# How have the duration of the martian day changed in the past?

There is a panspermia theory which claims that life might have begun on Mars and I currently read a post that the human circadian rhythm is closer to the martian day length (about 25h) than the day length of Earth. I know from cave experiments that human circadian rhythm is much more complicated, but let's ignore that part and try to disprove this day length theory with physics.

I know from wikipedia that

A century ago, the average day was about 1.7 milliseconds shorter than today,[1] while in the late Neoproterozoic about 620 million years ago a day had only about 21.9±0.4 hours.

So the days on Earth slowed down significantly in the last few billion years. If this slowing down is constant, then about 4 billion years ago (when life began) a day was 10.5 hours long. I tried to find similar data about Mars, but had no luck. Can anybody help?

• Wow! It's interesting! What is all this thing? Is our planet rotating around itself more slowly as the time passes? Why? What is the physical explanation? If the angular velocity decrease, the momentum of inertia increases, for keeping the angular momentum constant. So, does the Earth become bigger in radius? I read sometime that the Earth become more flat, s.t. the equatorial radius increases. But, won't you tell us more details? – Sofia Dec 26 '14 at 22:54
• That the human circadian rhythm is longer than a human day has probably something to do with the theory of synchronized oscillators. It's much easier to synchronize an oscillator by reset than by phase comparison, but for that the oscillator has to run slightly slower than the synchronizing signal. That's a guess, of course, and I would leave it to the biologists and biophysicists to fill in the blanks. The slowing of the planet is not constant, it was much faster in the past when the moon was much closer and the tidal coupling much stronger, but you are roughly in the right ballpark, anyway. – CuriousOne Dec 26 '14 at 22:54
• @Sofia: The angular momentum is constant, but the moon is slowly moving away. This tidal coupling won't stop until the day will have the length of one month and both the moon and the earth will be tidal locked. In reality the sun will go trough its red giant phase first and destroy both before that happens. – CuriousOne Dec 26 '14 at 22:56
• @CuriousOne: Brrrrr! Our Sun will become giant red? And what about us? Where shall we go, given this curse of being limited to the light velocity? 4 light years distance to $\alpha$ Centauri. And who says that it has habitable planets? Aaaaaau! This is why I asked if there is some chance that Asimov's "jumps" be true. – Sofia Dec 26 '14 at 23:08
• @CuriousOne The gradual eating of the Sun means the Earth will be uninhabitable in only one billion year ;) – Thriveth Dec 27 '14 at 2:22