That's because the Moderators hate redundant posts: The fifth planet was already posted here.
The interaction of the Earth and the Moon slows the Earth's rotation by about 2 milliseconds per century. Current research indicates that about 900 million years ago there were 481 18-hour days in a year.
I don't actually think that it's the interaction between the Earth and the Moon that slow's Earth's rotation... I think it's Commie Pinko Leftists. They keep wanting to cut the work week, for the same pay, to create 'more jobs'... and this slows progress, and since we all know that the universe revolves around them, well, I think it's plain to see, that if we don't stop the Leftists, and soon, there will be 962 9-hour days per year...