Is the Earth Special? 745
Hugh Pickens writes "Planetary scientists say there are aspects to our planet and its evolution that are remarkably strange. In the first place there is Earth's strong magnetic field. No one is exactly sure how it works, but it has something to do with the turbulent motion that occurs in the Earth's liquid outer core and without it, we would be bombarded by harmful radiation from the Sun. Next there's plate tectonics. We live on a planet that is constantly recycling its crust, limiting the amount of carbon dioxide escaping into the atmosphere — a natural way of controlling the greenhouse effect. Then there's Jupiter-sized outer planets protecting the Earth from frequent large impacts. But the strangest thing of all is our big Moon. 'As the Earth rotates, it wobbles on its axis like a child's spinning top,' says Professor Monica Grady. 'What the Moon does is dampen down that wobble and that helps to prevent extreme climate fluctuations' — which would be detrimental to life. The moon's tides have also made long swaths of earth's coastline into areas of that are regularly shifted between dry and wet, providing a proving ground for early sea life to test the land for its suitability as a habitat. The 'Rare Earth Hypothesis' is one solution to the Fermi Paradox (PDF) because, if Earth is uniquely special as an abode of life, ETI will necessarily be rare or even non-existent. And in the absence of verifiable alien contact, scientific opinion will forever remain split as to whether the Universe teems with life or we are alone in the inky blackness."
Re:But... (Score:5, Informative)
Didn't the Earth get hit by another planet, causing it to shoot a ton of crust into orbit..creating the moon?
Clearly, life requires a mars-sized object to hit the planet where life wants to form.
Jury's still out on that one: http://en.wikipedia.org/wiki/Moon_Formation#Difficulties [wikipedia.org]
Re:Life Adapts (Score:5, Informative)
FTL is in no way necessary for a technological civlization to fill the galaxy. Getting to 10% of C is plenty.
Re:Almost as if someone had designed it.... (Score:5, Informative)
Actually - if there is a God, he could have created life on an infinity of worlds, and separated all the worlds intentionally.
Yup. Every observation is compatible with the God Hypothesis.
Thus it has no predictive power. A hypothesis that "explains" anything actually explains nothing. You might as well say "something made it happen".
Re:Cop Out (Score:4, Informative)
of the 708 exo-planets so far identified, not a single one may be habitable by life.
Our methods preferentially find gas giants in close orbits.
If only one star in a billion harbors a habitable planet there will still be a couple of hundred in our galaxy, and a few trillion in the observable universe.
Re:But... (Score:5, Informative)
That's just science at work, and every theory has it's "difficulties" answering all of our questions. The fact that this particular wiki article has a "Difficulties" section doesn't disprove the scientific merit of the giant impact theory, it proves that the wiki writer tried to give a complete picture and wanted to list some of the interesting questions still out there. Simply put, the giant impact hypothesis has no rival that provides as many self consistent lines of reasoning right now.
I know that's just science at work and it's still the dominant theory, I don't have anything personal against it :P If you've been paying attention recently, however, you've no doubt noticed the mounting problems with the standard scenario. Even here at slashdot it's been discussed:
http://science.slashdot.org/story/11/08/03/1824202/earth-may-once-have-had-two-moons [slashdot.org]
http://science.slashdot.org/story/11/08/17/2247255/moon-younger-than-previously-thought [slashdot.org] ...things like this are why I said "jury's still out". Some theories are more robust than others; I wouldn't say that about special or general relativity, for example.