The Moon: Earth's Sneezeguard 36
Mandi Walls writes "SF Gate is running an article about looking on the moon for pieces of Earth that may have been knocked into space by collisions with asteroids, etc. The article claims the guys responsible for the idea came up with it while stuck in traffic. They were probably digging for change for a toll in the seats."
Re:Would that make space a.... (Score:1)
Re:Would that make space a.... (Score:2)
Why go to the moon (Score:1, Funny)
Re:Why go to the moon (Score:1)
But, if you wait for the earth rocks on the moon to make the return trip on their own, you have a big problem with atmospheric burn-up. Don't forget that returning rocks will be hard to distinguish from the local variety that never made the trip.
I would rather go to the moon to start building a colony. Just think of the amusement rides alone.
Isn't the moon itself a piece of the earth? (Score:4, Informative)
In fact, after a little searching I found this [nasa.gov] at NASA:
A few more links: Perty image and more detailed explanation [nasa.gov]; a google search [google.com] on the topic.
Re:Isn't the moon itself a piece of the earth? (Score:2)
Re:Isn't the moon itself a piece of the earth? (Score:1)
Re:Isn't the moon itself a piece of the earth? (Score:2)
NASA's right (Score:1)
2) the Earth's rotation is slowing.
These phenomena are connected. The speed of the Moon orbiting around the Earth is increasing as the Earth's angular momentum is transferred to the Moon's orbital kinetic energy.
What's happening is the Earth-Moon system is connected by gravitational force which distorts the shape of the oceans from being roughly spherical into being a bulge pointed towards the Moon. The Earth rotates faster than the Moon orbits around the Earth. This means the tidal bulge is always being pulled forwards because of the frictional forces between oceans and Earth. This slight shift in the bulge slightly alters the overall gravitational field of the Earth thus pulling on the Moon and weakly accelerating it in its orbit to higher speed and causing it to drift slowly away from Earth at about 4cm/year. This is also explained well here [don-lindsay-archive.org].
Will
Re:Isn't the moon itself a piece of the earth? (Score:1)
If the moon is receding, something is pulling it away; you can't "back calculate" that because it would be some kind of idiosyncratic effect. By default, the moon would simply spiral into the earth.
Well, if you consider that the Earth/Moon system is not the only gravity well in the solar system, you might come to the conclusion that the Sun and/or Jupiter and/or any other massive object might have a cumulative pulling effect. Because the orbits and masses of these objects is known, it would be relatively easy to calculate this effect.
Tidal drag. (Score:2)
Well, if you consider that the Earth/Moon system is not the only gravity well in the solar system, you might come to the conclusion that the Sun and/or Jupiter and/or any other massive object might have a cumulative pulling effect. Because the orbits and masses of these objects is known, it would be relatively easy to calculate this effect.
To address two different points in these messages:
- Why would the moon "spiral into the earth" by default? There's nothing moving it in either direction in an ideal system.
- The moon recedes from Earth because of "tidal drag". The moon and the earth each deform each others' surfaces (creating the tides that we know so well, among other things). The net effect of this is that if one or both of the bodies are spinning, you get angular momentum transferred. The earth's rotation slows down, and the angular momentum the earth loses goes into the moon's tangential motion about the earth, which pushes it into a higher orbit.
This is what caused the moon to be tidally locked to us in the first place (i.e. always showing the same face to us).
We can calculate the rate of momentum transfer, but I don't have the numbers for that off the top of my head.
Exactly (Score:2)
Firstly, it is rather sad that such a basic yet interesting fact as this angular momentum transfer seems to be completely missing from the standard education curriculum.
Secondly, I've been trying to get to first base in compiling some data on the energy storage and rate of use in major planet-wide systems (down to, say, the gravitational potential of elevated water and ice stores) but am stuggling to find clear data.
Even in such an obvious area as total solar radiation the ratio between what the Sun is claimed to radiate (386 billion billion megawatts [seds.org]) and what the Earth is claimed to receive (4.4 x 1016 watts [nasa.gov]) seems to fly in the face of simple geometry which seems to me should have the earth intercepting one part in 1.1 billion of the Sun's radiation.
Digging for data on other energy systems, there is a total mess of approaches and even units used by different specialties that are going to make even a basic comparison table hard work to draw together, unless of course I am willing to become a "Creation Scientist".
Energy sources. (Score:2)
The number I keep hearing for solar energy flux is between 1 and 1.5 kW/m^2 at the Earth's distance from the sun, which gives between 1.5e17 and 2e17 watts for the whole earth. The amount that reaches the surface is less, and the amount that could be captured by any practical harnessing scheme would be much less, but I digress. This is roughly in line with the NASA numbers.
At this flux, total solar energy output is between 3e23 and 4e23 watts. SEDS claims 4e26, so they probably switched "million" and "billion" somewhere.
Digging for data on other energy systems, there is a total mess of approaches and even units used by different specialties that are going to make even a basic comparison table hard work to draw together
What gets me is conversion to/from ergs with old articles
My suspicion is that solar power flux dwarfs most of the mechanical potential energy stored on Earth's surface features. Earth's angular momentum holds one heck of a lot of energy, though, as does that of the earth-moon system, so tidal will work for quite a while.
Wind is recycled solar. Ditto anything involving growing crops.
Energy stored in wind at a given time can be estimated by assuming an average velocity (maybe look up the speed of the trade winds). Mass of the atmosphere is easy to calculate (about 10 tonnes per square metre of the earth's surface; it's just the atmospheric pressure).
I have no idea how much energy is stored in hydrocarbon reserves. You can probably get an upper limit by looking at the elemental abundance of carbon in the earth's crust, and assuming that the upper km is accessible.
The other big source is geothermal, which is driven by radioactive decay in the earth's core. I'm afraid I don't have numbers for the energy flux offhand, but it should be straightforward to calculate. Anything that's still fissioning now will have a long enough half-life to last for billions of years more.
Fissionables on the earth's surface will be dwarfed by geothermal, which effectively makes all radioactives on the planet available for harvesting (albeit over quite a long time).
Good luck with your search, in any event
Re:Isn't the moon itself a piece of the earth? (Score:2)
Re:Isn't the moon itself a piece of the earth? (Score:3, Interesting)
"As magmas move through the crust towards the surface or as lava flows over the Earth's surface, they may pickup chunks of surrounding rocks. Sometimes, the magmas and lavas are not hot enough to melt the captured rocks. Once the molten rock solidifies, the plucked rocks remain trapped in the igneous matrix. These trapped rocks are called xenoliths. If the trapped materials are individual minerals, they are called xenocrysts.
Xenoliths, zoned phenocrysts, and xenocrysts (like metamorphic and weathering features) are often easily identified under the microscope and sometimes even in the field. In some cases, a geologist may be interested in dating xenoliths, zoned phenocrysts, or the xenocrysts. However, obviously, if the geologist is interested in dating the younger matrix, he/she will look for and avoid any xenoliths, zoned phenocrysts or xenocrysts. While mainstream geologists know how to avoid xenoliths, zoned phenocrysts, and xenocrysts when dating igneous rocks, creationist Steve Austin apparently was not careful to avoid them when he conducted his "research" at Mt. St. Helens or the Grand Canyon, see " A Criticism of the ICR's Grand Canyon Dating Project by Chris Stassen and compare with Excess Argon within Mineral Concentrates from the New Dacite Lava Dome at Mt. St. Helens Volcano, by Steven Austin. In his Mt. St. Helen's study, Austin collected what he thought was a freshly solidified dacite. He removed the gabbro xenoliths, but there's no mention if he found and removed any lighter colored, less obvious xenoliths, such as andesites or quartz diorites. Austin states that xenoliths of gabbro, quartz diorite, basalt, and andesite are common at the Mt. St. Helen site."
The study [icr.org] by Austin the author, a Dr. Henke, is referring to is one which claims impossibly old dates for fresh dacite.
We could go on for a long time, but I would simply say that science is self-correcting: it is a field which encourages criticism and revision, so long as the criticism is valid and demonstrable. No good scientist would ever claim to any perfection in his or her work. A scientific theory is only valid so long as it has been demonstrated in experiment and has not been disproven by other experiments. The reason why I have such a hard time accepting what you're saying is because, so far as I can tell, it has not stood up to peer review.
Re:Isn't the moon itself a piece of the earth? (Score:2)
More generally, we could go on for days like this on any topic. Errors in data will always come out. You can never completely get rid of human error. If you want to convince me that radiometric dating is pseudoscience, you'll have to give some idea as to what, other than human error in measurement, would cause such skewed results. There are several areas with potential for inaccuracy: the methodology, incorrect assumptions about the properties of various radioactive elements used in measurement; errors in the underlying theory of radioactive decay. But simply giving specific examples where dating has been shown to be inplausable with no context for the scope of the studies nor the larger context of the field (with numbers for accurate/inaccurate results on objects with known time periods). There must be a reason for the inaccuracies; by themselves, as exceptions to the rule, they prove only that radiometric methods have been inaccurate in the past. They do not prove that radiometric methods have always been inaccurate, nor do they prove that radiometric methods will be inaccurate.
Re:Isn't the moon itself a piece of the earth? (Score:1)
It is possible the basalt was a product of mixing magmas of two different isotopic compositions. Basically on an isochron diagram (slope of which is the date of the rock), the line for initial crystallization is a flat line, the slope of which increases throughout time. However if mixing is occurring, the initial line will have a positive slope to begin with, yet the slope still increases the same rate throughout time. The result of this is a bogus age that is much older than the crystallization of the magma. A good example of this is some basalts from the East African Rift Valley.
Re:Isn't the moon itself a piece of the earth? (Score:1)
Another thing you can do to reduce error in dating is careful sample preparation. For example, U-Pb dating using zircons from granite can be made more accurrate not only be separating out the zircons from the host rock using a good process, but by grinding away the outer, possibly altered layers of the crystal before analysis.
Re:Isn't the moon itself a piece of the earth? (Score:2, Informative)
The other interesting thing is that the same date is found +- a couple millions years or so using different isotopic systems, which is a great check for accuracy.
strange places for cool ideas (Score:1, Interesting)
examples: Newton determined that buyuncy (sp?) exists because he felt lighter in weight after getting into the bathtub one morning. This helped him solve a problem given to him by the King who said his new crown felt lighter than the previous. The story goes that Newton ran through the streets nude shouting "Eureka!! Eureka!!" His discovery helped him determine that the crown was not 100% gold, but rather some other metal with a layer of gold on the exterior. This was determined before he tore the crown open to confirm his theory.
example 2: The guys who found a key exchange algorithm for quantum encyption keys. They had a chance meeting with each other at a train station after one of their trains ran late. Standing on the platform, they had, as Simon Singh put it in his book The Code Book, "one of those eureka moments" where they figured out the trick needed.
Archimedes, not Newton (Score:3, Informative)
Re:Archimedes, not Newton (Score:1, Insightful)
I don't think that Archimedes's discovery was that a submerged object will displace its volume in water (that's pretty obvious), but rather that a *floating* object would displace a volume of water of the *same weight* as the floating object (a much deeper result).
Re:Archimedes, not Newton (Score:2)
That's volume displacement for submerged objects.
I thought Eureka was... (Score:1)
Re:strange places for cool ideas (Score:1)
Re:strange places for cool ideas (Score:1)