The annual effective* radiation dose from the soil, rocks, etc. is ~21 millirem (mrem). This is about 3% of the 620 mrem total annual effective dose that the average person receives from all natural and man-made sources (which are mostly medical). It is also less than 1/5 the dose from a medical CT scan (see Table 1 here but note that the table is in milliSieverts (mSv) which converts to mrem as 1 mSv = 100 mrem; the table therefore ranges from 2 mrem to 1600 mrem.)

Overall, the radiation exposure from natural background is considered a low dose. While there is considerable uncertainty about the effects of prolonged low dose exposures, the increase in likelihood of cancer from radiation is low compared to the natural risk of cancer . For medical procedures, the increased risk might be so low that it can't even be reliably measured, but medical exams have been directly linked to increased life expectancy and lower cancer death rates (not in source, but presumably from earlier detection which allows treatment before the cancer has progressed to a fatal level).

Another natural background radiation source related to soil is radon gas (often listed as radon and thoron, but thoron is just an isotope of radon). The average annual effective radiation dose from radon and other radioisotopes is 257 mrem (of which bananas contribute ~0.01 mrem due to potassium-40), about 10 times higher than the dose from soil and about the same as some medical scans. Radon is naturally produced through the nuclear decay of higher number elements like uranium-238 and thorium-234. Uranium and thorium are naturally present in small amounts in some rocks, and radon that is released as they break down can accumulate in homes or other places with people.

Radon exposure has been linked to ~20,000 additional cases of lung cancer per year, with about 90% of those being in smokers who are already predisposed toward lung cancer. For comparison, smoking alone causes 160,000 cancer deaths each year, 8 times as many as radon. The current EPA guidelines for radon are to test your home and add a mitigation method if it measures 4 picoCuries per liter or more (picoCuries, abbreviated pCi, is a unit of radioactive decay per time). The appropriate mitigation method varies depending on the house and the measurement, but can be as simple as opening a window and adding a fan.

* The effective dose is adjusted for the magnitude of the dose and the portion of the body to which it is delivered. This is because a small dose to the entire body is more harmful than a large dose to a small portion of the body.

Not sure precisely what you are asking…. blackbody radiation is everywhere… so the Sun heats the soil and the soil radiates in the IR part of the spectrum; but that is not particularly harmful. Are you thinking about the flux of high energy photons a associated with radioactive decay from uranium, or potassium, or thorium, in the atoms locked up in clay minerals? If so, this radiation is very, very low flux…, unless the soil perhaps around an old uranium mine or some very special geological environment, this radiation is not too dangerous. There are cases where radioactivity in some cinder blocks used to build an underground structure like a basement, could potentially be something to test for, by testing for radon, a decay product. But again this is rather uncommon overall.

Great to hear this question Lauro! Many sources give us radiation dose. Those can be the sun, food we eat and from the soil. One way we measure dose is in milli-rem or mrem. To answer your great question, we each receive ~20 mrem from the soil on Earth a year.

The good news is due to the minuscule amount, there's nothing to worry about! A whopping 500 times that dose is safe.

Fun fact: Did you know a banana contains ~0.01 mrem of dose? Enjoy your bananas because you'd need to eat over 500,000 bananas a year to harm anything!

This depends greatly on where you live. Rocks containing uranium produce radon gas, as the uranium in the rocks decays. Radon can seep into the lower levels of houses, and can be very dangerous if chronically inhaled. According to the EPA, the largest single fraction of radioactivity that human beings as a whole are exposed to is either radon or from medical procedures.

However, since it varies so much depending on where you live, you may or may not be affected.

On average, Americans receive a radiation dose of about 0.62 rem (620 milli-rem) each year. Half of this dose comes from natural background radiation. Most of this background exposure comes from radon in the air, with smaller amounts from cosmic rays and the Earth itself.