# Mt Toba **URL:** \ **Category:** Factual Questions\ **Created:** [February 28, 2000, 8:28pm UTC](https://boards.straightdope.com/t/mt-toba/7840 "2000-02-28T20:28:00Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Jois](https://avatars.discourse-cdn.com/v4/letter/j/ea666f/32.png) [@Jois](https://boards.straightdope.com/u/Jois)\ **Post date:** [February 28, 2000, 8:28pm UTC](https://boards.straightdope.com/t/mt-toba/7840/1 "2000-02-28T20:28:00Z")
This was supposed to be a BIG event in earth’s history - 400 times bigger than the volcano at Mt St Helens – but the event doesn’t get a lot of mention in the human evolution circles… Or am I missing it? It should have made that critical bottle neck needed for evolutionary change and wiping out those old Homo genus to make way for modern man. So is it fact or fiction? (Visualize Far Side cartoon and two Neandethals laughing all the way to the cave.) * * * Are you driving with your eyes open or are you using The Force? - A. Foley ---
**Author:** ![Fillet](https://avatars.discourse-cdn.com/v4/letter/f/2acd7d/32.png) [@Fillet](https://boards.straightdope.com/u/Fillet)\ **Post date:** [February 28, 2000, 9:34pm UTC](https://boards.straightdope.com/t/mt-toba/7840/2 "2000-02-28T21:34:00Z")
This is more like stretching available data veeerrrryyyy ffffaaaarrrr… The Toba eruption was indeed pretty damn big, ad it left a lot of people wondering about possible aftereffects. To go on and say that it led to an evolutionary bottleneck critical for human evolution requires to things to be true: 1. Large volcanic eruptions have the ability to change climate dramatically for years, leading to the dying off of plant life and the starvation of all creatures higher up the food chain (a la the “nuclear winter” scenario that was a popular topic during the Reagan administration). 2. Rates of evolutionary change can be accurately determined, and thus the timing of major evolutionary developments can be calculated. I don’t think anyone would dispute the fact that massive volcanic eruptions have the ability to perturb global weather patterns. How much cooling is a matter of debate. A paper from 1990 sums things up nicely; the general view hasn’t changed much over the past decade: > [@](#): > > EVIDENCE OF VOLCANIC LOADING OF THE ATMOSPHERE AND CLIMATE RESPONSE: H. Sigurdsson, Global and Planetary Change v. 89(3), p. 277-289, 1990. > > Abstract: Global climatic effects brought about by volcanism are most likely to be related to the impact of volcanic gases and their derivative aerosols on the atmosphere, rather than the effects of volcanic ash. Evidence from both historic eruptions and polar ice cores indicates that volcanic sulfur gases are the dominant aerosol-forming > component, resulting in production of a sulfuric acid-rich stratospheric aerosol that can have profound effects on the Earth’s radiation budget over periods of a few > years. Due to highly variable sulfur content of different magma types, the climatic effects do not relate simply to total erupted mass. Data on several recent eruptions indicate a close relationship between volcanic sulfur yield to the atmosphere and hemispheric surface temperature decrease following the eruptions, with up to 1-degrees-C surface temperature decrease indicated following a major volcanic event such as the 1815 Tambora eruption. While the erupted mass of HCl and HF is equal to or greater than that of sulfur gases in a number of volcanic events, the halogens do not form known aerosols nor are they abundant in ice core acidity layers. > Current opinion favors the early removal of halogens from eruption columns by rain flushing and adsorption onto tephra particles, but the fate of halogens in the atmosphere following very large explosive eruptions remains unstudied. CO2 flux to the atmosphere from volcanic eruptions is volumetrically one of the most important of the gas species, but owing to the huge size of the atmospheric reservoir of this gas, the volcanic contribution is likely to have negligible effects, even for event on the scale of the Deccan Traps. For the Toba eruption, Sigurdsson suggests that there was a 2-4 degree C drop in average global temperatures, although there’s apparently a problem in trying to separate the effects of the eruption from the glacial conditions that already existed at that time. In my view, if the eruption’s effects can hardly be separated from longer-term climae variability, the “doomsday” scenario that some geologists present (e.g., Mike Rampino of NYU) does not seem very likely. (Side note: Prof. Rampino’s research focus is on mass extinctions and catastrophic events, so he’s not exactly viewing the Toba event with an unbiased eye.) As for rates of evolution - molecular systematics studies are fascinating with respect to the evolutionary relationships that they can reveal. However, if you want to know when two species diverged _in time_, and not just on a cladogram, you have to start making assumptions about the average rate of mutation for the genetic markers that you’re using. One can attempt to make reasonable estimates, but it is a huge leap to assume that mutation rates are reliably static over the interval of interest to you. Another thing… Prof. Rampino and his anthropologist colleague, Stanley Ambrose, have calculated a population crash of Homo down to 10,000 in the aftermath of Toba. I haven’t read their paper, but presumably they are estimating the size of the population based upon maternal lineages (through mitochondrial DNA). However, it is not clear to me whether either scientist has considered all those Homo lineages that could have survived Toba but died out sometime later from other causes. In sum, the silence you’ve noticed IMHO relates to the huge uncertainties involved. ---
**Author:** ![tanstaafl](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tanstaafl](https://boards.straightdope.com/u/tanstaafl)\ **Post date:** [February 29, 2000, 3:58am UTC](https://boards.straightdope.com/t/mt-toba/7840/3 "2000-02-29T03:58:00Z")
At least some scientists think so. See the article _Ancient ‘volcanic winter’ tied to rapid genetic divergence in humans_ at [http://www.admin.uiuc.edu/NB/98.09/volcanictip.html](http://www.admin.uiuc.edu/NB/98.09/volcanictip.html) * * * My board got hacked and all I got was this lousy sig file… ---
**Author:** ![Jois](https://avatars.discourse-cdn.com/v4/letter/j/ea666f/32.png) [@Jois](https://boards.straightdope.com/u/Jois)\ **Post date:** [February 29, 2000, 4:44am UTC](https://boards.straightdope.com/t/mt-toba/7840/4 "2000-02-29T04:44:00Z")
Thank you! Tanstaafl’s cite is exactly what I must have seen quoted in print someplace and Fillet says why it might not have been as fatal as advertised! At 71,000 it would still be too early for the bottle that would create the differences we see as race. Jois * * * Are you driving with your eyes open or are you using The Force? - A. Foley