# Age of earth relative to other planets

Relative to the average age of other known planets, is the earth young, old or in the middle? Does it make a difference if you compare the earth against nearby planets (say < 500 LY), or other planets in our galaxy, or other galaxies?

• We don't (yet) have the technology to observe planets in other galaxies. We are just starting to be able to resolve individual stars in other galaxies from the Local Group. Jan 8 '20 at 7:47

Another way of estimating whether Earth is young or old is to compare to star formation rate estimates across the history of the universe. This is of course also presently uncertain and may be different in different galaxies (elliptic galaxies have low star formation, so their planets would tend to be older than the ones in spiral and irregular galaxies). Overall, it appears to have peaked 3.5 Gyr after the big bang and has declined since. That would perhaps make the average planet that ever formed much older ($$\approx 10$$ Gyr old) than Earth.