Category
How we know what we know. Explainers that show the evidence and the method, not just the conclusion.
It is not distance from the Sun — in fact Earth is closest to the Sun in early January, during northern winter. The real mechanism is a 23.4° tilt doing two things at once, and one of them is easy to overlook.
4.54 billion years, give or take 50 million. The strange part is that the number comes from meteorites rather than Earth rocks — and the reason why is the most interesting thing in the whole story.
A vaccine is a training exercise: it shows your immune system a recognisable fragment of a pathogen without the pathogen. Here is the actual biology — antigens, memory cells, why boosters exist, and where the herd-immunity threshold number comes from.