How old is the earth? how do we know?

4.54 billion yearsThe "best" age for the Earth is based on the time required for the lead isotopes in four very old lead ores (galena) to have evolved from the composition of lead at the time the Solar System formed, as recorded in the Canyon Diablo iron meteorite. This "model lead age" is 4.54 billion years

Answer the government provides "unemployment insurance"

Ba rock that formed 1,400 million years ago!