Came across this brief BBC discussion of what we know about the uniqueness of Planet Earth.
A reminder that one reason why we haven’t been hearing from other civilizations in the galaxy is that there might not be any.
We might be living in a garden spot of the Universe that is much more precious than we know.
In 2000, two researchers, Peter Ward and Donald Brownlee, published a book that offered a possible explanation for our species’ apparent aloneness. It is called Rare Earth: Why Complex Life is Uncommon in the Universe (Copernicus Books, 2000). Ward, a paleontologist by training, and Brownlee, an astronomer, combined forces to produce what has come to be termed the Rare Earth hypothesis.
Simply stated, the Rare Earth hypothesis suggests that the very unique conditions of Earth that allowed complex life to arise and flourish are exceptionally uncommon — and they’re unlikely to widely occur throughout the universe.
Ward and Brownlee postulated that many fortuitous features of Earth, our Sun, and the solar system led to our highly favorable and surprisingly stable ecosystem. While some of these properties had been widely discussed in astronomy circles before, others had scarcely been mentioned.
The Rare Earth hypothesis focuses on numerous aspects of Earth and its environment that played a role in allowing complex life to develop. Some of the key factors Ward and Brownlee felt were critical to the formation of complex life included:
- A planet that exists in a favorable part of the right kind of galaxy, where significant amounts of heavy elements are available and sterilizing radiation sources are located far away.
- An orbit around a star that has a long lifetime (billions of years) but does not give off too much ultraviolet radiation.
- An orbital distance that allows liquid water to exist at or near the planet’s surface.
- An orbital distance that is far enough away to prevent the planet from becoming tidally locked to its host star.
- An orbit that is stable around its host star over cosmic timescales.
- A planetary tilt that allows for seasonal atmospheric changes to be mild, not severe.
- A solar system that includes gas giants capable of preventing debris from polluting the inner solar system, reducing the odds of major cosmic impacts and subsequent mass extinctions.
- A planetary mass large enough to both retain an atmosphere and allow for liquid oceans.
- A moon large enough to help stabilize the tilt of the planet’s axis.
- A molten planetary core that generates a significant global magnetic field, largely protecting the surface from solar radiation.
- The presence of oxygen, and the right amount of oxygen, at the right time for complex life to utilize it.
- The presence of plate tectonics, which build up land masses, create diverse ecosystems, cycle carbon into and out of the atmosphere, prevent a runaway greenhouse effect, and help stabilize the surface temperature worldwide.
In the two decades since this book was published, interest in these ideas has only grown. Last year, Astronomy caught up with both Ward and Brownlee to discuss the Rare Earth hypothesis. During those conversations, Ward recounted how the whole concept of the Rare Earth hypothesis spawned from a movie-based chat with Brownlee.
“We were just talking about how ridiculous the Star Wars bar room scene was,” said Ward.
“That’s how it all started. Look at all those aliens! You know, I just think [the notion of aliens everywhere] has been foisted on the public.”
Ward and Brownlee challenged many widely held notions that supported the idea that complex life is out there waiting to be found. For example, while astronomer Carl Sagan often opined that our Sun is an unremarkable star, in reality, about 80 to 95 percent of stars are significantly different from our own in terms of size, mass, luminosity, lifespan, and many other factors.
Furthermore, prior researchers who had attempted to answer the question of why life on Earth was so plentiful yet so rare in the universe had not included plate tectonics in their thinking at all. Indeed, an entire chapter in Rare Earth is devoted to the topic, going to great lengths to explain the role of plate tectonics in shaping Earth into a good place for life. Earth is, to the best of our knowledge, the only body in the solar system with active plate tectonics. And there are many other features of our life-friendly planet that we haven’t seen replicated anywhere else in the universe, too.
The known universe, of which we know very little
I read that, maybe ten years ago. It was good, enjoyed it. Still though, there’s that thin slice of me that holds if we aren’t so unique, if there are others ~ which in a known universe populated with billions of stars is certainly plausible ~ they may (have) take(n) an interest in us. Or not. That’s not the point, not something I want to get into
I find it interesting that some of the earliest scifi writers avoided alien life. Notable but for one fairly long short story that was pretty important to his timeline Heinlein made no mention of it across 4,000 years of his universe. Asimov was very careful in his storytelling, and actually wrote in a writers handbook I came across years ago about our wagon-trains in space mentality ~ the notion of embattled refuges fleeing tyranny across a hostile landscape through genocidal maniacs intent upon our destruction ~ preventing us from seeing what’s there. Clarke’s Odysseys very loosely suggested the possibility of life within the gasses of the gas giants, as he was blowing one up to spark new life, but most his stuff as with the others focus on humans never encountering an ‘alien’ life
I think of aliens the same way I think of angels: if they’re out there and they’re not helping us out they’re bad guys, fuck ’em. What’s really bothersome is of course here, and this notion that rather than suffer the consequences of the harm we harm have done we’ll fly off to another planet and that’s just not gonna’ happen. It’s no different than Jesus floating down out of the sky on a floating rainbow unicorn …
A lot of noise is made about the Drake Equation, a simple probability model (rate of star formation X planets per star X Goldilocks X etc.) describing the number of active communicating civilizations, but the estimates of which civilizations are within hailing distance of each other at the same time (bearing in mind the number of light years apart affects how weak the signal is, dropping off by the inverse square law) plus how slooow a conversation is over that distance, renders the probability moot.
Since the big hoo-haw that is SETI was dreamed up, our own civilization relies less and less on broadcasting, so our own window of being detected by someone else is a lot smaller than originally thought. And if a response should come back, our meat descendents would be past the point of detecting it (maybe too busy throwing rocks at each other), but an AI descendent might be willing and able to chat with them over the course of millennia.
I always worried about that “Come, Eat!” thing, which physically is something to worry about someday. In the interim there seems to be some thought that radio waves in space don’t behave as they do in here on earth and may lose more of the cohesiveness once thought to reach the stars. It maybe they won’t reach much beyond the Kuiper Belt and the outer reaches of the solar system (that we barely understand) …
That’s the same Peter D.Ward who authored the “Under a Green Sky” about mass extinctions of the past (on Earth of course), he certainly has seen how the chain of life can collapse, and understand how precious and fleeting it can be. Professor Brian Cox also echoes these thoughts about life on Earth and has given several interesting talks on it. An area that cannot be easily verified and probably never will, but at the same time traces of possible life has been discovered far away on planet k2-18b, nothing conclusive so far. Hope we survive long enough into the future, as a species, to further this line of thought and inquiry.
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Brian Cox: Life Beyond Earth Doesn’t Exist And We Are The Only Civilization
https://www.youtube.com/watch?v=bjaQDvExVeM
Terran biology may also play a big role. We have no idea how rare eukaryotic cells – needed for complex life – might be. Eukaryotic cells seem to require mitochondria, among other organelles, and they are proposed to be a prokaryotic cell ingested as food which somehow survived in a self-replicating symbiosis. I don’t think we have any idea if this is a preposterously rare event.
ET needs to be intelligent to contact us, but there does not appear to be a significant evolutionary advantage to intelligence. The oldest known species are pretty stupid or unconscious, and the smartest species on the planet appears to be rapidly self-destructive on evolutionary timescales.
Really good comment – ‘we have no idea’ is the best response to ‘is there intelligent life elsewhere in the universe?’.
Last paragraph – bonus points. There’s another theory that the Fermi Paradox exists because intelligent species have an innate propensity for self-destruction (look at ourselves – rapid environmental degradation, the ability to destroy ourselves with nuclear weapons, the possible future robot revolt, the development of lab-created killer viruses, or just simply the increasing ineffectiveness of antibiotics – the list goes on and on.)
But who knows, really. I guess maybe someone who has actually been probed knows for certain:
I always end up laughing until I choke at that.
As usual contemplation of this interesting mind exercise leaves out the importance of energy in the development of our high tech civilisation. Think for a moment how our “intelligent species” might have developed without the readily accessible hydrocarbon legacy which supercharged our economic super organism? Who knows if other potentially technological species would have access to this bonanza everyone takes for granted? We’d still be at the water wheel/windmill/sailing ship/horseback level of technology. And better for it!