Ask “how do they know that?” about any big claim. It’s the most useful question in science class and outside it.

Every claim has a method behind it, and the method is where the real content sits. Asking how somebody knows reveals whether there was a measurement, a model, a guess or a single story, and that changes how much weight the claim can carry. It is a polite question rather than an aggressive one, and it works on textbooks as well as strangers online.

Try it on one striking claim a day for a week, including the ones you like. Look for how the number was arrived at. Some claims turn out to have nothing underneath them at all.