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November 25: The Fermi Paradox, part 2

Page history last edited by Reedcope 14 years, 2 months ago

Summary of Today's Topic

In this continuation of out discussion on the Fermi Paradox we looked at Webb's solutions from 32-49.  Solutions 32-42 tended to discuss the uniqueness of our planet's place in the universe while solutions 42-49 tended to discuss the development and intelliegence of the human race.

 

32- Life Can Have Emerged Only Recently - This solution looks at the research of astronomer Mario Livio. He has a problem with the idea that the timescales for intelligent life and the lifetime of a star are independent. There is a lot of detail about what it takes to make a planet habitable for Earth-like life. The specific conditions that Livio cites (an ozone layer) have a lot to do with conditions of the star that the planet orbits. These observations led to calculations about when life was likely to develop in the universe. Livio and others put forth from this that planetary nebulae are relatively recent, and therefore aliens have not had enough time to emerge and evolve.

33- Planetary Systems are Rare - Many previous estimates of the number of extraterrestrials, such as that by Carl Sagan, relies on an assumption that there are many planets orbiting the star, just like our solar system. However, this may not be the case. There are two theories about how exoplanets form. One, they form from a catastrophic event and two, they condense out of an nebulae. The catastrophic event theory used to be the most popular. It is based on the way that our planets and Sun currently move. This theory, however, makes the chance for exoplanets much lower because the likelyhood of two stars creating the necessary catastrophic event is decimated by the low density of stars. The nebular theory makes planetary systems much more common and has become more and more popular. The problem then became actually observing exoplanets. A new technique that looks at the "wobble" of a star detects these exoplanets. Exoplanets are still relatively few in number compared to what people had expected, but enough that the possibility of extraterrestrial life is not ruled out.

34- We are the First - Older stars don't have the elements needed to help produce life.  Our younger star does have the needed elements and was therefore able to contribute in the possiblility of life emerging on our planet.

35- Rocky Planets are Rare - Many planets are gaseus, limiting the resources for a lifeform to use inorder to develope advanced technology.  Planets with metallic ore present on them will allow for the inhabitants to utilize it and be able to develop technology.  They would be unable to construct any telescopes or radio signal emitters with which to search for other life. 

36- Continuously Habitable Zones are Narrow - A planet must remain in a habitable part of the galaxy for a very long time inorder to produce advanced life.  Continuously Habitable Zones are located within Galactic Habitable Zones, which only make up 20% of the galaxy, thus making the chance of life emerging even smaller. 

37- Jupiters are Rare - Jupiter plays a vital role in our solar system because it's eliptical orbit keeps it's gravity from overly affecting other planets.

38- Earth has an Optimal "Pump of Evolution" - Another reason that Jupiter is vital is that it's gravitational pull maintains stability in the asteroid belt, keeping asteroids from striking planets.  Other systems may not have planets that can perform the same function that Jupiter can in ours.  Jupiter must be able to direct meterorites towards a planet in its early life history and fend away meterorites from the planet later in its life history so that the planet can support life.  It must be close to the planet developing life and yet far enough away that it's orbit would not interfer with the developing planet.

39- The Galaxy is a Dangerous Place - Supernova's and gama ray bursts can send radiation for extremely large distances and wipe out life on some planets.  Supernova's are less likely to send enough radiation to sterilize the galaxy and gamma ray bursts are much more likely to be able to release enough radiation to sterilize the galaxy.

40- The Planetary System is a Dangerous Place - Asteroids and other mass extinction events can severly limit the development of life.

  • Snowball Earth - the Earth becomes engulfed in kilometer deep ice. As the suns rays attempt to warm the Earth, nearly all of the rays are reflected back into space by the ice. This creates a positive feedback system where ice covers the entire Earth. The only way to escape such a circumstance is the release of mass amounts CO2 into the atmosphere by large volcanic eruptions. CO2, a greenhouse gas, will then trap the sun's rays/heat/energy in the atmosphere, warming the Earth and melting the ice
  • Super Volcanoes - mega geological activity in the form of Super Volcanoes can tilt the balance towards having too much CO2 in the atmosphere, creating a climate too hot to sustain complex life. As Super Volcanoes spew mass amounts of CO2 into the atmosphere with each eruption, not only is heat trapped in the atmosphere, but these volcanoes can create virtual ash winters for years. The lack of sunlight penetrating through the ash, coupled with the intense heat gathering in the atmosphere creates a hostile environment for life to grow
  • Mass Extinctions - The Cambrian Extinction, Ordovicain Extinction, Devonian Extinction, Permian Extinction, Triassic Extinction, Cretaceous Extinction (end of the dinosaurs, the most famous extinction) and the current Holocene Extinction has reduced phyla of organisms and severely reduced diversity. These events throw ecosystem organization on its head, and new species come in to take the old one's place. For example, as the dinosaurs were wiped out, presumably by a meteorite striking present day Mexico, mammals were given the opportunity to rise to take their place. Had this event not taken place, the Earth would be dramatically different than how it is today.  This is a solid physical argument, albeit not testable, that could plausibly explain a lack of (current) extraterrestrial life.

41- Earth's System of Plate Tetonics is Unique - Our plate tetonics form our continents and constantly replenish the soil while acting as a thermostate for our climate.  They also create a magnetic field that protects Earth from dangerous amounts of radiation.

42- The Moon is Unique -  The moon's relative size compared to the Earth is very large. The Earth and Moon are sometimes called "The Double Planet". The moon is not the largest satellite in the solar system, but in comparison to the planet it is rotating around, it is the largest. Scientists argue that large moons in relation to their planets might be very rare. The moon affects our tides, the intensity of Earth's geological activity, and our eliptical tilt which gives us a seasonal cycle.  Many other planets in the solar system and the universe have their own moons, but Earth's relationship with its moon is very beneficial, and a parallel has not been found within our telescopic range.

43- Life's Genisis is Rare - life may not emerge from every planet. Webb defines "life" as (1) being made of cells (2) having a metabolism (3) the ability to reproduce (4) evolution

44- The Prokaryote-Eukaryote Transition is Rare - The jump from single cell organisms to multicell organisms might be very rare.

45- Toolmaking Species are Rare -  Humans might be the only species that has developed tools to use in society and to make better tools.

46- Technological Progress is not Inevitable - Even if othe species use tools, they may not be able to tranistion into advanced technological progress.

47- Intelligence at the Human Level is Rare - Maybe not every species can develope the level of intelligence that humans have.  It might be developed through convergence of evolutionary paths but we cannot be sure that it would occur again.

48- Language is Unique to Humans - The development of our brains might lend us to learnign languages.  Language use is a part of our biology.  This argument is a difficult one to make with conviction, because it is not easy to necessarily separate language from intelligence.

49- Science is not Inevitable - Science in western Europe was unique to other civilizations.  Math and other concepts might be different to other organisms.

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