It's a pretty broad time window: It will take 1billion years for the moon to move 10% farther away. (200K miles 0.1 / (4cm/yr)) https://www.wolframalpha.com/i

It's a pretty broad time window: It will take 1billion years for the moon to move 10% farther away. (200K miles 0.1 / (4cm/yr)) https://www.wolframalpha.com/input/?i=(distance+from+earth+to+moon)+*+0.1+%2F+4cm https://www.wolframalpha.com/input/?i=(distance+from+earth+t... Not sure how long back the 4cm/yr rate has been a good estimate.