Parent comment is making a joke about “year” as a unit measuring how many times you go around the sun. Less time has passed for the core per relativity, but is it not the same number of years?

The more official definition of years defines it in terms of days, which break down further to SI’s rigorously defined second as the base unit of time. But it’s still weird to think about.

Unless the second is defined on a Hubble flow co-moving observer, it's ill-defined enough to be ambiguous by at least 2 years out of 4 billion.

Yes, you wouldn't be able to measure it accurately, but it's nonetheless a static amount of time unrelated to the Earth's orbital period.

I'm not an astrophysicist, but I'd guess the Earth's orbital period isn't quite the same as when the planet first formed either. So using today's defined measurement of "years", the planet's age and the number of times it's been around the sun might not match up at the surface either. The impact that formed the moon must have changed our velocity a bit, right? And the sun has been losing mass (into energy via fusion) since it first formed.

That explains how it can be ...does the conversion... 75 megaseconds younger, but the whole of the earth modulo ejected material like spacecraft should be the same number of _years_ old.