The Goldilocks Zone ~ Earth's Rare Habitable Elements

More amazing stuff....



categorized under the umbrella of 'The Goldilocks Zone'....


• The Rare Earth Equation. Today the Drake Equation is being superseded by the Rare Earth Equation, as it was named by geologist Peter Ward and astronomer Donald Brownlee, both at the University of Washington in Seattle. Since the Drake Equation depends upon the number of Earth-like planets orbiting Sun-like stars, Ward and Brownlee used the latest data to revise previous estimates concerning both—and to add many once-neglected factors, now known to be critical, to the equation.

These include the fraction of stars in a galaxy’s habitable zone, the fraction of metal-rich planets, the fraction of planets with a large moon, the fraction of planets where complex animals arise (as opposed to bacteria or algae), and the fraction of planets with a critically low number of mass extinction events. In their 2000 book, Rare Earth—Why Complex Life Is Uncommon in the Universe, Ward and Brownlee remind their readers: "When any term of the equation approaches zero, so too does the final result." And they conclude: "It appears that Earth indeed may be extraordinarily rare."

Here’s why:

* Special Gas Giant. Jupiter-like planets that orbit close to their host stars, or that orbit eccentrically, refuse to politely share their space with smaller, life-harboring planets. Habitable planets need to make circular orbits within the "Goldilocks zone." Gas giants making eccentric orbits will eject smaller neighbors out of the system or send them crashing into their sun.

Well-behaved gas giants, like Jupiter and Saturn, keep circular orbits at a respectful distance. In that position, they actually serve the necessary function of cosmic vacuum sweeper, drawing comets and asteroids to themselves, rather than allowing them to hit us (as when Comet Shoemaker-Levy 9 struck Jupiter in 1995). George Wetherill of the Carnegie Institution of Washington calculated that without Jupiter, comets would strike Earth between 100 and 10,000 times more frequently than they do, meaning that "we wouldn’t be here."

• Large Moon. Habitable planets, it turns out, need to be members of a double-planet system, as some astro nomers call our Earth-Moon system. Most people don’t realize that our Moon is huge compared to the relative sizes of other moons in the planet-moon systems of our solar system. The Moon’s mass creates a stabilizing anchor for the Earth, preventing the Earth from undue attraction to the Sun or to Jupiter, which would cause the Earth to tilt too far on its spin axis.

Discovering this, astronomer Jacques Laskar wrote: "We owe our present climate stability to an exceptional event: the presence of the Moon." Without an extra-large moon orbiting at the right distance from us, scientists predict that Earth would be subject to a runaway greenhouse effect, as on Venus, or a permanent ice age, as Mars would experience if it had more water.

Worse, most astronomers now think that the presence of the Earth’s Moon is the result of a freak accident, perhaps a one-in-a-million shot, when a smaller planet hit the forming Earth with a glancing blow that allowed the mantles of each planet to combine and end up in orbit around Earth. "To produce such a massive moon," write Ward and Brownlee, "the impacting body had to be the right size, it had to impact the right point on Earth, and the impact had to have occurred at just the right time in the Earth’s growth process."

• Galactic Location. As in the real estate business, location is everything. Stars located much farther from the galaxy’s center than our Sun contain lower concentrations of heavy elements, necessary to form rocky planets like Earth. Stars much nearer the center of a galaxy reside in a denser neighborhood, exposing any orbiting planets to lethal radiation. Stars within a spiral galaxy’s arms have the same problem. Most stars traveling between the spiral arms won’t stay there, but our Sun is unusual for its circular orbit around the galaxy.

• Plate Tectonics. A hospitable planet needs a critical amount of radioactive elements, such as uranium, to produce the heat that generates a magnetic field. Without our magnetic field, the atmosphere would soon drift out into space. The radioactive core also fuels plate tectonics, the movement of the planetary crust across its surface. Of all our solar system’s planets, such movement is found only on Earth.

Plate tectonics is crucial for life, and a string of other improbable factors, in turn, prove critical to the generation of plate tectonics. These include not only a radio active core, but a crust of the right thickness and a mantle of the right viscosity, or flexibility.

• Just-Right Crust. A fortuitous assemblage of two kinds of crust are necessary, with different densities, in order to allow one to slide over the other, and to allow the lighter one to maintain itself above the water to produce stable continents.

• Timing the Warm-up. Exobiologists point out the ne cessity of a just-right host star, called a main sequence star. But main sequence stars increase their energy output over time, creating obvious problems for orbiting planets. In Earth’s case, we now know that the era when the Sun heated up was timed to coincide with the era in which Earth’s atmosphere gradually shifted from mostly greenhouse gases to the cooler mixture we enjoy today.

• Biological Contingency. Even if we assume that there are plenty of planets in our galaxy that meet the right conditions, and that life develops routinely on them, the most important question remains: How many of them will develop intelligent life? The majority of biologists and paleontologists say that evolution works without direction or a "ladder of progress." Instead, the history of life on Earth shows that the path of evolution depends upon a series of unpredictable events.

What were the odds that dinosaurs would be wiped out by an asteroid impact sixty-five million years ago, paving the way for us? What are the odds that the Cambrian explosion, when all the modern body plans appeared on our planet within a short interval, will happen on other planets?

Rare Earth’s Ward and Brownlee conclude that, though microbial life may be common in the universe, complex life (even as complex as a flatworm) is not. The Cambrian explosion of forty new, widely separated complex animal groups, they believe, didn’t have to happen. Darwinism doesn’t predict such an event. And the fact that no new major animal groups (called phyla) have evolved in the 530 million years since should give us pause.

Harvard paleontologist Stephen Jay Gould views the intelligence of Homo sapiens "as an ultimate in oddball rarity." The fact that only one species out of an estimated fifty billion developed it on this planet after 3.8 billion years of life suggests that high intelligence may not be the most natural result in the course of evolutionary events.

"If intelligence has such high value," says Gould’s Harvard colleague Ernst Mayr, "why don’t we see more species develop it?" The list of leading biologists and paleontologists on record for defending this position is impressive, including George Gaylord Simpson, Theodosius Dobzhansky, Francois Jacob, and Francisco Ayala.

British astronomer John Barrow notes that "there has developed a general consensus among evolutionists that the evolution of intelligent life, comparable in information-processing ability to that of Homo sapiens, is so improbable that it is unlikely to have occurred on any other planet in the entire visible universe."


As long as George Smoot and Paul Davies brought the possibility of God into this, what about that "miracle" option?

"Miracle," as I take it, doesn’t have to mean magical or instantaneous—but the word is up front about its demand for a nonphysical explanation. As Edwin Hubble’s protégé, astronomer Alan Sandage, told me: "We can’t understand the universe in any clear way without the supernatural."





found 3/4 of the way down the page....

[link to www.fredheeren.com]