An Average Earth Day Used To Be Less Than 19 Hours Long (theguardian.com)

Scientists have determined that some 1.4 billion years ago, an Earth day -- that is, a full rotation around its axis -- took 18 hours and 41 minutes, rather than the familiar 24 hours. The Guardian reports: According to fresh calculations, a day on Earth was a full five hours and fifteen minutes shorter a billion or so years ago, well before complex life spread around the planet. Scientists used a combination of astronomical theory and geochemical signatures buried in ancient rocks to show that 1.4bn years ago the Earth turned a full revolution on its axis every 18 hours and 41 minutes. The number means that, on average, the length of the day on Earth has grown by approximately one 74 thousandth of a second per year since Precambrian times, a trend that is expected to continue for millions, if not billions, of years more.

Comments

Re:Moon

[MightyYar]

As long as the sun remains approximately the same mass, it should have no significant effect on the gravity felt by Earth at this distance.

Of course the sun IS losing mass, both by converting mass to energy in nuclear reactions and through boiling off particles into the solar wind.

And the Earth also experiences an influence on spin from the sun. If the sun survived long enough, Earth would become tidally locked to the sun - with a single rotation lasting an Earth year and the same side of the planet always facing the sun... the same way the same side of the moon always faces Earth. Earth is far enough away from the sun that the sun will die before this occurs. Mercury is close to the sun and is tidally locked. Venus is closer but has a bizarre backwards slow spin, the cause of I don't think is well understood.