Asha'man

At first glance, this probability chart appears to be numbers pulled at random. Notice how many values are 0.1, or 10%. This indicates a pure guess, at best.

Many of these items are not independent variables, and are really linked. For example, a whole series of numbers are based on various mineral abundances in the crust. However, given how many of these elements are formed in supernovas, they are really a single factor: the number of supernovas in the area that have contributed heavy elements to the stellar region. Multiplying these different factors together is therefore simply bogus mathematics.

Looking further, many of these numbers seem irrelevant. Life could easily evolve on a planet whose axial tilt is different than the earths. There is a large range of values that could be acceptable here, not just the single value that represents the actual tilt of the earth. “Rate of change of axial tilt?” Does he really believe that changes in axial tilt eliminate 99% of all plants from being able to form life? And how exactly is the “star’s space velocity relative to Local Standard of Rest” at all relevant? Perhaps a star could be moving so fast that interstellar collisions are a problem, but this can’t possibly rule out 95% of all stars in the galaxy, given what we know about star formation.

Looks like Ross is entirely full of it.


As for the argument about probability: there is a valid argument to be made, but this isn’t it. A planet that can support life is rare, all astronomers will agree to that. However, the size of the universe is generally considered large enough to counter that rarity. If you want to see what a real estimate looks like, do a search for the most recent updates to the Drake equation.

luvluv

Um, I couldn't understand a word in that middle link, but it shure was a purdy picture.

Should I have prefaced all this by saying I was a film major? Maybe you guys would have typed slower.

luvluv

Again, excuse my ignorance, but even if some of those items are dependant, aren't you just talking about reducing the possibility from 1 in a trillion trillion trillion trillion trillion to 1 in a trillion trillion trillion trillion?

How much of a difference would that make?

And the second link I offered explained why he claims all of these different things on the table are important.

luvluv

Here's what my boy Hugh says about the axial tilt:

axial tilt
if greater: surface temperature differences would be too great.
if less: surface temperature differences would be too great.

rate of change of axial tilt
if greater: climatic changes would be too extreme; surface temperature differences would become too extreme.

luvluv

I'm going now and I won't be back for a few days, but any answers you guys give me will be greatly appreciated.

I'll look them up after the Big East and ACC tournaments are over

I would say God bless you but I'd probably clear the room so I'll say peace.

Coragyps

Too great for what? What do you think the annual range ot temperature in South Dakota is at present?
This is just an exercise in handwaving, with an awful lot of "Goldilocks and the Three Bears" philosophy of "this one is just right" thrown in for good measure.

ps418

Ross is mostly correct in his description of the event. The fungal spike has subsequently been found in several additional P-Tr boundary sections. And in general the P-Tr extinction on land is now thought to be more severe than once thought.


However, Ross is incorrect to portray the post-extinction radiation as "rapid, widespread." In fact, one of the unique aspects of the P-Tr extinction is the delayed return to pre-extinction levels of diversity. If you look at a graph showing family-level diversity at the stage-level, such as Raup and Sepkoski (1982), you can see that marine family diversity does not return to pre-extinction values until the Jurassic (Mass extinction in the marine fossil record, Science 215, pp. 1501-3).

The entire earliest Triassic (Scythian) is characterized worldwide by large numbers of a few surviving species (typical for post-extinction periods), for instance the brachiopod Lingula, the bivalves Claraia, Eomorphis, and Unionites, the weedy plant Isoetes, and the mammal-like reptile Lystrosaurus.

Coal and reefs are absent altogether from the earliest Triassic also, resulting in reef and coal 'gaps' that are unique in the Phanerozoic. Retallack et al. (1996) argue that the ~10Ma coal hiatus reflects the gap between the extinction of peat-forming plants at the P-Tr boundary, and the appearance of new plant groups in the mid-Triassic tolerant of the dysaerobic, acidic environments in which peats accumulate. The reef gap is probably a result of both the extinction of many Permian reef framework builders (rugose and tabulate corals, for example), and the persistance of unfavorable environmental conditions.

You can refer to my article on the <a href="http://www.geocities.com/earthhistory/permo.htm" target="_blank">The Permian-Triassic Mass Extinction</a> for plenty of references and interesting tidbits.

Patrick

Asha'man

I know what axial tilt is, do you? I am saying that Ross is taking a really exaggerated position by making these factors so critical, and looses all credibility by doing so.

Do you know what the axial tilt does for us? It creates the seasons. That is all. It strongly influences the difference in temperature between summer and winter. However, around the Earth’s equator, there is virtually no seasonal change in temperature. It looks like your boy Ross is stating that life cannot exist around the equator of our planet.

He is also ignoring the fact that air and water circulate around the planet, evening out temperature extremes. Water temperature in the oceans is very stable, relative to the air. Larger planetary temperature variations would clearly be survivable, life just wouldn’t start in the most extreme portions of the planet. (Though it might eventually go there, as life has an extreme capacity to adapt to conditions.)

Do you know anything about our current understanding of planetary formation? Have you ever noticed that 99% of the large bodies (planets and large moons) in our solar system rotate in the same direction, and have a relatively low axial tilt? This is a direct consequence of how these bodies formed from a large rotating disk of dust and gas. Let me state that very clearly: all the planets formed with a low axial tilt. When we find one lone oddball planet, Uranus, with a large axial tilt, we start looking for evidence of a collision with a large body. (Smaller bodies, like asteroids and small moons, are much more likely to have odd axial tilts, since collisions with small objects are much more likely to knock them around.)

Now, how about “rate of change of axial tilt.” Ross gives this a 0.01 factor. Think about this for a moment. The earth is spinning like a top. There is an incredible amount of inertia to counter if you want this top to wobble. In fact, the Earth does wobble, on a 26,000 year cycle. However, even with this wobble, the axial tilt relative to the sun isn’t changing, it just shifts the seasons around the year, which is a non-issue. None of the other planets in our solar system are exhibiting a large rate of change in axial tilt, for exactly the same reason: inertia. How in the world did Ross decide that only 1% of all planets will be this stable? Simple: he is stupid or lying. From the evidence we have, this factor should be exactly 1.0. Since our sample size is small, and my imagination is big, I might concede a factor of 0.9999 or so, since I can conceive of a possible case where a planet might be tumbling or something. But 1%???

lpetrich

I'm not ps418, but here goes. It's possible that Earth life had been seeded by extraterrestrial visitors, perhaps time-traveling ones, understood as fellow inhabitants of our Universe.

Imagine some explorers who like exploring distant planets; one day, they visit some rocky planet with a liquid-water ocean and an atmosphere with carbon dioxide and methane in it -- enough to keep that planet from freezing over. They wander around the desolate, gray landscape of the numerous islands -- which have lots of volcanoes and lava flows and hot springs and some collision-generated mountain ranges.

They find no life there, but they leave some garbage behind near a hot spring, which eventually falls in. Some microbes from that garbage multiply in that hot spring, becoming the ancestor of all subsequent Earth life.

However, such a hypothesis is a deus ex machina that there is no positive evidence for.

So that's why scientists have preferred exploring hypotheses of spotaneous generation and chemical evolution. So far, they've had partial success.

Urey-Miller prebiotic-chemistry experiments have been widely replicated under differing conditions, and they produce a variety of organic molecules, though most of them are relatively small. Some molecules, like amino acids and nucleic-acid bases, can be produced without much trouble, but others, like sugars, are more difficult. Urey-Miller chemistry is not combined to labs, as evidence from certain meteorites, comets, and the interstellar medium reveals -- there are lots of organic molecules formed in such places.

Going in the opposite direction, the most successful extrapolation has been the RNA world -- in this hypothesis, RNA served as both information storage and catalyst, functions farmed out to DNA and proteins in most existing organisms. DNA is a modification of RNA for master-copy duty, and proteins most likely evolved out of cofactors of the RNA enzyme -- these cofactors eventually became so big that the RNA either became vestigial or disappeared.

From Urey-Miller chemistry to the RNA world is still a big jump, but I'm sure that this problem will ultimately be solved; the working out of the RNA-world hypothesis suggests that similar breakthroughs may eventually happen.

Asha'man

Nope, because you aren’t looking at the whole picture. Most of the items he lists are co-dependant with at least one other factor, sometimes dozens. By repeating this same error over and over again, he compounds the effect. This is a fundamental mistake, one that is inexcusable for a professional in a scientific field. This is a lack of understanding of basic statistics, one of the most important tools for science. Again, I can only conclude that Ross is either stupid or attempting to deliberately deceive somebody.

As for the difference, it is immense, when you add it all up. I think the current estimate for the Drake equation is around 10 ^ -20. This is a long way from the 10 ^ -161 that Ross arrived at. However, if you look at the bottom of his chart, Ross notes that there could be 10 ^ 23 planets to work with. I think this estimate is extremely low, but that leaves us with a probable outcome of around 10 ^ 3 inhabited planets. (One thousand planets!)