>> the top meter of soil in your yard probably contains several kilograms of uranium.

No. That is way way off. Grams ... more likely milligrams and even that sounds too much.

According to [1], "the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg." According to [2], the density of topsoil ranges from 1,100 to 2,500 kg/m^3. One acre is about 4,000 m^2, so a conservative estimate is that there is about 1.3 kg of uranium in 1 meter of top soil on a 1 acre lot. (4000 m^3 * 1100 kg/m^3 * 3x10^-7). That's just the low end - taking the midway point for both yields over 40kg (4000 m^3 * 1800 kg/m^3 * 6 mg/kg).

[1] https://en.wikipedia.org/wiki/Uranium_in_the_environment

[2] https://structx.com/Soil_Properties_002.html

  on a 1 acre lot

Not many of us have all of an acre lot for our homes.

According to [1], 2 billion people are subsistence farmers with under 5 hectares. The population adjusted average seems to be around a quarter of a hectare (~0.6 acres) per person (which sounds low to me, as someone who has grown my own food without automation).

10^9 == many of us. Unless your definition of "us" is hacker news readers.

[1] https://en.wikipedia.org/wiki/Subsistence_agriculture

Do the math. Average crustal abundance of U is around 3 ppm.

for a house in my neighbourhood I'd guess ~100 mg

Several milligrams or kilograms?

According to Wikipedia(https://en.wikipedia.org/wiki/Uranium_in_the_environment):

"According to the United Nations Scientific Committee on the Effects of Atomic Radiation the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg."

So let's say 5mg/kg. 200kg of soil per gram. How much area do you need to make 200kg of soil if you're going down 1m? I'd guess not much...

So I think OP is wrong and it's more like 'several grams'.

According to this[1] the weight for 1 cubic meter of dry soil is 1200kg, so 6 grams of uranium per cubic meter.

Looking at average suburban lot sizes, they seem to be about 7200 sqft , which is about 668m^2.

Which gives 668m^3 which gives about 4kg of uranium shockingly.

[1] https://www.reference.com/science/much-cubic-meter-soil-weig...

I thought the numbers from wikipedia looked a little shaky, maybe. I couldn't find those specific numbers in the reference UN PDF.

Google says soil concentration of Uranium is like 3ppm. But, if you do the math, 668 x 1200 x 1000 x (1/1000000) = 802g for every ppm. 3ppm Uranium would be 2.4kg by this number.

Lead is at like 15-40ppm (https://ag.umass.edu/soil-plant-nutrient-testing-laboratory/... ), so between 12 and 32 kg of lead in everyone's back yard?

I first thought that OP estimate was way off, but from your numbers he may be right! If you only need 200 tons of soil for 1kg of Ur, that's not much.

A cubic meter of soil is ~2 tons, maybe more, which means you only need a 10m by 10m square to get 1kg of Ur if you go 1m deep. Wow.

I think getting to enriched uranium is the hard bit.

Also, now your property is a large hole.

I think uranium at that concentration would qualify your lot as a Superfund site. It's a toxic heavy metal and that's a lot. Your numbers might be off by a zero or two.

As others have pointed out here, no, I was not off. It's a bit of a shocker to realize how much U is out there. There's a reason one should test your basement for radon before you buy a house.

But, since people don't mine uranium randomly, one may assume that your back yard doesn't have enough to be price-competitive with modern mines.

Of course. The point is that if a nation wants to make nuclear weapons, keeping them away from uranium is a nonstarter. Uranium is everywhere, if you're willing to pay to extract it (in this case, by piling up the dirt and leaching the uranium using a bicarbonate solution).

Fun fact: if the uranium and thorium in an average crustal rock were totally fissioned (using breeder reactors), the rock would produce about 20x the heat energy of burning the same mass of coal.