The hydrogen atoms are mostly
as old as the universe (13 or 14 billion years).
A few hydrogen atoms resulted from proton emission
from unstable, radioactive atoms.
I am referring to the nuclei of atoms
because all atoms exchange electrons with each other,
with very little encouragement,
like chemical reactions,
or even just light shining on them.
Almost all of the heavier atoms formed
during the past 14 billion years,
as they fused hydrogen into helium
and then fused helium into even heavier atoms,
and then exploded, spreading those atoms
across the galaxy.
4 billion years ago,
most of those atoms
gravitationally collected themselves
into the planet you live on,
and are made of.
Through breathing and food and water consumption,
some of the atoms in your body
are constantly interchanging
with similar atoms all around you.
You are not a fixed collection of atoms.
You are a process
that a pattern of exchanging atoms
Think of yourself as a flame,
not a thing.
A candle's flame appears to be a thing,
but it is just a process that the candle's atoms
and oxygen atoms, from the air,
keep passing through.
the flame is made of different atoms.