Role of radio isotopes in dating the past
When we age date a planet, we are actually just dating the age of the surface, not the whole planet.
We can get absolute ages only if we have rocks from that surface.
For others, all we are doing is getting a relative age, using things like the formation of craters and other features on a surface.
By studying other planets, we are learning more about our own planet.
Carbon-14 has a half life of 5730 years, meaning that 5730 years after an organism dies, half of its carbon-14 atoms have decayed to nitrogen atoms.