Bya

bya or b.y.a. is a short way to say "billion years ago". It is used to talk about very long periods of time in the past, like in science when studying space, Earth, or ancient life. The word "billion" here means 1,000,000,000, which is the way most countries, like the US, count big numbers.

Because different places count big numbers in slightly different ways, some people might get confused. Some scientists use other words like Gya or Ga instead, but bya is still used a lot. There are also other words like mya for "million years ago", and byr for "billion years". These words usually start with a small letter, but Ga and Gya start with a big letter.