Global Bubbling

Scientific American magazine offers some of its articles online for free. Free material from the October issue includes Impact From the Deep, which gives evidence that some mass-extinctions in Earth history were not caused by asteroid impacts but by massive upwellings of hydrogen sulfide (H2S) gas from the oceans. Here’s the scenario:

  1. High levels of volcanic activity leading to high levels of atmospheric CO2 and methane.
  2. Increase in global atmospheric temperatures due to a stronger greenhouse effect.
  3. Increase in oceanic temperatures.
  4. Decrease in oceanic oxygen content (warm water holds less dissolved gas).
  5. Lower oceanic oxygen content allows H2S-rich water from depth to rise to the surface.
  6. Poisonous H2S causes mass-extinctions in the oceans.
  7. H2S diffuses into the atmosphere, killing many land plants and animals.

The level of atmospheric CO2 that accompanied this bubbling of oceanic H2S was around 1000 ppm. The current CO2 concentration is 385 ppm, with an increase of 2-3 ppm per year. At this rate, CO2 could be at 900 ppm by the end of the century. The warning: Higher levels of greenhouse gases in the atmosphere could lead not only to global climate change, but also to global H2S asphixiation.

Here is my initial response:

  • The article was written by Peter Ward, one of the authors of the respected book Rare Earth. That gives it credibility.
  • The data seems sound. We can get a good understanding of past global CO2 levels, H2S levels, and rates of extinction through carbon isotope studies and paleontology.
  • From the following graph, There were also long periods of elevated CO2 levels which did not lead to mass-extinctions. This may be the greatest weakness of the hypothesis.


Graphic from Scientific American

  • Because of this, the investigators may have a good hypothesis, but it still needs work.
  • Of course, many will dismiss this as the just the latest unlikely disaster scenario from wild tree-hugging environmentalist wackos. But if it is to be dismissed, it should be on scientific merits, not because of a knee-jerk reaction.

Grace and Peace

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