As the moon goes, so go we...
The first show was "Before the Dinosaurs". I didn't see all of it, but what I did see explained at least one of the mass extinctions that occurred long before there were dinosaurs. The creatures believed to have populated the Earth hundreds of millions of years ago looked pretty fantastic. They seem to have died out because all the continents merged into one super-continent called Gwondanaland that gradually transformed into a huge desert. The worldwide drought forced animals to migrate toward the coastlands, and non-migratory creatures simply died of dehydration and/or starvation.
The next show was "Walking With Cavemen". I have no idea of how old it is, I guess maybe 2-3 years. The CGI effects were impressive and the cavemen looked good (actors in makeup and prosthetics, from what I understand). One of the neat things is that the show summarized human migration out of Africa in a way I've never really stopped and thought about.
Homo Erectus evolved in Africa, evolved into Homo Ergaster, some of the Ergasters moved out of Africa and into Asia, and became Java Man. They lasted about 1 million years.
The Homo Ergasters who remained in Africa eventually evolved into Homo Heidelbergensis, some of whom migrated to Europe and eventually evolved into Homo Neanderthalensis. The Homo Heidelbergensis who remained in Africa evolved into Homo Sapiens, some of whom migrated into Europe, Asia, and the Americas.
The show recaps speculation that long-term changes in climate gradually produced the changes in hominid groups that led to separate evolutionary paths. Severe drought conditions in Africa and severe cold in Europe caused the division of the Homo Heidelbergensis groups into two new species. Homo Neanderthalensis tended to be shorter and heavier than Homo Sapiens because those body types were better suited for the cold (meaning, a lot of Homo Heidelbergensis babies must have died from exposure while the Earth was covering itself in ice). Homo Sapiens grew taller and thinner because, as the ice formed in Europe, Africa dried up and became arid. Tall, thin body types survive better in arid conditions (meaning, a lot of Homo Heidelbergensis babies must have died from dehydration as Africa shriveled up).
Climate was also central to that portion of the second show I saw. I only watched a few minutes of it because I was tired but I sensed immediately that speculations about the origins of the moon have become very sophisticated. In "Living Without The Moon" (I think that was the title), narrated by Patrick Stewart, we are told that the moon was probably formed with a hypothetical tenth planet (Orpheus, moving in an odd orbit that took it from between Mars and Jupiter to the Earth's proximity) collided with the Earth about 4.5 billion years ago.
Computer modelling indicates that no matter how you try to form moons around the Earth, there is only one way that our moon could have been formed. The collision theory may or may not be generally accepted, but within the parameters of this theory only one stable moon could have formed. Furthermore, the formation of the moon would have been rapid (the collision would have occurred over a period of about 48 hours, it would have spread debris around the Earth that would form a ring, and the ring would coalesce into a moon in 1 to 100 years).
The debris from the collision had to settle into orbit beyond a certain distance (the name for which I didn't catch). So it is possible that several early collisions produced more debris and possibly earlier moons. However, Luna would have been formed from the last major collision between young planetary bodies involving the Earth.
The moon would have formed about 14,000 miles above the Earth. Its tidal forces would have ripped the Earth's mantle and caused huge tsunami waves to constantly roll across the oceans (and I was surprised to learn that scientists think the Earth had oceans about 4.5 billion years ago). Luna is gradually moving away from the Earth at a rate of about 1.5 inches per year. The rate must have slowed as that would mean that Luna has only moved about 106,000 miles away from the Earth in that time (unless my calculations are off).
Having a single moon in close proximity stabilizes the Earth's rotation and tilt. The Earth's rotation slowed down from about 4 hours per day to about 24 hours per day. Since the Earth doesn't wobble and since the rotation is slow, fairly stable environmental conditions for life were able to form (whereas Mars wobbles and therefore its poles melt and refreeze).
What I inferred from all this is that if we want to seek out planets not only that might support native life, but which might support us, we'll probably need to look for planets that have single Lunar bodies in orbit around them, or whose moons (in whatever combination) produce the same stabilizing effect on them that Luna produces for the Earth.
While it's true that if we can launch ships that take us to the stars we'll probably have the technology to dwell in many otherwise dangerous environments, one very real consequence of colonizing other worlds is that the colonists may lose contact with Earth for any number of reasons. If they have to sustain themselves before they can develop an industrial base to compensate for a harsh environment, they need to settle on planets that as much like Earth as possible.
That means more than just having an oxygen-nitrogen atmosphere and water. It means the planetary rotations and tilts have to be similar to Earth's.
We don't yet know what the likelihood of other star systems forming Earth-like planets in a hospitable zone, with moons that stabilize them, and which contain water, oxygen, and nitrogen really is. We're only just now beginning to identify and catalogue Earth-sized bodies in other star systems.
We might very well find planets with primitive life forms that cannot evolve into larger complex creatures simply because their planets are too unstable to support environments that nourish diversity. Despite the fact that we find microscopic life in extreme environments around the globe, complex, larger life forms need a very stable, narrow band of temperatures so that they can flourish and take advantage of abundance.