Rare Earth hypothesis: Why we might really be alone in the universe

C C Offline

EXCERPTS: . . . 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.

[...] It’s important to remember that the Rare Earth hypothesis only applies to the emergence of complex life. Ward and Brownlee believe that simple life, such as bacteria, is widespread in the universe — after all, even the harshest habitats on Earth harbor microbes. However, the pair feel that complex life, metazoans like animals and us, are exceptionally rare... (MORE - missing details)
Kornee Offline
The opinion space on abundance of (physical) intelligent life 'out there on other planets' is so wide it's a waste of time to take any estimate as remotely reliable. A pure 'educated guess' guessing game. Yeah that includes the Drake so-called 'equation'.
But the cited tome gels with my opinion the likes of bygone super celebrity Carl Sagan were way over their depth in cavalier pronouncements of 'a cosmos teeming with intelligent life'.
Zinjanthropos Offline
I guess that means our other worldly intelligent life detection methods are fantastic or should that be technically advanced intelligent life?
RainbowUnicorn Offline
look at the ancient stone work & building
still we cant copy that technology

if any advanced civilization is out there they will be hiding from humans.

how would the human population react to find out that there is advanced life in the galaxy but they refuse to associate with humans because humans are soo barbaric.

how would that reality change global politics ?

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