Extraterrestrial Life

Check this if you don't believe me.

Like most popular press shorts today, the author must have nearly broken his arm scrambling for the panic button. "Alarmist" would be a small way of putting it.

Much of what he says is somewhat uneducated. I don't know anything about the persona behind this "Great Filter" to which he continually refers, but there's no case made at all for why any one thing would be the massive impediment to anything. His lack of education on the totality of this subject is seen here: "If it happened independently twice here in our own backyard - indeed, on the only other planet we have closely examined - it must have happened millions of times across the galaxy." If life happened independently twice in the universe, here is one of the most probable places. He listed only an extremely short subset of all the requirements life has to go through in order to have a chance, so let me add a few more:

• Carbon is the most likely substance for life to form from. Other materials, such as silicon, have been suggested as possible platform sfor life, but no other atom can form the complex chains that carbon can. No one can say that it is impossible for life to be based on another substance, but it is statistically unlikely to the point of practical impossibility. For life to form, carbon must exist in abundance. For carbon to exist in abundance, there are restrictions on the sort of stars that contributed the material for a planet. Our sun and the stars in our galactic region fit the bill.
• Radiation must be balanced; a certain level of radiation is required for life, but too much of most types and even a little of other types will kill off any life. Our solar system is far enough away from the galactic core and far enough away from the center of our spiral arm that we avoid most of the radiation that the rest of the galaxy is nearly continually bathed in. Our own sun also emits more than lethal amounts of deadly radiation. Fortunately, we have a molten iron core that creates a magnetic shield around our planet to deflect the majority of those cosmic rays. That iron core appears to be the exception in planetary formation, not the rule.
• The temperature range in which life can exist is very narrow. Earth's temperatures remain fairly constant due to our very nearly circular orbit. Shifting our orbit by cosmically insignificant distances could easily make Earth far too hot or far too cold for life to form and exist. Cosmically, elliptical orbits are the rule. That nearly all of our solar system's planets are in nearly circular orbits means we are in a very odd place indeed. If the other planets besides Earth had elliptical orbits, they would affect Earth differently and pull us out of our nifty circular orbit, killing us all.
• Gravity means that cosmic collisions aren't as rare as one might expect. Fortunately, our galactically remote locale means that we have relatively few interstellar visitors. For those that do come into the solar system, our outer gas giants make a much more attractive target and soak up a lot of the travelers that might have hit earth. The objects that get by are typically slowed significantly by those planets. Many of them never get through the second level of defense, namely the asteroid belt. Our moon manages to protect us from several more impacts, either by intercepting them directly or by exerting just enough gravitational influence that the objects approach Earth at angle. That usually means these things burn up in the atmosphere.

These are just a few examples of the narrow ranges of variables that are present on Earth and our solar system but rare in the cosmos. Many of them are somewhat unique to our solar system, so if another planet exists that can support life, this solar system is the most likely location. Mars still has the lack of a molten core among other issues that make it an improbable place to find life. It is still more probable that we'd find life on Mars than in 99.9% of the rest of this galaxy. Most of the galaxies we've observed have characteristics that mean they statistically have no chance of playing host to a Sol-like solar system.

While I certainly can't say that life doesn't exist elsewhere, or that life couldn't exist in a fashion radically different from what we understand, there's nothing to suggest a single variable would be the make or break issue of life on one planet that would be of similar importance on another.