Radon
A good ²³⁸Umbrella policy should cover it.
A good ²³⁸Umbrella policy should cover it.
This comic was the first in a series (of at least two comics) about absurd results of home inspections. The second, 3059: Water Damage came out less than two months after this one.
In this comic, Ponytail approaches Cueball about the concentration of radon in his basement. This refers to a common phenomenon where the levels of radon gases can build up in enclosed spaces over time; they form out of traces of uranium embedded in the surrounding bedrock/soils of most basements, and in the silicate minerals used in the concrete of the foundation. This uranium (over time, and in most cases via the midpoint of thorium) releases radon as a gas whilst experiencing alpha decay, although the time in which this occurs is noticeably long. Uranium-238 (238U or U-238), the isotope mentioned in the title text, has a half-life of 4.5 billion years, which is about the age of the Earth. Over the whole Earth, roughly 2.8 ppm of the planet is made of uranium; this is about 0.00028% of the planet, which weighs about 5.9722×1024 kilograms. Even so, if uranium existed in the Earth's crust alone - about 1% of the Earth's total mass itself - this would imply that there is 1.67×1019 kilograms of uranium across the entire planet. Thus, radon gas is a relatively commonplace phenomenon, and radon mitigation techniques are frequently employed to keep the air safe and breathable. Basements, in particular, are known to accumulate radon gas if they are kept sealed over a long enough time, that is, with the windows and doors closed. Small cracks in the house's foundation may allow some radon gas to seep inside, which can be cleared if the basement is properly ventilated. Radon is denser than air, but this isn't why it accumulates in basements; it mixes completely with air, and does not "settle out" because of its atomic weight or density. Rather, its concentrations are higher in the basement than elsewhere in a building because the basement is adjacent to rock and the house foundation where it is generated, and because of the relatively poor air circulation usual in basements. Undisturbed, the concentration of radon reaches a steady state in a given area, between accumulation from being generated, and removal by air circulation and by radioactive decay.
In the comic Cueball is getting his house inspected; this is common in preparation for selling the home. Inspector Ponytail finds an excessive level of radon in the basement. Often when problems are found in a home, it's due to the age of the building, since technology has improved over time and building codes have added requirements in parallel.
But rather than inquire about the age of the home, Ponytail asks about the age of the planet on which it was built. The answer would be the same for all houses on Earth. Apparently she's an interstellar inspector, testing properties on many different planets in different star systems with different levels of radon - since most planets in a given system form within a few million years of each other and would have similar levels of radon. Earth's age of 4.5 billion years is about the same as the half-life of U-238, so radon levels are high because much of the original uranium is still in the process of decaying. She recommends waiting 100 billion years - much longer than the expected lifetime of Cueball,[citation needed] the building, and the Sun as we know it - enough to cause U-238 to decay to a trivial amount, not factoring in other daughter nuclides due to their comparatively shorter half-life.
The Sun is an example of a G-type main sequence star, also known as a yellow dwarf, which the inspector notes is a short-lived star. In the next 1 billion years the Sun will become more luminous and end life on Earth, and in 4 to 7 billion years the Sun's outer layers will expand, turning it into a red giant that will likely engulf the Earth. If we'd 'built' around an M-type red dwarf we could have comfortably waited for the uranium to fully decay, though being in the habitable zone of a red dwarf has its own difficulties.
The title text for this comic mentions an umbrella policy, a type of insurance policy that covers damages beyond those covered by another, primary policy. It makes a joke with the isotope representation of uranium-238 being 238U, and is something that Cueball might need to consult with after handling the issue of radon gas in his home; most states in the United States, for instance, require property disclosure forms to be filled out if radon levels surpass a certain threshold. This text may also be an oblique reference to the concept of a nuclear umbrella, an altogether different kind of "insurance".