## Meteorites, Cosmic Dust, and Mass of Earth

• 7.1k
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.

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.)
• 3.2k
Actually the opposite is true. Due to the natural loss of energy of the core, and the release of gases, the earth loses more than it gains, and it getting smaller.
• 2.7k
This is hilarious.
• 7.1k
any references for that? prepared to accept it but never heard it before.

This is hilarious.

Why?
• 2.7k

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.
• 7.1k
No, it's a serious question. Gravity is a function of mass, right? So a planet twice as massive as earth would have much greater gravity (I think twice as much but I don't know the physics).

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.

Are you afraid that if earth' mass increased, the earth' orbit will decay or would that it may even collapse out of orbit?

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.
• 2.7k
Ok, but what is the concern here, you haven't answered that? There is a lot of cosmic dust hitting the earth - tonnes of it actually if you check out CODITA - and to be sure the impact can certainly cause environmental phenomena and damage just as coronal rays during polar interaction influence auroras, but most of the space junk disintegrates as it collides with air and evaporates. It effects the stratosphere but not mass and in turn gravity.
• 3.2k
I don't know a whole lot about physics, might not be true.

http://gizmodo.com/5882517/did-you-know-that-earth-is-getting-lighter-every-day
• 7.1k
Well notice the first paragraph:

Earth is getting 50,000 tonnes lighter every year, even while 40,000 tonnes of space dust fall on our planet's surface during the same period. So, why are we losing so much weight? You will be surprised.

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.

Ok, but what is the concern here, you haven't answered that?

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.)

• 724
If I recall correctly, Carl Sagan contributed to some research on meteoritic dust accretion. He is mostly remembered for being a great science popularizer and a sort of generalist visionary, but he actually did some good down-to-earth (as it were) science as well.
• 7.1k
I used to like his TV show, although it wasn't broadcast regularly here in Oz. I also liked his book, Dragons of Eden, although he did tend towards scientism at times.
• 3.2k
So their estimate is 10x the figure quoted in the article I referenced.

A quick google search suggests that it is 40,000 and not 4,000.
• 2.7k
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.
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.
• 7.1k
I had heard that previously although I still don't think it would support the 'mass' hypothesis. I might float it over at Pysics forum (although I would leave out the dinosaurs).

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.)
• 7.6k
what was earth before our sun captured it?

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.

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

What about creatures from the Jurassic and Cretaceous that were not spectacularly large?
• 7.6k
It can survive in deep space

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.
• 2.7k
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.

• 7.1k
aha, so even tardigrades may not survive Scott Pruitt... :-(
• 1.7k

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
• 1.7k
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.

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
• 7.1k
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.

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.
• 1.7k

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
• 5.5k
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.

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.
• 1.7k

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
• 1.7k
Regarding the climate-effect of precession, I should add that it's a combination of two things actually:

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
• 7.1k
Maybe the dinosaurs were so big because food was so abundant before the impact.

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.
• 1.7k
It isn't so much a question of nutrition, as how the skeletal and muscular dynamics of creatures that large could hold up. 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.

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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• 1.7k
we watch "Jurassic" Dino-movies every week.

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
• 7.6k
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.

And by what theory could gravity be different 250,000,000 years ago? Had Newton overlooked something?
• 7.1k
Damned if I know, BC. All I'm saying is the preponderance of gigantic animals - even including dragonflies and cockroaches - seems to suggest that something was very different in the Jurrasic era.
• 7.1k
Besides wasn't it the nature of gravity about which Newton famously declared to 'feign no hypothesis'?
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