade very rapidly on their way to the lab. How do we know old gas pockets are truly unchanged over time despite what might have been present in their containers?
The idea is that the gas diffusion rate for old bubbles is extremely low under those conditions, so they're a reliable scribe of the local atmosphere at the time (including contaminants). I don't think the CO2 abundance is completely unaffected, and in fact some interesting paleo-biology has been done on the bacterial species found, but biological respiration (a) has a net positive impact on CO2 abundance (so the observed raw concentration is probably an *overestimate*), (b) also generates additional molecules not present in uncontaminated samples, so it can be corrected for, and (c) so many samples have been collected at a continuum of depths and locations around the globe that the overall effect on any particular over-contaminated sample is smoothed out.
Very kind! A good fraction of my job is teaching science to gen-ed (non-major) students, and I'm a bit frustrated as well that the crucial chain of reasoning isn't often spelled out. At this level, I'm not even as interested in talking about solutions or policy until there's at least some broad agreement on what is actually happening.
just gonna put a link to this on page 1 of my dissertation and call it good
How did you establish that the carbon dioxide or other components in gas bubbles of ice cores was unaffected by the presence of microorganisms at the time the ice formed, or in some intervening time by psychrophiles. I know blood gas specimens degrade very rapidly on their way to the lab. How do we know old gas pockets are truly unchanged over time despite what might have been present in their containers?
The idea is that the gas diffusion rate for old bubbles is extremely low under those conditions, so they're a reliable scribe of the local atmosphere at the time (including contaminants). I don't think the CO2 abundance is completely unaffected, and in fact some interesting paleo-biology has been done on the bacterial species found, but biological respiration (a) has a net positive impact on CO2 abundance (so the observed raw concentration is probably an *overestimate*), (b) also generates additional molecules not present in uncontaminated samples, so it can be corrected for, and (c) so many samples have been collected at a continuum of depths and locations around the globe that the overall effect on any particular over-contaminated sample is smoothed out.
I love this. I work with the UN on climate change and I’d love to see them explain things so clearly ...
Very kind! A good fraction of my job is teaching science to gen-ed (non-major) students, and I'm a bit frustrated as well that the crucial chain of reasoning isn't often spelled out. At this level, I'm not even as interested in talking about solutions or policy until there's at least some broad agreement on what is actually happening.