Sounds reasonable, and thanks for the source (I saw the earth-solar system etc. timeline table ... - other useful deadlines/timelines on your source too). But I mostly meant with a rough calculation, assuming noticable changes on the moon phenomenal diameter, assuming at first stage that the earth is not moving away from the Sun ... (but it does! ...). Sounds reasonable too, and it's about of the same order of magnitude as mfb's. I agree.