Periodic mass extinctions appear to have happened at least several times throughout Earth's history. In some cases most of the life forms which existed just prior to these extinctions were completely wiped out. The K/T boundary marks the end of the reign of the dinosaurs and is on the order of 65 Million years old. It is popularly believed that a large asteroid struck the Earth causing a world-wide change in climate which interrupted the food chain. No veggies means no veggie eating dinosaurs and then no dinosaur eating dinosaurs. The extinction of the dinosaurs allowed mammals to evolve and if they had not died out we probably wouldn't be here to talk about it. Recently
discovered evidence points to a mass extinction which
occured between 248 and 251 Million years ago when
another large asteroid may have struck the earth.
Since it is difficult to find a terrestrial based cause for these extinctions which repeat at regular intervals over such a long time scale, it seems reasonable to assume that something happens every 62 MY (or so) which puts us in harms way. In it's orbit around the center of the Milky Way Galaxy, our Solar system may follow a sinusoidal motion from the top to the bottom to the top (and so on) within the Orion arm which we go around in. If the period of one complete cycle through the arm is around 124 M years, we would pass through the middle of the ring (the most dense part) twice every 62 M (or so) years. As we spin around in the arm our forward motion (~150,000 miles/sec) is continuous, but if we go up and down also, the Earth's motional speed would change with position due to angular motion. There is also the possibility that we move side to side within the arm but, for the sake of this discussion, we will ignore that for now. We would traverse this much more dense part of the ring at maximum velocity, much faster (in the vertical axis) than when we reach the outer edges of the arm where that relative motion (vertically) stops altogether so that it can reverse direction. If we didn't stop moving (in the vertical axis), we would just fly off into deep space but the mass concentrated nearer the center of the arm provides gravitational force with acts to pull us back in for yet another cycle. It may be that large asteroids do not 'hit us', but rather we run into them. Also, traveling at that much greater rate of speed means that we have a better chance of hitting objects because we are 'sweeping' through a larger sectional area of space per unit of time. The center of the ring isn't a hard boundary, it is just more dense and there is a density gradient as you move away from the center. So, there is some latitude for interval timing due to this 'kill zone' principal. Also, since not everything in the ring rotates at the same speed, conditions through the next pass may not be the same as the last one, so hitting something (or not) becomes a bit of a crap shoot. On some passes Earth may get lucky and pass through the middle of the ring unscathed - which would explain gaps in the mass extinction record.
The graphic below which illustrates my theory.
If the last mass extinction was 65 MY ago and the half cycle period is around 62 MY then we should be about 20 Light Years away from the centerline of the Orion arm and moving away from the centerline. But, we may not be out of the woods ... or rocks ... yet. If my calculations are right and the dinosaurs were wiped out by a big asteroid 65 MY ago then we were due for the next one 3 Million years ago. In other words, either we are ~3 Million years over due or we got lucky on this pass. Lets look at a few numbers. The Milky Way Galaxy is about 100,000 Light Years in diameter. Our Solar system is about 2/3 of the way out from the galactic center and we revolve at 250 kilometers or about 150,000 miles per second. We make one revolution every 226 MY which means that we have made about 20 revolutions since the Earth was formed about 4.5 BY ago. With a cycle period of 128 MY, our solar system would have completed 35 sinusoidal cycles or 70 centerline crossings. If space was much dirtier previously than it is now, impacts would have been more probable and may have prevented life on Earth from forming sooner. It is estimated that there are between 200 and 400 Billion other stars in the Milky Way and that at least some of those have planets. It is likely from looking at our own Solar system that at least some of those planets probably have moons. Not to mention rogue asteroids, comets and planet X's, that is a lot of stuff and until asteroids or comets are near a luminous source (like our Sun) they are very dark. Most big telescopes are funded to do specific tasks, they don't hunt for these civilization killers, and the number of amature astronomers world-wide who look for these objects is probably less than the staff at your local MacDonalds.
On June
15, asteroid 2002 MN came within 120,000 km of the Earth
(7 times closer than the moon). On March 2nd 2009, Asteroid DD45 missed Earth by 75,000 KM. In 2029 asteroid 99942 Apophis will come so close to Earth that it will be the closest object to Earth in human history. Scientists are not sure yet whether Apophis will hit the Earth in 2036.
When the big one comes, it is likely that the only notice you will receive (if you are awake and looking in that direction) will be the thousand foot high wall of debris (which was formerly your neighborhood) coming at you at about mach three when one of them strikes the Earth. If you think there is anything we could do to stop one of these killer asteroids if one were discovered tommorrow, you have been watching too many hollywood movies. NO ONE has a plan on how to deal with this (although there are plenty of ideas) especially our government which, more realistically, would probably spend our last days in typical fashion trying to decide who should pay for such a project.
Sweet
dreams.
Why wobble ? Why not ? Do other bodies/systems in the ring wobble ? It seems likely that at least some would. If this is the case their cycle rate would be dictated by their respective masses and proximity to other objects. Plotting their paths would be akin to the old spirograph plots since it is unlikely that they would all have the same frequency, amplitude or phase - or that those would remain the same. Approaching the ring we are accelerated by the mass in the rings and leaving it we are decelerated by it affecting the rate and therefore perhaps the periodicity of the cycle if the ring mass differs to any degree on each pass which also seems likely. If all gravitational bodies act mutually on each other then our passing through the ring must have an effect (even if slight) on all of the other mass there, possibly causing perturabations which must be something like chaos theory. What would have set the cycling action in motion ? A tug from another Galaxy eons ago ? Due to their varying masses different bodies/systems would have been affected unequally and once set in motion and with gravitational slingshotting to keep it in motion and no appreciable friction to slow it down would it continue forever ? Would the rings tend to 'smear' after a while or would gravity or some other force keep them contained ?
Feeling a little confused ? Can't tell if you are coming or going ? I have discerned at least
five degrees of motion affecting a person standing still
on the Earth relative to a distant point in space and
here is how they relate: 1) The Earth rotates on its axis. Relative to a fixed point in space this motion could be positive, negative or zero depending on the persons position on Earth during a 24 (+/-) hour period. Inclination of Earth's axis (22.5 degrees) is a slight factor. Also, the Earth's rotation rate is slowing ever so slightly through friction with the atmosphere and the core which both spin slower than the Earths crust. 2) The Earth revolves around the Sun. Again this motion could be positive, negative or zero and variable depending on the position in its orbit during the 365.2564 days it takes the Earth to make one complete orbit. Rate is slowing slightly through friction with solar wind, mass acquisition and possibly through bombardment from opposing vectors (all very slight effects). 3) IF the Solar system does the cyclic maneuver mentioned above, that motion could be positive, negative or zero and variable through a cycle and rotational change in galactic orbit. Rate through one cycle changes dramatically depending on position, but the cyclic rate is probably about the same unless the rings' mass changes or the Solar system mass changes or the Solar system is affected by another massive object (i.e. collision or gravitational). 4) The Solar system revolves around the center of the Milky Way. Again, positive, negative or zero and variable depending on its' position in the galactic orbit. This rate is slowing slightly through friction, mass capture and possibly by mutual gravitational tugging, especially if larger objects rotate slower. A large over-all change in this motion is almost inconceivable due to the enormous mass of the galaxy. 5) The Milky Way is moving away from its origin in the Big Bang. This motion would always be positive or negative and does not change unless the universe ceases to expand and begins to contract (so called "cyclic universe" theory). The expansion rate of the universe should be diminishing slightly(*) due to mutual gravitational attraction between galaxies and friction (a much smaller effect). One exception to this rule would be supernova stars loosing mass to deep space, but if cold hydrogen exists in sufficient quantity, its capture could offset this effect. Very massive objects may likewise attract even more mass. Again the galactic mass is so enormous that changes in velocity are very slight unless it is acted upon by an even larger body, which is virtually inconceivable. Obviously all of these motions interact relative to each other and they all have differing vectors and rates and most change with time. Effects worth mentioning are: Gravitational pull exerted on any or all of the above by massive and/or very dense (though possibly very distant) objects such as other galaxies, black holes, neutron stars, things which may exist beyond the known boundaries, etc.. Impacts with large objects and the relative vector (angle) of these impacts. Mass capture (or loss) by the Earth, the Solar System or the Galaxy. Dark matter (cold hydrogen gas) which may cause friction or have a weak gravitational effect. And things I haven't thought of yet. * Update (2006) Just when you thought you had it all figured out... Recent studies indicate that the expansion of the universe is actually speeding up, possibly due to short-lived particles which actually attract us (and everything else) - go figure. I just knew the universe sucked.
See
also: www.lxrdesign.biz/THEEND.htm
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