Meteorites, Cosmic Dust, and Mass of Earth
There's a great story in the NY Times about a Norwegian jazz musician, who also happens to collect interstellar particles that have fallen to earth.
So, we're constantly being bombarded with 'micrometeorites'. Other material comes in via large meteors, like the one at Chelyabinsk in Feb 2013 (fortunately, not too many of them.) But according to the article in the NY Times, there is a constant rain of dust falling out of space. The article mentions 4,000 tons annually.
Now here's a question for the more scientifically literate among us. As gravity is proportional to mass, would this accretion of materials add up to enough additional mass to actually increase the force of gravity on earth? Consider that the heyday of dinosaurs was from around 230 - 200 mya. Since then, if there has been 4,000 tons of material falling every year, that amounts to 4000 x 200 million - which I'm sure is a pretty large amount of stuff - 800,000,000,000 tons, or 725,747,792,000,000 kg if my calculation is correct. Dr Google tells me the mass of the earth is 5.972 × 10^24 kg. So here my general knowledge of maths fails. Would an increase of that magnitude, have a measurable effect on the overall gravity of the earth?
(I ask this because it is well-known that some dinosaurs were huge by today's standards, so if the force of gravity were slightly less, that might go some way to explaining the difference.)
After decades of failures and misunderstandings, scientists have solved a cosmic riddle — what happens to the tons of dust particles that hit the Earth every day but seldom if ever get discovered in the places that humans know best, like buildings and parking lots, sidewalks and park benches.
The answer? Nothing. Look harder. The tiny flecks are everywhere.
So, we're constantly being bombarded with 'micrometeorites'. Other material comes in via large meteors, like the one at Chelyabinsk in Feb 2013 (fortunately, not too many of them.) But according to the article in the NY Times, there is a constant rain of dust falling out of space. The article mentions 4,000 tons annually.
Now here's a question for the more scientifically literate among us. As gravity is proportional to mass, would this accretion of materials add up to enough additional mass to actually increase the force of gravity on earth? Consider that the heyday of dinosaurs was from around 230 - 200 mya. Since then, if there has been 4,000 tons of material falling every year, that amounts to 4000 x 200 million - which I'm sure is a pretty large amount of stuff - 800,000,000,000 tons, or 725,747,792,000,000 kg if my calculation is correct. Dr Google tells me the mass of the earth is 5.972 × 10^24 kg. So here my general knowledge of maths fails. Would an increase of that magnitude, have a measurable effect on the overall gravity of the earth?
(I ask this because it is well-known that some dinosaurs were huge by today's standards, so if the force of gravity were slightly less, that might go some way to explaining the difference.)
Comments (48)
Quoting TimeLine
Why?
Because it is simple Newtonian physics.
What exactly is the reasoning behind your assumption that there would be any measurable effect on the overall gravity of the earth? Are you afraid that if earth' mass increased, the earth' orbit will decay or that it may even collapse out of orbit?
Poor shiny little sun of ours, so underestimated.
I saw the Mars film with Matt Damon recently, and a blooper that was pointed out that Mars' gravity is about 35% (I think it was) of Earth's - therefore the monumental dust storm that triggered the evacuation would have been nearly so powerful in reality, because the atmosphere is much thinner due to that factor.
So I think there's nothing wrong with the principle, but the numbers aren't going to work out. From what I can ascertain, the Earth's mass is 5,972,000,000,000,000,000,000,000 kg, and the total mass of interstellar stuff that would fall over 200m years @4000 tons per year, would be 725,747,792,000,000 kg. I haven't figured out how to calculate the percentage that the second figure is of the first, but at a glance I think it will be negligible.
Quoting TimeLine
No, as I said, I wondered if it might account for the fact that some terrestrial dinosaurs are much bigger - enormously bigger - than current terrestrial animals. A change in the Earth's gravitational field *might* account for that.
PS// I now think the total sum of meteorite accretion is around 8 billionths of the total mass, in which case it is neglible.
http://gizmodo.com/5882517/did-you-know-that-earth-is-getting-lighter-every-day
So their estimate is 10x the figure quoted in the article I referenced.
The upshot is, none of the figures are enough to affect gravity - but in principle, it would, if the amounts involved were of a much higher order of magnitude.
Quoting TimeLine
I was just interested. I figured, hey, maybe this is a factor that hasn't been considered. But I've already answered my own question - the amounts involved are negigible, it would seem, compared to the overall mass of earth. But then, the Earth itself is an accretion of such debris, so it might still be an open question.
Also another idea is that organic material might also turn up on comets and in interstellar dust, which actually alters, or contributes to, Earth's gene pool. This was the idea behind a book by astronomer Fred Hoyle, The Intelligent Universe. That is one example of the delightfully-named theory of 'panspermia'. (Think about the etymology of that word for a moment.)
A quick google search suggests that it is 40,000 and not 4,000.
Yeah, there are quite a lot of theories on the astrobiological origins of life, I mean, what was earth before our sun captured it? But, if you want to think of particularly mass-distribution effects, a more interesting subject would be earths' "wobble" - whether precession as it rotates around the axis or the violence of natural causes - that causes the earth to shake, including droughts, earthquakes and heavy rainfall. So the distribution of mass, basically, is affecting climate change particularly with polar melting, which is pulling the axis. Pretty spooky.
one candidate critter for an extra-terrestrial origin is the tardigrade (also known somewhat charmingly as the 'moss piglet'). It can survive in deep space and is quite unlike any other phyla (is that the word? Anyway if Scott Pruitt has his way they'll probably be the only things left alive in 100 years.)
The sun didn't "capture" earth, earth and the sun, plus all the other planets, moons, asteroids, comets, and various leftovers, all arose out of a disk of dust that happened to accumulate in this area of the Milky Whey and eventually went thermonuclear.
Quoting Wayfarer
What about creatures from the Jurassic and Cretaceous that were not spectacularly large?
According to the all-knowing wikipedia tardigrades can survive vacuum, radiation, high pressure, high temperatures, etc. for a while -- not indefinitely. Eventually radiation, heat, pressure, vacuum, and so forth causes serious damage. Still, they are very remarkable little creatures.
From the figures that you gave, the micrometeorites have, during the period you specify, increased the Earth's mass by about a tenth of a billionth of what it was at the start of that period.
That would increase gravity at the Earth's surface by about the same fraction.
Well, actually a little less, if you count the fact that we're standing just a little bit higher, on top of that newly-arrived material.
For a given constant uniform density of material, a planet's surface-gravity is proportional to the planet's mass, divided by the square of its radius.
For some given constant uniform density, that would make a planet's surface gravity proportional to its diameter, or to the cube-root of its mass.
Looking at it that way, then you could say that the Earth's gravity would have increased by only 1/30 of a billionth of its value at the beginning of that period.
Michael Ossipoff
As the material contracted gravitationally, it would have tended to form a roughly spherical shape, except that, as the rotating material contracted, conservation of angular-momentum would have caused a disk of material to be spun-out along the equator of the forming Sun. That's the ecliptic disk from which the planets were formed.
Michael Ossipoff
I did acknowledge that earlier in the thread. It remains mysterious, however, why the mega-fauna of that age was so much bigger than anything that exists today. Some of the brachiopods weighed as much as today's whales. I was wondering if there is any global change that might explain this disparity.
Precession of the equinoxes, a top-like wobble caused mostly by the gravitational pull of the Sun and Moon on the Earth's equatorial-bulge, affects our climate as follows:
Because the Earth's orbit isn't perfectly circular, but rather a bit elliptical, it has a minimum-distance from the Sun (Perihelion) and, opposite it, a maximum-distance (Aphelion).
As the Earth precesses, the equinoxes move around the ecliptic (plane of the Earth's orbit).
The equinoxes are the points on our orbit where our orbital plane (the ecliptic) crosses the plane of the Earth's equator. At those places on our orbit, day and night are of equal length.
Precession moves those points around the ecliptic. Of course then the solstice-points of our orbit (where the Sun reaches its maximum distance north or south of the celestial equator) also move around the ecliptic in the same way.
So then, there's a time when the summer solstice occurs right at the perihelion (close approach) of our orbit.That will be a particularly hot summer. Right now, our summer solstice occurs near the aphelion (greatest distance from the Sun). That means that our summer is particularly cool.
Michael Ossipoff
Yes, there are some very interesting facts concerning the earth. The equator is not stable, to begin with. The magnetic poles do not line up with the true poles, and are moving. And, the north/south axis flips from time to time, to mention a few, other than the wobble.
Likely, after the KT impact greatly reduced the food-supply and the temperature, those things tended to kill-off reptiles, because of their greater temperature-sensiivity (or near-reptiles, if that's what the dinosaurs were), and big animals that needed abundant food.
Eventually, of course, some time after mammals took over, some of them, too, became big. The Baluchitherium ("Beast of Baluchistan) was much bigger than any modern land animal.
Maybe the dinosaurs were so big because food was so abundant before the impact. Maybe, when the KT dust-cloud settled, climate was again providing an abundant food-supply, allowing those large mammals.
Maybe later, climate became less favorable, and hunting by humans made large animals more vulnerable. But I think animals the size of Baluchitherium were already gone before humans arrived on the scene, and the Mammoth and Mastedon were the biggest then. ...and were evidently hunted to extinction by humans.
So, my first guess would be that, for some reason, modern climate doesn't provide a food supply sufficient for animals as large as the Baluchitherium, and already didn't when humans appeared.
But I'm just guessing.
Michael Ossipoff
Precession, and also the rotation of the absides (perihelion and aphelion), caused by gravitational perturbations by the other planets--but mostly by Jupiter. Together those two things result in an effect that has a period of about 20,000 years.
Another cyclical change caused by planetary perturbation is changes in the Earth's orbital eccentricity.
Someone showed that these effects coincide well with ice-ages.
Of course with the arrival of the Anthropocene Epoch, we're the new main influence on climate.
Michael Ossipoff
It isn't so much a question of nutrition, as how the skeletal and muscular dynamics of creatures that large could hold together. Like, move too quickly and suffer a major muscle malfunction. There was talk at some stage that many of the long-necked dinosaurs spent most of their lives partially submerged so as to buoy them up. But those types of dinosaurs were again orders of magnitude larger than ancient mammals. The notion that gravity was different 250 million years ago is at least consistent with that, granted that there is no way to account for such a difference, and it is never really considered as an hypothesis.
Sure, larger animals are less able to support their weight on land. Maybe Brontosaurus ("Apatosaurus"), Diplodocus and Brachiosaurus spent most of their time in deep swamp-water, where bouyancy would help support their weight, and where they could be safe from land-predators.
Maybe a reduction in the amount of swampland prevented large mammals from having that opportunity.
Michael Ossipoff
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Jurassic-III is the best, because it's funny.
Jurassic II is next best, because of the priceless T-Rex on Main-Street. ...and the introduction of the 1.5 foot tall bipedal predator dinosaurs.
I didn't care for #4, but I liked its Pterodactyls.
Jurassic-1 suffered too much from Malcom's personality.
By the way, in #3, when the plane fell from the tree, if the fall took 3 seconds, then the 65 mph impact with the ground would be difficult to survive.
And did that little para-sail speedboat come all the way from Costa Rica, at least a 20 or 30 hour round-trip, across open ocean?
In #2, the ship-captain promised that if the team on the island radioed them, they'd be there in 2 hours. Why didn't they respond when called?
And of course the movies' main menacing dinosaurs, Tyrannosaurus Rex and Velociraptor were Cretaceous, not Jurassic.
Michael Ossipoff
And by what theory could gravity be different 250,000,000 years ago? Had Newton overlooked something?
Speaking of movies - that excellent sci-fi thriller with Matt Damon trapped alone on Mars - it was pointed out that you couldn't have a gale of the kind that disabled the station on Mars, because the atmosphere only has a third of the density of Earth's.
Less than 1/3, if I remember correctly. And the wind-pressure at a given windspeed is proportional to the air-density. So yes, the wind would be a lot less damaging.
Yes, it does seem a bit odd that everything, even the dragonflies, were bigger in those earlier eras.
I read that the Pterodactyls, especially the big Pteranadon, wouldn't have really been able to fly. They've suggested that Pternatadon, and maybe the other Pterodactyls, soared on a cliff-updraft to hunt fish, and then cllmbed back up to their nest, along the cliff-face.
And i've read that there was a Pterosaur even bigger than pteranadon.
Maybe that's it. The giant dragonflies were probably not bigger than some modern birds known to be able to fly.
Aerodynamicists used to say that a bumblebee couldn't fly, by their calculations, until someone figured out the various tricks that flying insects use. Like the "clap-fling" used also by pidgeons (rock-doves).
In Jurassic Park, of course the Pteranadons fly easily, but that might not be accurate. They fudge things when it suits the story. For example, I read that it's believed that the Pterosaurs were fish-eaters, but theyi're all chasing humans in Jurassic-III and jurassic-IV.
Michael Ossipoff
But the 170 mph sand-grains could still do erosion damage.
Michael Ossipoff
Yes. Yes there is.
:-|
Quoting Metaphysician Undercover
That's because of the earths core. The magnetic field - which is there to shield us from outside stuff and something visually seen in auroras - is constantly changing or reversing and geomagnetic excursions could occur at any stage; actually, the field itself is decreasing in shield strength.
Earth has anaemia.
Concerning gravity: Of the eight planets, five of them (including Earth) have pretty similar gravity, but the closest one to us is Saturn, despite massing over 100x as much. So additional mass alone does not necessarily translate to a weight difference. Mars and Mercury weight are almost identical at 3/8 Earth, and Jupiter is in a class by itself at 2.5x.
I did, and they don't appear to offer any. It's still not known.
We can't trace the long-term (over millions of years) increase of T Rex & Co.'s size. Then too, we don't have any DNA from T R & Co. Presumably they had genes which enabled them to get that big.
Look at dogs: they range from teacup miniatures to Great Danes and bigger. Only a few genes account for all of the dog differences. A horse that the Vikings used and spread around Europe ambles. It's walk is very smooth and even. Nice to ride. It has the odd habit of picking up it's front feet when it walks--like it was doing an exaggerated prance. 1 gene mutation granted this horse the ability to walk that way. Other horses can't do it.
Maybe T R & C had the good fortune to start out relatively large, bigger than whatever small prey they preyed upon. Maybe there was a lot of food, and they could afford to get bigger. Getting bigger just to starve doesn't have much point, after all.
I just googled the question Why were dinosaurs so big? - there's quite a few pages, but it's still basically an unknown. So I'm simply guessing that there might have been a global parameter shift between now and then that helps explain it; and as the factor involves mass, then the requisite parameter is gravity. Of course it might be malarky, but from what I'm reading, nobody has any better ideas. X-)
Also, mammals were not very big at this time -- they were generally quite small. If gravity was less, back then, why wouldn't they be bigger too?
A third: After T R & Co ran out of steam, didn't animals start getting smaller? If gravity was less back then, wouldn't animals have continued to be XXXL?
Fourth: Their bones, muscles, and connecting tissues were proportionate to their size. Why couldn't very big muscles attached to very big bones with big connective tissue (tendons, ligaments, cartilage, etc.)? Maybe there were large ganglions located in the lower back to help coordinate tail and leg movement?
Five: How fast did T Rex & Co move? Presumably they didn't have to catch velociraptors for lunch; they probably looked around for a grazer and simple waddled up to it and bit it's head off.
If you look at alligators and crocodilia, none of them look like they'd be able to move very fast. But alligators manage to eat a few humans and their pets every now and then, some of them captured (by the gators) on dry land. There are alligators swimming around the flood waters of Houston right now, just waiting for some fat, luscious human to come bouncing along... SNAP!
Perhaps! But the giganticism of the sauropods seems on a different order to anything observed since.
It considers a different gravitational constant G, and doesn't reject it for enough reasons. If G was less back then, the Earth would be cold because it would be much further from the sun. The author seems unaware of that part, but at least is unwilling propose such a fundamental hit to physics.
Some interesting points: The descendents of dinosaurs are birds, most of which are already far less dense than water. Maybe the dinos had that as well and simply didn't mass as much as would an alligator that size.
In the end, a pretty plausible explanation relates to the know small variance in temperature between various latitudes back then. The poles were nearly as warm as anywhere else, suggesting a much more dense atmosphere which would buoy up the large creatures. Maybe Earth was more like Venus back then. What evidence do we have against that? Such a suggestion implies we're losing atmosphere quickly and there won't be much left after not too long. They already predict the oceans will be gone soon, but I thought it more from a warming sun than from just losing it all to space.
Interesting site, thanks!
You asked a straight question and I'm going to give you a straight answer.
The space dust that has fallen on Earth is 8 followed by 14 zeroes. In Kilograms. The mass of the earth is 6 followed by 24 zeroes. In Kilograms.This means that the size of earth increased by less than 0.000 000 001 percent. This is not at all significant, despite being more voluminous or heavy than all the buildings put together on manhattan island or all the pyramids in Egypt or the Great Wall of China, or the Great Barrier Reef near Australia, or... there is nothing in Europe I can think of which is similar in magnitude of size. All the cows of Europe.