martedì 23 febbraio 2016

Le origini della vita - Panspermia

Le origini della vita - Panspermia
  • Il caso Galileo è noto ai più per la persecuzione a cui la scienza puo' essere sottoposta da parte della chiesa cattolica, eppure le teorie professate da galileo, ovvero le teorie copernicane erano insegnate anche nelle università cattoliche. Come mai tanto accanimento da un lato e tanta tolleranza dall'altro? Mi viene un possibile parallelo contemporaneo. Alcuni scienziati hanno messo in dubbio che i meccanismi dell'evoluzione siano in grado di spiegare la vita sulla terra, alcuni di loro si sono raggruppati sotto le insegne dell' Intelligent Design e il loro scetticismo è stato combattuto aspramente. Eppure il loro stesso scetticismo è condiviso anche da chi propugna l'ipotesi della paspermia come ipotesi più probabile circa le origini della vita. Al fondo c'è la medesima considerazione: l'ipotesi evoluzionistica non è in grado di spiegare la nascita della vita sulla terra. Verso gli argomenti di costoro c'è molta più tolleranza, anzi, l'ipotesi della panspermia ormai è quasi maggioritaria nell'accademia.
  • Fewer Harder Steps
  • Somewhere between 1.75 billion and 3.25 billion years from now, Earth will travel out of the solar system’s habitable zone
  • life appeared on Earth from 0.0 to 0.7 billion years after such life was possible
  • (Earth is now 4.5 billion years old.)
  • Earth being very lucky to originate intelligence life.
  • “hard steps,”like inventing life, sex, multi-cellular bodies, and intelligence.
  • the steps could have very different difficulties...if all these steps were hard.......the actual distribution of durations observed between the steps...
  • Considerazioni
  • this pushes us to give up the idea that life evolved on Earth at all, or that the origin of life was a hard step. If life evolved elsewhere, that could give a lot more time for hard steps to be achieved. After all, the universe is now 13.8 billion years old.
  • this also pushes us, if a bit more weakly, to give up the idea that the evolution of intelligence was a hard step. Intelligence seems to have appeared only 0.6 billion years after the appearance of multi-cellular animals,
  • there seems to be only room for one or two hard steps so far in the history of Earth.
  • Panspermia Confirmed
  • meteorite from Mars suggests it may show signs of life after all.   …
  • The possibility that the rock contains fossilised microbes received another boost
  • Two Kinds of Panspermia
  • Caleb A. Scharf...argument against interstellar panspermia:
  • The sequence of events involved in panspermia will weed out all but the toughest or most serendipitously suited organisms...
  • Life driven by cosmic dispersal will probably end up being completely dominated by the super-hardy, spore-forming, radiation resistant, chemical-eating, and long-lived organism.
  • if evolved galactic panspermia is real it’ll be capable of living just about everywhere.... So if galactic panspermia exists why haven’t we noticed it yet?
  • 2 scenari possibili
  • 1. Space-centered... life might mainly drift from one harsh space environment to another.... Under this scenario life must on average grow in common space environments, and so we should see a lot of life
  • 2. Planet-centered – Alternatively, space life might usually die away, and only grow greatly in special rare places like planets... effetto semi del cocco: seeds die away during ocean journeys, and then multiply on islands.
  • Scharf’s argument weighs against a space-centered scenario, but not a planet-centered scenario.
  • Pondering Panspermia
  • panspermia is no longer a marginalized view....It may not yet be the majority opinion, but it shows up often in journal articles
  • Academia is often run by an old guard ensuring that its public face reflects their old views... while younger folk quietly bite their tongues waiting for their chance
  • Most academic patrons just want to affiliate with the high status old guard,l....... no matter what its views,