# I Earth's early spin

1. Feb 21, 2016

### Buzz Bloom

Sorry. I lost the text of the post while trying to edit it. I will abandon this for a while.

Last edited: Feb 21, 2016
2. Feb 21, 2016

### Staff: Mentor

This text? It is still in the edit history. Without quote tags so the source code is accessible:
--------------------------
"A New Spin on the Origin of the Earth and Moon"
Astrobiology Oct 21, 2012
http://www.astrobio.net/topic/explo...new-spin-on-the-origin-of-the-earth-and-moon/ ,​
and found the following:
Many scientists believe that Earth itself emerged from a series of giant impacts. These impacts made the early Earth spin near its stability limit of about 2 hours per revolution.​

Can anyone confirm that a two hour Earth day at the approximate time of the Moon's origin is still recognized as a reasonable estimate by a substantial fraction of the scientific community?

I just complete a calculation that shows the angular momentum for the Earth with a two hour day is greater than the total current angular momentum of the system. This mean that the two hour day must refer to the Earth before the Moon's origin. I read somewhere (I can't recover where now) that the Earth's day was about one-half of the current day when the Moon formed. Can anyone cite a recent reference that gives an estimate for the Earth length of day at the time of the Moon's origin?

I found it.
From http://www.scientificamerican.com/article/moon-life-tides/
It all started some 4.5 billion years ago when, as theory has it, our nascent Earth was blindsided by a Mars-size planetary embryo, believed to have spun Earth into its initial fast rotation of roughly 12 hours per day.​

3. Feb 21, 2016

### phinds

12 hours a day for the early spin is what I've read before, 2 hours is not and seems unlikely. That statement is anecdote & opinion though so take it with lots of grains of salt.

4. Feb 21, 2016

### Buzz Bloom

Hi mfb:

Thanks much.

I did not know how to recover the text from edit history. Can you explain the procedure?

Regards,
Buzz

5. Feb 22, 2016

### Chronos

If you start a post and leave the thread before posting, you can recover it by returning to that thread and clicking on the greyed out text at the bottom of the page.

6. Feb 22, 2016

### Staff: Mentor

Do you have a "history" entry at the bottom of the post (next to "report")? If not, it is probably available to mentors only.

7. Feb 22, 2016

### Buzz Bloom

Hi mfb:

No. I don't see "history" at the bottom of my post, but thanks for the suggestion.

BTW: I think what happened is that while I was editing I was using backspace to remove some text, and
I'm guessing that I may have accidentally hit a special key, e.g. Ctrl, and that combination erased all my text in the edit area. I think it would be a useful feature to be able disable the functions that Ctrl (and other special keys) launch.

Regards,
Buzz

Last edited: Feb 22, 2016
8. Feb 22, 2016

### Buzz Bloom

Hi phinds:

The text in the Sci Am article was ambiguous, but since it is impossible for the 2 hr day to be after the moon formed, do you think it is also unlikely to be the Earth's day before the Moon formed? If so, do you interpret this article as evidence that Sci Am is not a reliable source of scientific information?

Regards,
Buzz

9. Feb 22, 2016

### phinds

Those are both inferences that I'm not willing to go to. They could be right, but I don't know that.

10. Feb 22, 2016

### Staff: Mentor

That is a browser function, the forum does not mess around with native browser functions. Ctrl+Z reverts whatever you did last in most browsers.