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