Saturday, 9 November 2013

Do we need a moon? (aka "where are the little green men?")

Orpheus hits Earth 1.0
A little while back I was discussing with my son a question that had come to mind, especially as a sailor concerned with Tides: what if we didn't have a Moon? What would that mean for the Earth?
My own thought was that we'd not have tides, of course, so the seaside waters would be rather more brackish without the swish-swoosh of the moon-driven lumps of water. And we'd not have the lunar clock-keeper of months so clearly delineated. Women's cycles -- and those of other animals --  would be different, or non-existent.
But that was about it.  Or so we thought.
But it turns out that it's not at all like that.
On Discovery Science cable TV, currently running a "Space Month" during November, they looked at this very question.  And, remarkable to me, they say at the outset that the question has only recently been considered by scientists.
Anyway, here's the news on that:
If we didn't have a Moon, we'd not be living here on Earth at all. For likely we would not have developed as Homo Sapiens.
Here's the background and the reasons:
It all goes back to the way the Moon was formed. Most likely answer: a proto-planet we now call Orpheus crashed into the earth in the early days of our Solar System, maybe 5 billion years ago.  It was a glancing blow, but devastating to both Orpheus and the then Earth, which scientists now call Earth 1.0.
The blow destroyed Orpheus, part of which was incorporated into Earth 1.0 (which thus became Earth 2.0) and part of which spun off and created the Moon.
The blow also gave earth some spin, and turned it on its axis to about 23 degrees +/- 1 degree.  This is called our obliquity, or axial tilt.
It turns out that this obliquity is critical to our earth.  It's not just that there are no seasons without obliquity.  One part of Earth 1.0 might be way too hot (100 C) and one way too cold (- 50 C) to support the development of Homo Sapiens.  Still more critical is what the Moon does to the stability of the obliquity.  For without a Moon, Earth 1.0 would have wobbled around, from 0 to 90 degrees of obliquity, over periods as short as 100,000 years, far to short to allow evolution to create Homo, Sapiens or otherwise.  A chaotic climate, unlikely to allow the stability that we know we needed to develop our civilisations.
Further: the Moon, as it drew away from the new Earth 2.0, reduced not only the range of obliquity, but also reduced the speed of spin of Earth 2.0, so that the days we now consider "normal" came into being. (The Moon is still leaving us, at about 3 cm per year).
Of course, one could argue that this is just argument form the anthropomorphic principle and that we could have or would have developed in an Earth 1.0, just developed differently.  But we don't think so.  Life, especially life of a Sapient variety, would have been immeasurably more difficult to conceive in Earth 1.0.  So say the scientists.
If that's really the case, then that might explain why we're not finding the number of Civilisations we might expect from the number of earth-like planets that we now think there may be: at least 8 billion in our Galaxy alone. And that's what Enrico Fermi asked in 1950: "where are they?"
Pity 'dat.
The Fermi Paradox: "Where are they".
Courtesy: Sean Carroll on Preposterous Universe.