In writing my book,[1] I tried to track down some well-known facts to their sources, only to find that some well-known facts aren’t facts at all. For example, there is a widely bandied-about figure on the number of grains of sand on the earth, credited to a “study” done by “researchers at the University of Hawaii.”
I had to use the WayBack Machine to find the “study,” which turns out to be a rough estimate done by a mathematician named Howard C. McAllister. It was never published in any research journal. Beyond that, McAllister was only trying to estimate the beach sand on the earth; he did not include any deserts.
His old figure for beach sand is 7.5 x 1018, and may be found here. Yeah, click there and check it out. It’s hardly a “study.” It’s an order-of-magnitude estimate. A nice one, but far from definitive, and nothing like a research paper.
I’m going to complete McAllister’s estimate, in hopes that eventually people will find this post for a more comprehensive estimate. In the same spirit as his original, this will be an order-of-magnitude calculation; sticklers for specifics can write their own blogs. My work here is NOT definitive!
The fourteen[2] largest deserts according to geology.com are:
Antactica (no sand)
The Arctic (no sand)
Sahara 3,500,000 square miles
Arabian 1,000,000 mi2
Gobi 500,000
Patagonian (more rocky than sandy)
Great Victoria 250,000 (shallow sand, mostly)
Kalahari 220,000
Great Basin 190,000 (shallow sand, mostly)
Syrian 190,000
Chihauhuan 175,000 (shallow sand, mostly)
Great Sandy 150,000
Kara Kum 135,000
Colorado Plateau 130,000 (shallow sand)
Gibson Desert 120,000
All the other deserts further down the list add up (roughly) to another 700,000 square miles.
That makes a total of 7,260,000 square miles. That’s a lot. Let’s assume (for no good reason and with no evidence whatsoever) that most of the deserts with dunes average ten meters for depth of sand, and that the shallow ones average one meter in depth. The former is probably low and the latter one high, but they are easy numbers, and probably within an order of magnitude.
Converting square miles to square meters then multiplying and summing (see table below) that yields an overall volume of 1.71 x 1014 cubic meters of sand in deserts alone.
Using the same grain volume (1 mm3) used by the UHI mathematicians, we multiply our deserts’ volumes by the number of cubic millimeters in a cubic meter (1,000,000,000) to get:
1.71 x 1023 grains of sand in the world’s deserts.
Whoa. The beaches are totally eclipsed by this number. Adding them together changes nothing.[3] Sand on beaches is comparatively insignificant.
Whoa. The beaches are totally eclipsed by this number. Adding them together changes nothing.[3] Sand on beaches is comparatively insignificant.
The number of galaxies in the visible universe is currently estimated at two trillion (2 x 1012). Each galaxy contains, on average, between 100 billion and 400 billion stars (solar systems), or 1 x 1011 to 4 x 1011.
That gives a range for stars of 2 x 1023 (close to sand!) to 8 x 1023.
It is still true: There are more solar systems in the visible universe than grains of sand on the earth. Just barely. Same order of magnitude, for sure. The weakest part of my reasoning is the depth of sand in the world's deserts. It could easily be ten times what I assumed here, which could put sand in the lead over stars, depending on the average number of stars in each galaxy.
I hope that's helpful.
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[1] Working title: Implications; The Interfaith Promise of Science
[2] Just because.
[3] 1.71 x 1023 + 7.5 x 1018 = 1.710075 x 1023 which rounds to 1.71 x 1023.
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