Posted on 03/20/2004 7:38:37 PM PST by Leroy S. Mort
Without the Moon, there would have been no life on Earth.
Four billion years ago, when life began, the Moon orbited much closer to us than it does now, causing massive tides to ebb and flow every few hours. These tides caused dramatic fluctuations in salinity around coastlines which could have driven the evolution of early DNA-like biomolecules.
This hypothesis, which is the work of Richard Lathe, a molecular biologist at Pieta Research in Edinburgh, UK, also suggests that life could not have begun on Mars.
According to one theory for the origin of life, self-replicating molecules such as DNA or RNA emerged when small precursor molecules in the primordial "soup" polymerised into long strands. These strands served as templates for more precursor molecules to attach along the templates, creating double-stranded polymers similar to DNA.
But the whole theory fails without some way of breaking apart the double strands to keep the process going, says Lathe. It would take some external force to dissociate the two strands, he says.
Doubling up
As an analogy, he points to PCR, the technique used to amplify DNA in the lab. DNA is cycled between two temperatures in the presence of appropriate enzymes.
At the lower temperature of about 50 ýC, single DNA strands act as templates for synthesising complementary strands. At the higher temperature of about 100 ýC, the double strands break apart, doubling the number of molecules. Lower the temperature, and the synthesis starts again. Using this process, a single DNA molecule can be converted into a trillion identical copies in just 40 cycles.
Lathe believes that thanks to the Moon, something similar happened during Earth's early years. Most researchers agree that the Moon formed five billion years ago from debris blasted off Earth in a giant impact.
A billion years later when life is thought to have arisen, the Moon was still much closer to us than it is now. That, plus the Earth's much more rapid rotation, led to tidal cycles every two to six hours, with tides extending several hundred kilometres inland, says Lathe. Coastal areas therefore saw dramatic cyclical changes in salinity, and Lathe believes this led to repeated association and dissociation of double-stranded molecules similar to DNA.
When the massive tides rolled in, the salt concentration was very low. Double-stranded DNA breaks apart under such conditions because electrically charged phosphate groups on each strand repel each other.
But when the tides went out, precursor molecules and precipitated salt would have been present in high concentrations. This would have encouraged double-stranded molecules to form, since high salt concentrations neutralise DNA's phosphate charges, allowing strands to stick together.
Unrelenting cycles
These unrelenting saline cycles would have amplified molecules such as DNA in a process similar to PCR, says Lathe. "The tidal force is absolutely important, because it provides the energy for association and dissociation [of polymers]."
Many researchers do not believe DNA and RNA were the first replicating molecules. Graham Cairns-Smith of the University of Glasgow, UK, thinks much simpler "genetic" material formed first, from the crystallisation of clay minerals.
But he says Lathe's idea deserves attention. "Whatever the replicating entities were that started the evolutionary process, it would be significant that they lived in an environment in which the conditions were changing."
If the theory is right, life could not have evolved on Mars, says Lathe. Phobos, the larger of Mars's two Moons, is so small that the tidal forces it generates are just one per cent of those generated by our Moon. "Even if there was water on Mars, life could not have evolved there because these polymers could not have replicated," he says.
could
what speculative drivel. Does someone get paid to write this nonsense?
Yeah, who do these people think they are coming up with hypotheses - scientists?
And what makes these so-called scientists think they can get away with making anything less than categorical assertions of god-like certainty? Anything less than WWF-like bravado is the same as total capitulation to all alternate theories. Science has NEVER made progress by making tentative, qualified statements.
From here:
http://www.astronomy.com/Content/Dynamic/Articles/000/000/001/611spati.asp
"While Earths axial tilt has only varied between 22 to 24.5 degrees in the past 10 million years, Mars has experienced a more extreme wobble, ranging from 14 to 48 degrees."
Another interesting read:
http://www.rps.psu.edu/jan97/planets.html
"The obliquity of a planet is the angle of its spin axis -- that imaginary rod that skewers a planet through the poles -- in relation to the plane of its orbit. In Earth's case, this angle is a modest -- and reasonably steady -- 23.5 degrees, enough of a tilt to account for our seasons. Because of Earth's obliquity, in the northern hemisphere the winter sun stays low in the sky, casting its rays obliquely across the landscape. In summer it climbs to more nearly overhead, an angle much better for warming."
---snip---
"Mars, Laskar showed, still does, its obliquity varying chaotically between 0 and 60 [Note: I did notice there was a difference in the numbers] degrees. The only thing that saved Earth from a fate worse than Mars', he says, was hooking up with the moon.
A little orbital mechanics may be in order here. Earth is a body in complex motion. It rotates, of course, once every 24 hours. At the same time, on a different time scale, it revolves around the sun. But there are other, subtler, motions which must also be accounted for. Earth's imperfection as a sphere, for one thing, adds a motion called precession, akin to the wobbling of a spinning top. Earth wobbles, as noted above, only slightly and in very slow motion, its obliquity oscillating from 22 to 24 degrees every 40,000 years.
Meanwhile, however, the gravitational pull of the other planets in the solar system, especially the giants Jupiter and Saturn, causes a different kind of precession: a wobble in the plane of Earth's orbit. Imagine the orbital plane as a solid object, a spinning frisbee or a dinner plate, with the sun a dollop of mashed potatoes in its center, and Earth a wad of chewing gum stuck to its outer rim. The insistent tug of these outer, larger planets against the sun's stronger pull causes the plate to wobble as it spins.
The real action, in terms of shifting obliquity, comes when these two types of wobble -- the planetary and the planar -- stumble onto the same frequency. Then you get what's known as a spin-orbit resonance: in synch, the two motions combine their energy, creating a much larger force. It's not unlike the kind of timing it takes to keep a hula-hoop spinning around your hips, or to successfully push a child's swing. For a planet, however, resonance means chaos, as two small competing wobbles become one huge concerted one.
What saves Earth from falling into a spin-orbit resonance, Laskar says, is the moon. Because of its size and proximity, the moon exerts a strong gravitational pull of its own on our home planet -- a pull which turns out to be a stabilizing influence. The lunar effect acts to accelerate Earth's global precession, maintaining it at a steady frequency well higher than the torpid wobbling of the orbital plane. Take the moon away, Laskar says, and keep things otherwise the same -- give Earth the same mass, orbital position, rotation rate, etc. -- and Earth's obliquity would fluctuate between 0 and 85 degrees."
and it would mean a much lower value of the Drake Equation variables Ne and Fl: a lower probability of extraterrestrial life.
That I am not sure of. Life may be just as likely, but adapted to those environments. I just dont know. Life sure seems to be able to live in the extremes on this planet.
More later - I am just passing though at the moment
BWAAAHAHAHAHAHAHAHAHAHAH!
Yep. No place for the Justice League's Watchtower to keep us all safe.
Hey, that's close enough to "abiogenesis of primitive autocatalysis has been disproven completely, end of story" for creationist work.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.