[Home] [Site map] [Updates] [Projects] [Contents; 1. Introduction; 2. Philosophy (1), (2), (3), (4) & (5); 3. Religion (1) & (2); 4. History (1), (2) & (3); 5. Science; 6. Environment (1) & (2); 7. Origin of life (1), (2) & (3); 8. Cell & Molecular (1), (2) & (3); 9. Mechanisms (1), (2) & (3); 10. Fossil Record; 11. `Fact' of Evolution; 12. Plants; 13. Animals; 14. Man (1) & (2); 15. Social; 16. Conclusion; Notes; Bibliography A-C, D-F, G-I, J-M, N-S, T-Z]
"PROBLEMS OF EVOLUTION": 6. ENVIRONMENT (3) 1. Fitness of the environment for life 2. Universe's fitness for life 3. Solar System's fitness for life 4. Earth's fitness for life 1. Circumstellar Habitable Zone (CHZ) 1. Distance from Sun 1. Just right to escape `snowball Earth' 2. Circular orbit 3.Mass 4. Moon 1. Origin 2. Effect 1. Stabilises Earth's axial tilt 2. Earth's magnetic field? 5. Water 6. Oxygen 7. Biogeochemical cycles 1. Hydrological (water) cycle 2. Carbon dioxide-silicate (rock) cycle 3. Carbon cycle 4. Oxygen cycle 5. Nitrogen cycle 6. Phosphorous cycle 7. Sulphur cycle 8. Calcium cycle 9. Sodium cycle 8. Life not extinguished in ~4 billion years
"PROBLEMS OF EVOLUTION": 6. ENVIRONMENT (3) 4. Earth's fitness for life Ernst Mayr, "the greatest living evolutionary biologist" (Gould, 2001a), "To be able to support life" planets "must be just the right distance from their sun, have the right temperature, a sufficient amount of water, a sufficient density to be able to hold an atmosphere, a protection against damaging ultraviolet radiation, and so forth" and "Furthermore ... the sequence of changes has to be just right," for example, if "there were too much free oxygen at an early stage, it would destroy life." (Mayr, 1988, p.68). "The total set of prerequisites for the origin and maintenance of life drastically reduces the number of planets that would have been suitable for the origin of life," such that "There is, indeed, the possibility that the combination and sequence of conditions that permitted the origin of life on earth was not duplicated on a single other planet in the universe." (Mayr, 1988, p.68. My emphasis) [top] 1. Circumstellar Habitable Zone (CHZ) 1. Distance from Sun"To demonstrate the idea, Dr Lunine considered three planets in the inner Solar System: Venus, Earth and Mars. The mass of a body corresponds to an ability to sustain heat flow from its interior, while distance from the Sun is correlated with the ability to retain liquid water, a driver of geological activity on Earth. Venus is about the same size as Earth. But it is so close to the Sun that any water it had must have boiled off. As such, there is no hydrological cycle and no tectonic activity, says Lunine. Mars is distant enough from the Sun to retain water. But its small size caused it to cool quickly, turning water to ice and ending large-scale geological activity. Earth occupies an intermediate position - the `sweet spot'." (Rincon P., "Titan moon occupies 'sweet spot'," BBC, 9 September 2005). [top][top]1. Just right to escape `snowball Earth'"Earth has been through many cold spells since its birth 4.5 billion years ago. Scientists say some drastic episodes froze the planet all the way to the equator. Yet these "snowball Earth" scenarios expose a gaping lack of understanding: What caused them? Lowly bacteria, according to a new study. In the first and worst snowball episode, 2.3 billion years ago, bacteria suddenly developed the ability to break down water and release oxygen. The influx of oxygen destroyed methane in the atmosphere, which had acted as a blanket to keep the planet warm. ... The idea is presented in the latest issue of the Proceedings of the National Academy of Sciences by researchers at Caltech. In modelling the scenario, the scientists say Earth's exact position from the Sun is the only thing that saved the planet from a permanent deep-freeze. ... Before the first snowball event, the Sun was only 85 percent as bright as now. But the planet was temperate, much like today. Scientists believe that's because the atmosphere was loaded with methane, a greenhouse gas. ... Then along came cyanobacteria, which evolved into the first organisms to use water in photosynthesis, releasing oxygen as a byproduct. Scientists had thought the shift might have occured perhaps as far back as 3.8 billion years ago. But the Caltech scientists searched ancient rocks for clues and found no evidence for the change prior to 2.3 billion years ago. Here's what they think happened: A regular old Ice Age set in, and glaciers advanced to middle-latitudes as they would many times in geologic history. When the glaciers retreated back toward the poles, they scoured the land and released abunant nutrients into the oceans. There were no plants or animals back then. The cyanobacteria, with their newly developed ability to make oxygen, fed off the fresh flow of nutrients, the thinking goes, and their numbers exploded. And things, well, they snowballed from there. ... "Their greater range should have allowed the cyanobacteria to come to dominate life on Earth quickly and start releasing large amounts of oxygen," said study team member Robert Kopp, a Caltech graduate student. ... Global temperatures plummeted to minus 58 Fahrenheit (-50 C). Ice at the equator was a mile thick. Most organisms died. Biology clung to hydrothermal vents or survived underground, Kopp and his colleagues say. Even today, life has shown itself to be incredibly resilient, eating rocks, swimming in boiling water and enduring thousands of years in the deep freeze. Then evolution pulled another trick, the scientists figure. Some of the organisms that did survive adapted to breathe oxygen, now that there was a lot of it. It was this ability to use oxygen that allowed life to evolve to more complex forms, the scientists say. ... That leaves the question of how we got out of that frozen mess the bacteria got us into. Eventually, the scientists say, the changed biology and chemistry caused carbon dioxide to build up enough to generate another greenhouse period. Temperatures climbed to perhaps 122 Fahrenheit (50 C) around the globe, evidence indicates. "It was a close call to a planetary destruction," says Kopp's supervising professor, Joe Kirschvink. "If Earth had been a bit further from the Sun, the temperature at the poles could have dropped enough to freeze the carbon dioxide into dry ice, robbing us of this greenhouse escape from snowball Earth." (Britt R.R., "How Lowly Bacteria Froze Earth Solid," Livescience, 1 August 2005). [top]2. Circular orbit [top] 3."Also vitally important is a planet's mass. A planet's habitability depends on its mass in many ways; terrestrial planets significantly smaller or larger than Earth are probably less habitable. Because Its surface gravity is weaker, a less massive Earth twin would lose its atmosphere more quickly, and because of its larger surface-area-to-volume ratio, its interior might cool too much to generate a strong magnetic field. And as we will show in Chapter Five, smaller planets also tend to have more dangerously erratic orbits. In contrast, without getting more habitable, a more massive Earth- twin would have a larger initial inventory of water 14 and other volatiles, such as methane and carbon dioxide, and would lose less of them over time. Such a planet might resemble the gas giant Jupiter rather than our terrestrial Earth. In fact, Earth may be almost as big as a terrestrial planet can get. While life needs an atmosphere, too much atmosphere can be bad. For example, high surface pressure would slow the evaporation of water and dry the interiors of continents. It would also increase the viscosity of the air at the surface, making it more difficult for big- brained, mobile creatures like us to breathe. In addition, more surface gravity would create less surface relief, with smaller mountains and shallower seas. Even with more vigorous tectonic churning, rocks could not support mountains as high as those we enjoy. The planet probably would be covered by oceans and too mineral-starved at the surface (and too salty throughout) to support life. Even a gilled Kevin Costner, cast as a lone mariner, would find such a waterworld unappealing. To add insult to injury, the surface gravity of a terrestrial planet increases with mass more rapidly than you might guess. Intense pressures compress the material deep inside, so that a planet just twice the size of Earth would have about fourteen times its mass and 3.5 times its surface gravity. This higher compression would probably result in a more differentiated planet; gases like water vapor, methane, and carbon dioxide would tend to end up in the atmosphere. Earth has kept dry land throughout its long history, in part, because some of its water has been sequestered in the mantle; in contrast, a more massive planet would probably have degassed more than Earth. Maybe you're still pining away for some adventure on a sci-fi-inspired giant terrestrial planet, but there's another problem with larger planets impact threats. To put it simply, they're bigger targets. Asteroids and comets have a really hard time avoiding larger planets, so these planets suffer more frequent, high-speed collisions. While their bigger surfaces distribute the greater impact energy over more area, this doesn't compensate for the larger destructive energy, since surface area increases slowly with mass for terrestrial planets more massive than Earth." (Gonzalez G. & Richards J.W., "The Privileged Planet: How Our Place in the Cosmos is Designed For Discovery," Regnery: Washington DC, 2004, pp.59-60)Finding 'Super Earth' is a 'Goldilocks' errand, USA Today, February 19, 2006, Dan Vergano ... Astronomers have detected more than 150 planets orbiting nearby stars, raising hopes of finding another Earth, not only for the Star Trek crowd but also among sober-minded scientists and NASA administrators. But there may be more to finding that "goldilocks" planet, just the right size and distance from its star to match Earth, warns one research team. Last month, an international team reported in Nature that it had detected the smallest extrasolar planet orbiting a normal star yet. Just over five times heavier than Earth, OGLE-2005-BLG-390Lb, is 28,000 light years away. It orbits two-and-a-half times further away from its star than Earth does the sun, and enjoys chilly temperatures of -364 degrees because of the dimness of its star. A few earlier discoveries of similarly-sized "extra solar" planets had also occurred, but all those orbit very close to their stars. But the discoveries show that astronomers are closing in on a planet in the "habitable zone" where temperatures are neither too cold or too hot for life, suggest researchers like Princeton's Bohdan Paczynski, one of the discoverer's of the latest planet. But it may not be so easy, suggests University of Minnesota physicist Renata Wentzcovitch and colleagues in the current Science magazine. For "Super Earth" planets only a few times heavier than Earth, the interior chemistry of the planet's core may have a big effect on whether future space tourists will ever want to vacation there. In the study, the team looked at the "Super Earth" orbiting the star Gliese 876, 15 light years away. The researchers analyzed the chemistry of perovskite, an electronically inert mineral made of oxygen, silicon and magnesium, found in the mantle covering the iron cores of planets. On Earth, there is a thin layer of the stuff in the mantle. Through computer simulations, the study team found the extra gravity of a "Super Earth" (twice as strong on its surface as Earth's) would crush these minerals into new forms, ones that would take on the properties of semi-conductors or metals, Wentzcovitch. So what? The result there would be enhanced heat flow from the planet's core to the surface, which means more volcanoes and more "planetquakes." The effects on the planet's magnetic field, which on Earth shields the surface from solar radiation, of increased electrical activity in the mantle are more difficult to figure out, she says. The larger point is there is more to finding another Earth than detecting a planet the same size and same distance from its star, she says. Venus and Earth are very similar, she notes, but have significant differences in their interior chemistry. Venus has a more viscous interior that lead to a planet- sized earthquake hundreds of millions of years ago, she says, and that likely also explains the hellish conditions there, where 800-degree winds are lashed by sulfuric acid rain. ...4. Moon 1. Origin "The leading theory for the Moon's formation has a Mars-sized object slamming into Earth about 4 billion years ago, shortly after our planet formed" (Britt., 2004d). "The evidence is partly in the Moon's composition, which is similar to the upper portions of Earth." (Britt., 2004d). "The Moon is generally believed to have formed from debris ejected by a large off-centre collision with the early Earth" (Canup R.M. & Asphaug E., 2001). "The giant impact theory suggests that an object roughly the size of Mars crashed into Earth 4.5 billion years ago, throwing up vast amounts of debris that then aggregated into the Moon " (Macleod, 2003). "The theory has been supported by the similar composition of Earth and Moon rocks, but the probe should find that the Moon contains less iron than Earth, compared with lighter elements such as magnesium and aluminium " (Macleod, 2003). "This theory, that the Moon's core is less massive than the Earth's, has also been used to explain the Moon's orbit around the Earth, which is inclined by around 10 degrees relative to the equator " (Macleod, 2003). "Most other planetary satellites in the solar system have orbital inclinations less than 1 or 2 degrees " (Macleod, 2003). "The Moon was blasted away from the early Earth by a massive interplanetary collision, according to an idea which has received strong new support" (Whitehouse, 1999a). "The new data comes from the Lunar Prospector spacecraft" (Whitehouse, 1999a). "This is a critical finding in helping scientists determine how the Earth and the Moon formed" (Whitehouse, 1999a). "The new results show that the lunar core contains less than four percent of its total mass" (Whitehouse, 1999a). "This is a very small ratio compared to the Earth - its core has about 30 percent of the planet's mass" (Whitehouse, 1999a). "The size of the core is critical because everything in the solar system was made from the same starting materials" (Whitehouse, 1999a). "As the early Earth formed, the heavy iron sank to the core, leaving a rocky layer above" (Whitehouse, 1999a). "If the Moon had started as an independent planet, it too would have a large iron core" (Whitehouse, 1999a). "However, the Moon's small core suggests it is a chunk of rock knocked out of the early Earth, after most of the iron there had separated out" (Whitehouse, 1999a). "The collision theory suggests that a planet about the size of Mars struck the ancient Earth" (Whitehouse, 1999a). "It would have almost disintegrated both planets and left huge clouds of debris orbiting what remained of the Earth" (Whitehouse, 1999a). "This impact occurred after the Earth's iron core had formed, so it ejected rocky, iron-poor material from the outer shell into orbit" (Whitehouse, 1999a). "It was this material that collected to form the Moon" (Whitehouse, 1999a). " "A dark, lifeless object less than half as massive as Earth careens around a newborn Sun" (Britt, 2001a). "Eventually, the nameless protoplanet meets up with a fledgling Earth" (Britt, 2001a). "It is not a head-on collision, but rather a glancing blow" (Britt, 2001a). "The impact imparts what astronomers call angular momentum into the system" (Britt, 2001a). "It sets Earth to spinning on its axis and creates a Moon that would go round and round the host planet for billions of years" (Britt, 2001a). "The shock of the impact strips material from the outer layers of Earth and the impacting object" (Britt, 2001a). "The mostly iron cores of both bodies meld into Earth's core" (Britt, 2001a). "It is like a compact car merging onto the highway and colliding with an S.U.V-- glass, trim and hubcaps fly, but the two chassis remain hopelessly tangled" (Britt, 2001a). "All told, about 2 percent of the combined mass of the objects -- mostly rocky stuff that's largely bereft of iron -- begins to orbit the Earth" (Britt, 2001a). "About half of this eventually becomes the Moon" (Britt, 2001a). "Some of the stripped material is heated so fantastically that it vaporizes and expands into the surrounding vacuum of space" (Britt, 2001a). "`The material that was vaporized expands into a cloud that envelops the whole planet" (Britt, 2001a). "Meanwhile, a long arm of solid matter is winging its way around Earth" (Britt, 2001a). "Some of it develops into a clump that slams back into the planet" (Britt, 2001a). "The rest is flung into orbit, all pretty much along a plane that mimics the path of the incoming object" (Britt, 2001a). "This plane slices through what is now Earth's equator, and it is roughly the same plane along which the Moon orbits" (Britt, 2001a). "`The object came in and hit, and that's what set the Earth's rotation and what its equator would be" (Britt, 2001a). "`For the first time, we demonstrated with simulations that a single impact can give you an iron-depleted Moon of the right mass, and the current mass of the Earth, and the current angular momentum of the Earth-Moon system" (Britt, 2001a). "Though the model covers only a day's time, Canup said shortly thereafter the material in outer regions began to cool" (Britt, 2001a). "Gradually, small clumps would have formed, collided with one another, and grown" (Britt, 2001a). "Based on other models, she said it would have taken between 1 and 100 years to make a Moon after the impact" (Britt, 2001a). However, "if an object the size of Mars hit the young Earth about 4.5 billion years ago, it would have splattered a lunar mass of material into orbit" and "because the disc was so spread out, only 20 to 50 per cent of the initial disc material would form the Moon--the rest would fall back to the Earth." (Hecht, 1997). "You need to produce a much larger disc initially because you lose most of the material back onto the Earth." (Hecht, 1997). "the object that hit the Earth would have to contain 2.5 to 3 Martian masses to create a big enough disc" (Hecht, 1997)."The impact orientation and size are constrained by the angular momentum contained in both the Earth's spin and the Moon's orbit, a quantity that has been nearly conserved over the past 4.5 billion years" (Canup R.M. & Asphaug E., 2001). "But the model shows that the impact would have left the Earth-Moon system with over twice its present angular momentum." (Hecht, 1997). "Explaining how all that angular momentum dissipated is very difficult" (Hecht, 1997). "Simulations of potential moon-forming impacts now achieve resolutions sufficient to study the production of bound debris" (Canup R.M. & Asphaug E., 2001). "However, identifying impacts capable of yielding the Earth- Moon system has proved difficult" (Canup R.M. & Asphaug E., 2001). "Here we report a class of impacts that yield an iron-poor Moon, as well as the current masses and angular momentum of the Earth-Moon system" (Canup R.M. & Asphaug E., 2001). "This class of impacts involves a smaller-and thus more likely- object than previously considered viable, and suggests that the Moon formed near the very end of Earth's accumulation.(Canup & Asphaug, 2001)"Computer simulations gave new life ... to a theory that has intrigued astronomers for years: the idea that one big collision between the Earth and a Mars-sized planet gave birth to the moon" (Zabarenko, 2001). "The so-called "giant impact" theory was first envisioned in the 1970s, but now scientists ... have put together a scenario that would account for the moon's creation as well as the fact that a day on Earth is 24 hours long" (Zabarenko, 2001). "The previous models of the impact theory had identified impacts capable of producing the moon, but they were unable to account for all of these features of the Earth-moon system simultaneously" (Zabarenko, 2001). "By showing that just one impact can do the job, what we're doing in effect is demonstrating a more probable scenario" (Zabarenko, 2001). "The new research, presented in the current edition of the journal Nature, postulates an enormously energetic but oblique crash between Earth and a planet the size of Mars, which is about half Earth's size" (Zabarenko, 2001). "The energy unleashed by this collision some 4.5 billion years ago would have been enough to destroy the incoming planet and melt Earth all the way through" (Zabarenko, 2001). "There would also have been some vaporized rock debris kicked up from the crash, which would start orbiting Earth" (Zabarenko, 2001). "Once the orbiting debris cooled, it's from that stuff that the moon then coalesced" (Zabarenko, 2001). "The whole process, from collision to formation of the moon, took less than 100 years" (Zabarenko, 2001). "The glancing angle of the collision -- perhaps 40 degrees or so -- caused Earth to start spinning, but much faster than it does now" (Zabarenko, 2001). "In those early times, an Earth day would have lasted only five hours" (Zabarenko, 2001). "The moon was also thought to be much closer to Earth than it is now; in fact, the Earth and the moon continue to get more distant from each other by several inches (centimeters) a year" (Zabarenko, 2001). "As the moon moved away from Earth, Earth's rotation slowed" (Zabarenko, 2001). "The planet that caromed into Earth is long gone, one of a dozen or more mini-planets in the process of formation that never quite made the grade in our solar system" (Zabarenko, 2001). "Most of these miniplanets were about Mars' size, providing plenty of candidates" (Zabarenko, 2001). "Everything has really come together, because it looks like the type of impact you need to explain the Earth's mass and initial spin rate also tends to naturally place a sufficient amount of material into orbit to form a moon with the size of our moon" (Zabarenko, 2001). "The mysterious tilt of the Moon's orbit around the Earth is probably due to the satellite's violent origin" (Whitehouse, 2000a). "A team of researchers have used a computer model to trace the Moon's orbit back in time" (Whitehouse, 2000a). "The Moon, scarred by impacts itself The study suggests that the gravitational interaction between the forming Moon and the disk of debris from which it emerged was responsible for putting the body in its present orbit" (Whitehouse, 2000a). "Popular theory has it that the Moon formed violently and quickly" (Whitehouse, 2000a). "Approximately 4,500 million years ago, when the Solar System was young, a so-called proto-planet, probably about the size of the present-day Mars, smashed into the young Earth with incredible violence" (Whitehouse, 2000a). "Within minutes, a jet of vaporised rock was blasted into space and begun to settle around the Earth forming a disk" (Whitehouse, 2000a). "Within hours, the entire Earth's surface, already hot, had melted" (Whitehouse, 2000a). "Computer simulations of the event suggest that the lunar orbit should have been nearly aligned with the Earth's equator, with only about a one degree tilt" (Whitehouse, 2000a). "The problem is that the Moon's orbit is much more tilted - about five degrees" (Whitehouse, 2000a). "This is unusual because most other planetary satellites in our Solar System have orbital inclinations smaller than one or two degrees" (Whitehouse, 2000a). "The cause of the Moon's large orbital tilt has long been a mystery" (Whitehouse, 2000a). "The inclination problem had been one of the last remaining obstacles for the impact hypothesis of Moon formation, says Dr William Ward" (Whitehouse, 2000a). "His team believes the Moon acquired its large tilt soon after it formed because of a gravitational interaction with the other debris left over from the impact event" (Whitehouse, 2000a). "Computer simulations of the giant impact suggest that about two lunar masses of material were put into an Earth-orbiting disk" (Whitehouse, 2000a). "In the model, debris particles in the inner regions of such a disk are prevented from coalescing by Earth's gravity, which tends to pull objects apart" (Whitehouse, 2000a). "Gravitational interaction The Moon forms in about a year at the outer edge of the debris disk, at a distance of about 22,500 kilometres (14,000 miles) from the Earth" (Whitehouse, 2000a). "The key point is that after the Moon coalesced, its gravity would generate waves in the inner disk" (Whitehouse, 2000a). "The gravitational interaction of the Moon with these waves would then modify the young Moon's orbit" (Whitehouse, 2000a). "The computer model simulated the interaction of the Moon and the inner debris disk, assuming that the Moon formed in an orbit with only a one degree tilt" (Whitehouse, 2000a). "They found that the interaction of the young Moon with the disk can amplify the lunar inclination to as much as 15 degrees" (Whitehouse, 2000a). "This theory explains the Moon's anomalous orbital tilt as a natural consequence of its formation from a giant impact event. (Whitehouse, 2000a). "The Moon could have been created in a double-whammy impact 4.5 billion years ago" (Pease, 2003). "The event was the culmination of a 100-million-year process in which the Earth and its neighbouring planets were built through cosmic collisions between sub-planetary objects" (Pease, 2003). "According to Dr Robin Canup, a proto-planet, something like the size of Mars, collided at high speed with an Earth that was nearly fully formed" (Pease, 2003). "The collision was a glancing one" (Pease, 2003). "It shattered our Earth, but pulverised the incoming planet" (Pease, 2003). "Simulations show the impactor being sprayed out into a shower of orbiting debris" (Pease, 2003). "But within a matter of hours, much of this had re-grouped to form a new impactor that smashed into the Earth's surface a second time" (Pease, 2003). "At this point, the impacting object was destroyed" (Pease, 2003). "Most of the impactor rained down on to, and became incorporated into, the Earth - the last major component to be integrated into our planet" (Pease, 2003). "But 10% or so of the mass was spread out into an incandescent disc around the Earth - a scorching equivalent of Saturn's rings" (Pease, 2003). "It was out of this material that the Moon was formed in a matter of decades" (Pease, 2003). "At the time it was 15 times closer than the Moon is now" (Pease, 2003). "Anything that had happened geologically to the Earth before that would have been erased by the impact" (Pease, 2003). "The planet's surface was probably melted down to a depth of 1,000 kilometres, cloaking the Earth in a "magma" ocean that would have radiated like a red-hot furnace" (Pease, 2003). "The precise date the Moon was formed is still a matter of debate, but Dr Canup's research implies it was right at the end of the planet- building process, which could have taken up to 100 million years" (Pease, 2003). "Curiously, recent chemical research has shown that the planet Earth collided with was a twin to the Earth - scientists have called it "Theia" after the mother of the Moon in Greek mythology" (Pease, 2003). "Details in the chemistry of the Moon show it to be almost identical in some key respects to the Earth, although it was made almost entirely from remnants of the impactor" (Pease, 2003). "Theia must have been formed in an orbit almost identical to the Earth's" (Pease, 2003). "As Robin Canup points out, the Moon- forming impact gave the Earth its spin on its axis that now gives us 24-hour days, and stirs up the atmosphere so that no part of the Earth is too hot or too cold for life" (Pease, 2003). "And the presence of the Moon gives the Earth a kind of gravitational counterbalance that stabilises its slightly inclined axis of rotation - 23 degrees to its orbit - that gives us the congenial cycle of the seasons over a single orbit around the Sun" (Pease, 2003). "And the scalding magma ocean, according to Mike Drake, was (surprisingly) the place where the water of the Earth's oceans would have been held - giving our planet one of its key ingredients for life. "The formation of the Moon must have occurred during the first 30 million years of the life of the Solar System Until now, its core was thought to have arisen over the course of 60 million years" (BBC, 2002a). "The evidence comes from revised radioisotope dating of meteorites, the remnants of the stuff that made the planets" (BBC, 2002a). "The data also has implications for the genesis of the Moon" (BBC, 2002a). "The Moon was thought to have arisen after an impact between the burgeoning Earth and a planet at least as massive as Mars" (BBC, 2002a). "One theory is that the Earth was half-made when it collided twice with a body double the mass of the Red Planet" (BBC, 2002a). "Another assumes it was about 90% of its current dimensions when it was struck by a Mars-sized object" (BBC, 2002a). "Both collisions could, in theory, have produced a big enough impact to blast enough debris into space to form the Moon" (BBC, 2002a). "But since the Earth took 100 million years to reach something like its present size, the first option is more likely" (BBC, 2002a). "The data is based on measurements of radioactive nuclei in meteorites" (BBC, 2002a). "The ratio of the radioactive elements hafnium and tungsten in these very primitive rocks was compared with rocks on Earth and Mars" (BBC, 2002a). "We conclude that core formation in the terrestrial planets and the formation of the Moon must have occurred during the first 30 million years of the life of the Solar System" (BBC, 2002a). "Researchers think the impact involved low relative speeds -- like one car merging into another on the freeway rather than a more destructive head-on collision." (Britt., 2004d). "For that to happen, the impactor must have formed nearby in an orbit similar to that of Earth" (Britt., 2004d). One theory is that "The Mars- sized impactor formed at the same distance from the Sun as Earth in a gravitationally stable spot known as a Lagrangian point, then drifted out of that birthplace -- thanks in part to collisions" (Britt., 2004d). "There are five Lagrangian points related to the Earth, Moon and Sun, and each has some gravitational stability" (Britt., 2004d). "The Lagrangian points named L4 and L5 sit along Earth's circular path around the Sun. ... mov[ing] as Earth moves" (Britt., 2004d). Each forms an equilateral triangle between itself, the Sun and Earth. Gravity from the Sun and Earth combine to create a state of equilibrium at each of the two points." (Britt., 2004d). "If material flew in there and slowed down a lot by collisions with other objects near these locations, the material would stay, and start to accumulate by gravitational attraction and mutual frictions." (Britt., 2004d). "As initial rocks grow larger, into what scientists call planetesimals, more material is attracted" (Britt., 2004d). "After about 30 million years a Mars-sized object results ... wandering around the L4 region, in a random walk fashion as it is impacted or nearly impacted by planetesimals" (Britt., 2004d). "Its velocity gradually increases with respect to L4" (Britt., 2004d). "At about 30 million years its velocity is sufficient for it to just barely leak out of the L4 region of stability" (Britt., 2004d). "The object moves along a path similar to Earth's orbit but at a different speed" (Britt., 2004d). "Its movement is chaotic because the Sun and Earth are tugging on it roughly equally" (Britt., 2004d). "It will approach the Earth either from behind (if it has to catch up), or from the front" (Britt., 2004d). "Once it leaves the L4 vicinity and starts creeping, it can take a few years to reach the Earth" (Britt., 2004d). "From there, other researchers have detailed how the impacting object turned a chunk of Earth's rock into hot vapor and flung it into space. Some of that orbited the planet and eventually coalesced to form the Moon" (Britt., 2004d). However, the "Lagrangian points" are 'locations in space where a small body can maintain a stable orbit despite the gravitational influence of two much more massive bodies, orbiting about a common centre of mass" (Illingworth, 1994, p.245. My emphasis). They are "points ... in the orbital plane of two massive objects circling about their common centre of gravity where a particle of negligible mass can remain in equilibrium" (Mitton., 1991, p.219. My emphasis). "A Lagrangian point 60° ahead of Jupiter in its orbit around the sun, and another 60° behind Jupiter, are the average locations of members of the Trojan group of asteroids; these points are denoted L4 and L5" (Illingworth, 1994, p.245). "The Trojan asteroids, which share the orbit of Jupiter, are examples of masses trapped at the two stable Lagrangian points in an orbit" (Mitton, 1991, p.219). "A quite remarkable aspect of the Moon is that its formation appears to have been highly unlikely, a rare chance happening" (Ward & Brownlee, 2000, p.229). " Impact origin of the Moon as modeled by Cameron and Canup (1998)" (Ward & Brownlee, 2000, p.231). " A body several times more massive than Mars impacts the edge of the half-grown Earth with spectacular effects" (Ward & Brownlee, 2000, p.231). " After a glancing blow, the two distorted bodies separate and then recombine" (Ward & Brownlee, 2000, p.231). " The metallic cores " (Ward & Brownlee, 2000, p.231). " of both bodies coalesce to form Earth's core, while portions of the mantles " (Ward & Brownlee, 2000, p.231). " of both bodies are ejected into orbit and accumulate to form the Moon" (Ward & Brownlee, 2000, p.231). " After its formation the Moon spiraled outward, a process that continues to the present time" (Ward & Brownlee, 2000, p.231). " To produce such a massive moon, 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" (Ward & Brownlee, 2000, p.231). [top] 2. Effect 1. Stabilises Earth's axial tilt"Earth's uniquely large moon, relative to its own size, among the planets, is been a major in stabilising the Earth's obliquity (axis tilt) and so preventing of the environment from swinging too far out of line leading to runaway "icehouses" or "greenhouses": "Without the moon, however, the earth's obliquity would oscillate, even more than that of Mars, leading to far greater climatic instability than we presently experience and endangering the course of biological evolution" (Hammond, 1975). "At the same time our existence depends on an unusually large moon since its pull stops the Earth wobbling around too much on its axis and causing wild and catastrophic swings in climate like those on Mars" (Chown, 1999). And "since the existence of such a relatively large moon appears to be a statistically unlikely occurrence, most other proto- Earths in the universe may not likewise have been so fortuitously saved. Our Earth looks, then, more and more unique-and therefore precious" (Oberg, 1981, pp.75-76). [top]"A billion years ago, the Moon was much closer to Earth than it will be tonight. Its tighter orbit meant it needed just 20 days to go around us, to make a lunar month. Other things were noticeably different, too. A day on Earth back then was only 18 hours long. People were probably wishing, "If only I had 24 hours in a day" Okay, there were no people then, but the critters of the time eventually got their wish. In the intervening eons, the Moon has been drifting away. Each year, it moves about 1.6 inches (4 centimeters) farther into space. It is a coincidence of orbital and species evolution that we humans are on this planet during an era when we can work 24/7, should that be demanded. Also by coincidence, we're here when the Moon's apparent size in the sky is equal to that of the Sun, so that a total solar eclipse is possible. Furthermore, we arrived comfortably after the pockmarked satellite began showing just one face to Earth, providing that immutable and unchanging beacon we call a full Moon, cosmic governor of terrestrial love and a lot of loony ideas. Or, one could argue, none of this is coincidence at all. If not for the Moon, some say, love as we know it would never have happened and we wouldn't be here to contemplate Earth's orbiting treasure. The Moon has had dramatic effects on our planet and the life that inhabits it, researchers believe. The Moon stabilizes Earth's rotation, for example, preventing otherwise dramatic movements of the poles that would fuel climate swings that some scientists figure might have doomed any chance for life to form, let alone evolve. And biologists speculate that tides, generated mostly by the Moon, would have been a logical place for life to originate. Sea creatures might have then used tidal regions as experimental sites for testing the habitability of land, and therefore as an excuse to develop lungs. Put short, your gilled ancestors might have used the Moon like a gravitational guiding light to the first non-aquatic procreation. In that sense, the only coincidence in all this is the fact that the Moon ever came to exist in the first place. For there was a brief time in the early history of our planet, likely 100 million years or less, when there was no Moon in the sky." (Britt R.R., "Moon Mechanics: What Really Makes Our World Go 'Round," SPACE.com, 18 March 2003). [top]2. Earth's magnetic field?"Scientists speculated today on a solution to a longstanding mystery of why the Moon is overloaded with nitrogen. It came from Earth, they say. If the idea is correct, then the Moon could serve as an attic of information that could reveal when Earth's magnetic field was jumpstarted shortly after the planet formed. Let's go back 4.5 billion years. The Moon is thought to have formed when a Mars-sized object slammed into Earth in a glancing blow that kicked up a bunch of superheated material. The stuff orbited Earth, cooled, and condensed into a satellite. It was all so hot that nitrogen and other so-called volatile elements didn't survive, theoretically leaving the Moon bereft of them. But examinations of lunar soil brought back by Apollo astronauts finds plenty of nitrogen. Some would have arrived on the solar wind, but there's more than the Sun ought to have contributed. It's possible the lunar nitrogen arrived via interplanetary dust. But that idea hasn't been proved, nor are the potential quantities pinned down. The Moon was closer In the Aug. 4 issue of the journal Nature, Minoru Ozima of University of Tokyo and colleagues put forth an intriguing alternative The new scenario is based on the possibility that Earth's magnetic field was not born with the planet 4.5 billion years ago, but developed sometime thereafter when the molten iron core took on a "differential rotation," meaning the outer and inner parts of the core rotate at different rates. Nobody knows exactly how or when all that developed. The magnetic field serves as a protective shield, blocking many (but not all) of the charged particles that stream in from the Sun and keeping cosmic rays largely at bay, too. It also helps prevents Earth-bound particles from escaping willy-nilly into space. Before the magnetic field formed, nitrogen molecules in Earth's atmosphere broke down into nitrogen ions, and ions in the outer atmosphere escaped freely to the Moon, Ozima's team figures. Back then, Earth and the Moon were much closer than they are today, so it would have been easier for the satellite's gravity to lure the ions in. If that's the case, then scientists should be able to find out when the magnetic field turned on by checking if the amount of nitrogen is significantly higher in lunar soil of a particular age." (Britt R.R., "Earth's Air Trapped in Moon Dirt, Scientist Speculates," SPACE.com, 3 August 2005)."Cambridge, England - Just half a lifetime ago, Mars was seen as Earth's sister, a future home-from-home, possibly also a rival the Red Planet, where loathsome aliens plotted invasions of our home. Then, in the 1960s, came the hammer blow. Blurry pictures sent back by early space probes depicted Mars as a terrifying orange desert, parched and dusty, clearly incapable of nurturing any life. The fourth rock from the Sun suddenly seemed to be just that: a rock. ... No one should be tempted to revive any of the verdant fantasies of sci-fi, for no sign has emerged yet of life on Mars, past or present. ... Most of Mars' volcanic activity petered out around 1.5 billion years ago, but carried on in some areas until as recently as two million years ago ... One theory is that around 3.5 billion years ago, the planet somehow lost its core-driven magnetic field, a shield that protected it against the fierce buffeting of particles from the Sun. Without this, the planet's thick carbon dioxide atmosphere was progressively shredded by the solar wind and its precious oceans slowly evaporated." (Ingham R., "Slowly-dying Mars still holds surprises," Independent Online, September 08 2005) [top]5. Water One of the prerequisites of life is "a sufficient amount of water" (Mayr, 1988, p.68). The Earth has an estimated 1.3 billion cubic kilometres of water on Earth, which has existed in essentially its present volume for the last 3.8 billion years (Bryson B., 2003, p.240). The Earth's ocean basins have "just about the right amount of water to fill them" (Clark, 1961, p.90). If Earth had too much water, there would be no land and then not only could there not be land plants and animals, but there would not be shallow seas (Ward & Brownlee, 2000, p.264) with their nutrient-rich land-sea interface (Ward & Brownlee, 2000, p.206). If the Earth was a "water-world" there would be far fewer (if any) marine plants and animals (Ward & Brownlee, 2000, p.206). On the other hand, if the Earth had too little water, the earth's temperature extremes would be too wide for complex life to arise and survive (Ward & Brownlee, 2000, pp.264-265). But in fact, "It appears that Earth got it just right" (Ward & Brownlee, 2000, p.265. My emphasis). "This establishes a rather stringent requirement for ... life: It needs a stable temperature for billions of years so water can remain in a liquid state" (Naeye, 1996, p.39). [top] 6. Oxygen"Does life exist elsewhere in the Universe? This question continues to puzzle scientists, but now Professor David Catling at Bristol University thinks that significant oxygen in the atmosphere and oceans of a distant planet are required for complex organisms to evolve. The fact that it took almost 4 billion years here on Earth means that other planets might not have a lot of time to evolve complex life. Since our Sun still has another 4 billion years before it dies, life has time to flourish, but planets around other, more short-lived stars might not be so lucky. ... NASA Pathfinder mission exploring the surface of Mars. Image credit: NASA/JPL. Click to enlarge. Whether life exists on other planets remains one of the great unanswered questions of science. Recent research argues that an atmosphere rich in oxygen is the most feasible source of energy for complex life to exist anywhere in the Universe, thereby limiting the number of places life may exist. Professor David Catling at Bristol University, along with colleagues at the University of Washington and NASA, contend that significant oxygen in the air and oceans is essential for the evolution of multicellular organisms, and that on Earth the time required for oxygen levels to reach a point where animals could evolve was almost four billion years. Since four billion years is almost half the anticipated life-time of our sun, life on other planets orbiting short-lived suns may not have had sufficient time to evolve into complex forms. This is because levels of oxygen will not have had time to develop sufficiently to support complex life, before the sun dies. Professor Catling said: "This is a major limiting factor for the evolution of life on otherwise potentially habitable planets." The research is published in the June 2005 issue of Astrobiology. ... Professor Catling is one of the country's first Professors of Astrobiology and has recently returned from the USA to take up a post at the University of Bristol. ... Professor Catling is an internationally recognised researcher in planetary sciences and atmospheric evolution. As well as his research into the surface and climate of Mars, Professor Catling aims to produce a more quantitative understanding of how the Earth's atmosphere originated and evolved. He comments: "Earth's surface is stunningly different from that of its apparently lifeless neighbours, Venus and Mars. But when our planet first formed its surface must also have been devoid of life. How the complex world around us developed from lifeless beginnings is a great challenge that involves many scientific disciplines such as geology, atmospheric science, and biology". ..." ("Few Planets Will Have Time to Form Complex Life," Universe Today, JunE 20, 2005)."Oxygen Helped Mammals Grow, Study Finds," ABC News/AP, September 29, 2005 ... Mammals, once tiny creatures scampering on the forest floor, grew larger as the amount of oxygen in the air increased over millions of years, a new study says. Today mammals, ranging from dogs and cats to elephants, dolphins and people, dominate the planet. It's a success story Paul G. Falkowski of Rutgers University and colleagues say was helped by the more than doubling of oxygen in the air over the last 205 million years. Their findings are published in Friday's issue of the journal Science. [Falkowski P.G., et al., "The Rise of Oxygen over the Past 205 Million Years and the Evolution of Large Placental Mammals," Science, Vol 309, 30 September 2005, pp.2202-2204. ] The researchers measured samples of material deposited on the seafloor going back millions of years. By measuring the amount of carbon-13 in the samples they were able to estimate the amount of oxygen in the atmosphere at a particular time. They found that the air contained only about 10 percent oxygen at the time of the dinosaurs. By 50 million years ago the oxygen level had risen to 17 percent and it was 23 percent 40 million years ago, they reported. Currently the air contains about 21 percent oxygen. The rise of oxygen "almost certainly contributed to evolution of large animals," the researchers reported. The oxygen needs of mammals and birds are three to six times as high as reptiles. The impact of an asteroid or meteorite about 65 million years ago is thought to have contributed to the demise of the dinosaurs. Their elimination also created an opportunity for the rise of mammals. There was an increase in small and medium- sized mammals in the first few million years after the end of the dinosaurs, the researchers reported. A second surge, from medium to large sizes, was seen between 50 million and 40 million years ago, they reported. ... [Also at CNN & Livescience: Another fine-tuned parameter without which we would not be here!] [ [top]7. Biogeochemical cycles 1. Hydrological (water) cycle 2. Carbon dioxide-silicate (rock) cycle The CO2-silicate cycle acts as a thermostat keeping the Earth's temperature within limits suitable for complex life (Ward & Brownlee, 2000, pp.18-19, 210-212). This negative-feedback cycle has enabled the Earth for billions of years, recover from extremes of global warming caused by increases in greenhouse gases methane (CH4) and carbon dioxide (CO2) (Cohen, et al., 2004). [top] 3. Carbon cycle 4. Oxygen cycle 5. Nitrogen cycle 6. Phosphorous cycle 7. Sulphur cycle 8. Calcium cycle 9. Sodium cycle 8. Life not extinguished in ~4 billion years The universe is like "A parking lot ... filled with cars, all in rapid, frantic motion. Their drivers ... acting without the slightest regard for safety, turning the steering wheels this way and that, stepping on the gas and slamming on the brakes, and all completely at random. Not only that, but every last one of them is blindfolded. ... The peaceful scene about me is subject to the most deadly danger" (Greenstein, 1988, p.17). "The longer one waits, the greater the chance of collision, and if one had occurred at any point in the past nothing of what I see would have come into being" (Greenstein, 1988, pp.17-18). "Had the Sun collided with a passing star in the epoch of the ancient Sumerians, none of us would have been born. The same would be true had the cataclysm occurred in the time of the dinosaurs. Our existence depends not simply on the avoidance of disaster this year or next, but throughout all of previous history" (Greenstein, 1988, p.18) "Our existence depends not simply on the avoidance of disaster this year or next, but throughout all of previous history" (Greenstein, 1988, p.18). "In cosmic terms our existence on this planet has been exceedingly brief ... and if a passing star had struck the Sun at any point in the preceding immense interval of time, humanity would never have come into being" (Greenstein, 1988, p.18). "The passing star need not have actually struck the Sun ... a near miss it could have dragged the Earth after it by its gravitational pull, detached us from orbit, and slung us off into the deadly cold of interstellar space ... In a matter of months every living thing would have frozen to death" (Greenstein, 1988, p.18). "An even more distant passage would have left us in our orbit but would have distorted the orbit's form into an ellipse: As the Earth alternately approached and receded from the Sun it would have been alternately too hot and too cold to support life" (Greenstein, 1988, p.18). "And finally, surrounding the solar system but at great distances from it is a vast cloud of comets, hundreds of billions of them. Even a far-distant passage of a wandering star would have been sufficient to deflect vast numbers of them toward us. The inner portions of the solar system would have become flooded with comets ... Had one of them struck our planet the energy released would have matched that of 100 million hydrogen bombs all going off at once, and great quantities of methane and ammonia, contained in comets, would have poisoned the air. Furthermore, the impinging comet would merely have been the first among many, and a world subject to such hammer-blows at a steady rate would have been uninhabitable, a wasteland" (Greenstein, 1988, pp.18,20). "In some way these disasters have not come to pass. ... They have not come to pass because there is an element in the actual situation not covered in the analogy of cars speeding about a parking lot. This element is that parking lots are small but space is big. The stars are exceedingly far away, and as a consequence collisions with them are rare. ... Rare enough to keep us safe. The remarkable thing about the arrangement of stars in space is the sparseness of their distribution" (Greenstein, 1988, p.20). "A strange way to construct the universe. It appears to have been designed by an extravagant, spendthrift hand. All that wasted space! On the other hand, in this very waste lies our safety. It is a precondition for our existence. Most remarkable of all is that the overall emptiness of the cosmos seems to lave no other consequence in the astronomical realm. Had the stars been somewhat closer, astrophysics would not have been so very different. ... About the only difference would have been the view of the nighttime sky from the grass on which I lie, which would have been yet richer with stars. And oh, yes-one more small change: There would have been no me to do the viewing" (Greenstein, 1988, p.20). ... Collision with a passing star is only the tip of an iceberg. Our existence, and that of every other life form in the universe, depends on a concatenation of circumstances, a network of interlocking conditions, each one of which must have held true in order for life to have come into being. The potential dangers that threaten us are so vast as to affect not just one person's existence, but that of life as a whole; and they arise not from circumstances such as war, pestilence, or famine, but from the very structure of the universe, from the nature of the laws of physics" (Greenstein, 1988, p.21). ... "none of those dangers have come to pass. But why have they not come to pass? The more one ponders this question the more mysterious it becomes. ... we are faced with a mystery-a great and profound mystery, and one of immense significance: the mystery of the habitability of the cosmos, of the fitness of the environment" (Greenstein, 1988, p.21)."And within the smaller, but still tolerably ample, compass of our planetary home, I would nominate as most worthy of pure awe-a metaphorical miracle, if you will-an aspect of life that most people have never considered, but that strikes me as equal in majesty to our most spiritual projections of infinity and eternity, while falling entirely within the domain of our conceptual understanding and empirical grasp: the continuity of etz chayim, the tree of earthly life, for at least 3.5 billion years, without a single microsecond of disruption. Consider the improbability of such continuity in conventional terms of ordinary probability: Take any phenomenon that begins with a positive value at its inception 3.5 billion years ago, and let the process regulating its existence proceed through time. A line marked zero runs along below the current value. The probability of the phenomenon's descent to zero may be almost incalculably low, but throw the dice of the relevant process billions of times, and the phenomenon just has to hit the zero line eventually. For most processes, the prospect of such an improbable crossing bodes no permanent ill, because an unlikely crash (a year, for example, when a healthy Mark McGwire hits no home runs at all) will quickly be reversed, and ordinary residence well above the zero line reestablished. But life represents a different kind of ultimately fragile system, utterly dependent upon unbroken continuity. For life, the zero line designates a permanent end, not a temporary embarrassment. If life ever touched that line, for one fleeting moment at: any time during 3.5 billion years of sustained history, neither we nor a million species of beetles would grace this planet today. The merest momentary brush with voracious zero dooms all that might have been, forever after. When we consider the magnitude and complexity of the circumstances required to sustain this continuity for so long, and without exception or forgiveness in each of so many components-well, I may be a rationalist at heart, but if anything in the natural world merits a designation as "awesome," I nominate the continuity of the tree of life for 3.5 billion years. The earth experienced several ice ages, but never froze completely, not for a single day. Life fluctuated through episodes of global extinction, but never crossed the zero line, not for one millisecond. DNA has been working all this time, without an hour of vacation or even a moment of pause to remember the extinct brethren of a billion dead branches shed from an evergrowing tree of life. When Protagoras, speaking inclusively despite the standard translation, defined "man" as "the measure of all things," he captured the ambiguity of our feelings and intellect in his implied contrast of diametrically opposite interpretations: the expansion of humanism versus the parochiality of limitation. Eternity and infinity lie too far from the unavoidable standard of our own bodies to secure our comprehension; but life's continuity stands right at the outer border of ultimate fascination: just close enough for intelligibility by the measure of our bodily size and earthly time, but sufficiently far away to inspire maximal awe." (Gould S.J., "I Have Landed," in "I Have Landed: Splashes and Reflections in Natural History," [2002], Vintage: London, 2003, pp.14-15)Gamma ray bursts are the most powerful explosions known A huge cosmic explosion could have caused a mass extinction on Earth 450 million years ago, according to an analysis by scientists in the US. A gamma ray burst could have caused the Ordovician extinction, killing 60% of marine invertebrates at a time when life was largely confined to the sea. These cosmic blasts are the most powerful explosions in the Universe. The scientists think a 10-second burst near Earth could deplete up to half of the planet's ozone layer. ... With the ozone layer devastated, the Sun's ultraviolet radiation could have killed off much of the life on land and near the surface of oceans and lakes. Gamma ray bursts are rare occurrences, but scientists estimate that at least one must have occurred near the Earth in the past one billion years. Scientists think that gamma-ray bursts are generated in two principal scenarios. In one scenario, a star collapses in on itself, giving birth to a black hole and releasing a high-energy jet of material travelling at close to the speed of light. The bursts could also be generated when two neutron stars collide. "A gamma ray burst originating within 6,000 light-years from Earth would have a devastating effect on life," said co-author Dr Adrian Melott ..."We don't know exactly when one came, but we're rather sure it did come - and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage." ("Ray burst is extinction suspect," BBC, 11 April, 2005) [top]
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Created: 3 November, 2003. Updated: 22 February, 2006.