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When we talk about mass extinctions, we're mostly talking about marine life. Mass extinctions are dominated by a reduction in marine biodiversity, simply becau

by jofer 12y ago

When we talk about mass extinctions, we're mostly talking about marine life. Mass extinctions are dominated by a reduction in marine biodiversity, simply because that's what dominates the fossil record. (Beyond that, there's no land life for the first of the 5 major extinction events, and little data for land life for the next two.) However, marine organisms would be sheltered from gamma radiation. From a geological viewpoint, this seems very unconvincing as a significant cause of any the major mass extinction events. It's interesting for extraterrestrial life and future society in general, though.

fiatmoney 12y ago
Many deep-water marine ecosystems are dependent on their neighbors in near-surface environments.
- jofer 12y ago
  Sure! They're tied to the shallow marine ecosystem. Most marine productivity is within the photoic zone, as well. Marine ecosystems are typically not tightly tied to land life, though. (Sediment input, etc, is a different story, but while it's biologically mediated, it's not controlled by biologic factors.) However, even a fraction of a meter of water will form a very effective barrier to gamma radiation (One meter reduces it to ~2e-17 times it's original intensity). Even if it were to kill off everything in the upper few tens of centimeters of water, it wouldn't decimate marine productivity. Most of the productivity in the oceans is tied to the ecosystem in the photoic zone, but not to the upper few centimeters of the water column. Edit: I just realized they're mostly referring to the effect of increased UVB radiation _after_ the gamma ray burst removes the ozone layer, rather than the effect of the gamma ray burst itself. Because UV radiation is much longer wavelength, it would have an effect on the upper few meters of the water column, rather than the upper few centimeters, which could be significant. I'm still unconvinced that it's a "good" explanation for mass extinctions, given that we have several others (e.g. long-term sea level fluctuations), but it makes more sense than I thought at first.
dnautics 12y ago
Half of the earth's surface would be fried instantly by a GRB. The other half would be protected, forget a few meters of water, by the bulk of the planet. The kicker, though is the sudden conversion of a large part of the atmosphere into nitric acid. (O2 + gamma -> NO, NO + H2O + O2 -> HNO3 - I'm not gonna balance that). That will cause serious imbalances in ocean chemistry and also be uncomfortable for terrestrial life on the other half of the planet as it diffuses over.
dghughes 12y ago
>However, marine organisms would be sheltered from gamma radiation. Phytoplankton may not since it's on the surface (for sunlight access) and at 50% of atmospheric oxygen comes from ocean algae, at least as much as plants.
- jofer 12y ago
  It would be sheltered from gamma radiation. Even a few tens of centimeters of water is enough. (Phytoplankton is dispersed throughout the upper 50 meters or so, though it's concentrated closer to the surface.) UVB from sunlight after the gamma ray burst strips away the issuing layer is what people are referring to. Because it's longer wavelength, it could still have an effect.

by jofer 12y ago

fiatmoney 12y ago

Many deep-water marine ecosystems are dependent on their neighbors in near-surface environments.

jofer 12y ago
Sure! They're tied to the shallow marine ecosystem. Most marine productivity is within the photoic zone, as well. Marine ecosystems are typically not tightly tied to land life, though. (Sediment input, etc, is a different story, but while it's biologically mediated, it's not controlled by biologic factors.) However, even a fraction of a meter of water will form a very effective barrier to gamma radiation (One meter reduces it to ~2e-17 times it's original intensity). Even if it were to kill off everything in the upper few tens of centimeters of water, it wouldn't decimate marine productivity. Most of the productivity in the oceans is tied to the ecosystem in the photoic zone, but not to the upper few centimeters of the water column. Edit: I just realized they're mostly referring to the effect of increased UVB radiation _after_ the gamma ray burst removes the ozone layer, rather than the effect of the gamma ray burst itself. Because UV radiation is much longer wavelength, it would have an effect on the upper few meters of the water column, rather than the upper few centimeters, which could be significant. I'm still unconvinced that it's a "good" explanation for mass extinctions, given that we have several others (e.g. long-term sea level fluctuations), but it makes more sense than I thought at first.

dnautics 12y ago

Half of the earth's surface would be fried instantly by a GRB. The other half would be protected, forget a few meters of water, by the bulk of the planet. The kicker, though is the sudden conversion of a large part of the atmosphere into nitric acid. (O2 + gamma -> NO, NO + H2O + O2 -> HNO3 - I'm not gonna balance that). That will cause serious imbalances in ocean chemistry and also be uncomfortable for terrestrial life on the other half of the planet as it diffuses over.

dghughes 12y ago

>However, marine organisms would be sheltered from gamma radiation. Phytoplankton may not since it's on the surface (for sunlight access) and at 50% of atmospheric oxygen comes from ocean algae, at least as much as plants.

jofer 12y ago
It would be sheltered from gamma radiation. Even a few tens of centimeters of water is enough. (Phytoplankton is dispersed throughout the upper 50 meters or so, though it's concentrated closer to the surface.) UVB from sunlight after the gamma ray burst strips away the issuing layer is what people are referring to. Because it's longer wavelength, it could still have an effect.