Wednesday, December 4, 2013

Dino Water: Response to XKCD's "What If"

Randall Munroe's concluding image.  Image source.
XKCD is a popular webcomic by Randall Munroe that often uses science, math, and engineering in its jokes.  Aside from the main comics published every Monday, Wednesday, and Friday, XKCD presents a special "What If" comic on Tuesdays that explores hypothetical situations and questions submitted by readers.

Yesterday, Munroe calculated how much of the earth's water has been in a soft drink at some point in history (0.0000005%, if you were wondering).  In typical XKCD fashion, Munroe takes the answer a step further and calculates that almost all water on earth has been drunk by at least one dinosaur.  This conclusion is, of course, based on numerous assumptions, including the number of dinosaurs alive at a given time, the average dinosaur weight, and the similarity of dinosaur metabolism to that of mammals.  I use the word "assumption" lightly here, as these figures were calculated from best-estimates rather than random guesses.  Additionally, Munroe assumed that dinosaurs existed for hundreds of millions of years through the Mesozoic Era, which coincides with the evolutionary view of life, but not with a creationist model.  I say this not to criticize Munroe, but to wonder how different the conclusion would be based on a more biblical model.

As an estimate of the biomass (total weight) of dinosaurs at any given time, Munroe refers to this paper by Jerzy Trammer, which gives varying figures throughout the Mesozoic, ranging from 255 billion kg to 6.69 trillion kg, based on mammal population density and geographic ranges applied to all land.  In the creation model, the various groupings of dinosaurs represented by these figures were not separated by time, but by geography, so the densities and ranges can't necessarily be applied to the whole earth.  Instead, we can estimate that the different dinosaurian ecosystems were somewhat evenly abundant, so we may take an average of Trammer's figures to get about 2.8 trillion kg of dinosaurs before the Flood.  However, this figure also assumes that mammals and birds did not compose a significant portion of the biomass, which is not the case in the creationist model, so it may be prudent to trim it down some.  I have no numbers to refer to, so I will simply divide it in half, giving us 1.4 trillion kg of dinosaurs (this won't have a large effect on the order of magnitude of the final number).

According to a document from the Ministry of Environment of British Columbia, mammals drink approximately 8.91% of their body mass per day.  If we assume, as Munroe did, that dinosaurs drank at similar rates, then we can estimate that the total dinosaur population drank about 125 billion liters of water per day before the Flood.  Given 1656 years between Creation and the Flood, this implies that, in total, dinosaurs drank on the order of 1016 to 1017 liters of water.  I will discount any post-Flood dinosaur drinking as relatively insignificant to these values.

What effect do these values have on the conclusion?  According to Munroe and the USGS, there are about 1021 liters of water currently on the earth, so by the creation model, only .01 to .001% of it was likely drunk by dinosaurs at some point.  If all of the water was very well mixed by the Flood and other events, then this still means that at least some of the water in your cup was drunk by a dinosaur at some point, but not as much as Munroe's calculations suggest.

No comments:

Post a Comment