Help on a math question please!! please only answer if you know what you are doing thanks!?

I think you would basically reduce by half every 2,500 years. So at the end of 2,500 years there is 50% (100% x 1/2). At the end of 5,000 years there is 25% (50% x 1/2 or 100% x 1/2 x 1/2). At the end of 7,500 years it would be 12.5% (25% x 1/2 or 100% x 1/2 x 1/2 x 1/2) and at the end of 10,000 years it would be 6.25% (12.5 x 1/2 or 100% x 1/2 x 1/2 x 1/2 x 1/2)