Talmudic Question #4

What if all the bacteria and archaea on Earth decided to go on strike and stop their metabolism all at once? Which of the global cycles of matter would be affected first? How long would it take for life as we know it to come to a stop?

Comments

[Stanley Maloy]

Both of the scenarios proposed by David Lipson make perfect sense, but they only focus on bacteria external to plants and animals (as prompted in the question). However, you could also ask what would be the impact from the demise of the normal microbial biota. Would there be a rapid effect on plant and animal life or a slow effect?

[david lipson]

Here are two scenarios, in order of decreasing reasonability:

(1) Our demise is driven by the N cycle: Most available N pools in soils would be used up in about 1 week (e.g. typical soil inorganic N concentration: 0.1-1 g N/m2, typical plant requirement, 5-50 g N/m2/year, therefore, ~1/50th year before growth halts.) (Probably about the same in oceans, but much oceanic photosynthesis is microbial anyway.)

So, no more growth of photosynthetic organisms after about 1 week. N-limited plants could weakly photosynthesize for a short while, storing starch somewhere, but without a growth sink, it would soon halt. Also, with no more N for protein turnover, even evergreen leaves would be dead in a year or less.

With no more photosynthesis, if humans had an everlasting supply of canned pork and beans, CO2 would slowly build up due to animal respiration and fossil fuel use and lead to greenhouse death of the planet. However, at 2 Gt C/year respiration and 7 Gt C/year from fossil fuels, this would take hundreds of years.

Scenario 2: Plants kept alive by absurdly huge, planetary fertilizer inputs:

Photosynthesis continues, but microbial respiration stops. This leads to about 60 Gt C/year being sucked out of the atmosphere and left in non-decomposing biomass. This would deplete the atmospheric CO2 pool in about 12.5 years, leading to dead plants and a snowball earth. One complication of this scenario is that the ocean could slow this process by releasing dissolved CO2 into the atmosphere. Also, if humans increased fossil fuel use by 10 fold (which probably still isn't enough to produce enough fertilizer for this scenario), we could balance out the photosynthesis with industrial CO2

David Lipson