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Less gravity on Earth when Dinosaurs roamed because all mass in universe was closer?

  1. Oct 8, 2008 #1
    When looking at dinosaurs and how they lived many millions of years ago it is clear that they must have done so under less gravitational pull from earth. But it is possible that earths gravity was the same when they roamed the planet but what allowed them to weigh less was that all mass in the universe was closer to earth at that time and thus exerting more of a pull in the opposite direction of earths gravity. As newtons Law clearly states all mass pulls on each other and as the distance between 2 objects increases the gravitational pull decreases. So as the universe expands it pulls less and less agains't earths gravity and thus all objects on earth now weigh more. Is this a possible thoery or are other objects in our universe to far away to change the weight of objects on earth as they move farther away?
     
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  3. Oct 8, 2008 #2

    ZapperZ

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    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    Whoa!

    How long ago did the dinosaurs live? And what is the difference of time period when compared to, say, the age of the universe? Do you think a difference of less than 0.001% is THAT noticeable?

    You need to provide justification for the very first line that you typed:

    When looking at dinosaurs and how they lived many millions of years ago it is clear that they must have done so under less gravitational pull from earth.

    This is neither clear, nor has it been published anywhere.

    You may also want to re-read the PF Guidelines that you have agreed to.

    Zz.
     
  4. Oct 8, 2008 #3
    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    The distances in the Universe are way too big. Plus of course there is about the same number of stars in any direction so the forces cancel each other mostly.
    The graviational pull actually was a little lower back then because the earth rotated more quickly i.e. the days were shorter. But that is only a small effect.
    If the dinosaurs were still alive today they could grow just as large as they did 100 million years ago.
     
  5. Oct 8, 2008 #4
    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    Well, as an attempt to add some relevance to this thread we could discuss wether the Earths gravitational pull actually was noticeable weaker - say - 200 million years ago due to the simple fact that our planet gains tonnes of mass every day. I think as a rough eatimate it is generally accepted that today Earth gains somewhere between 10^6 and 10^8 kg / year due to space debris falling down on the planet surface. Thats not a lot, and if we assume this rate to be constant the dinosaurs would have experienced pretty much the exact same g-pull we do today. But on the other hand... per definition Earth has gained ALL its mass from space during the last 5 billion years, so the mentioned rate can't possibly have been constant throughout Earths lifetime. At some time in prehistory it must have grown a lot faster. The trouble is figuring out how much more mass Earth has gained in the last few 100 million years.

    Cheers,
    Michael
     
  6. Oct 8, 2008 #5
    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    I don't think that the gravity on Earth in the time of dinosaurs was much different from today's gravity. When the solar system formed (about 4.5 billion years age), the planets gained most of their mass in first 100 milion years. The rate of gaining mass has been decreasing since then, because there ammount of (non-planetary) material flying around the Sun was decreasing. So the Earth's mass in the time of dinosaurs must have been about the same as today.
    The radial acceleration because of Earth's rotation in the time od dinosaurs (about 100 milion years ago) was also very small in comparison with g, since we know that it was smaller than g even when the Earth formed.
    Of course the theory about the gravity of stars which cancels the Earth gravity makes no sense. Among other problems, a contribution of an outside mass can never have a direction away from the Earth center on the whole surface, since the force of gravity has zero divergence.

    Obviously the dinosaurs had physiological adaptations, which enabled them to carry their weight despite their size. Although I can't quite understand, how could their musles produce so huge pressures. It seems incredible that they could hold more than 10 meters long necks and tails in horizontal position.
     
  7. Jun 3, 2011 #6
    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    Hello,

    I was told by someone I respect dearly that the gravity was much lower back then. I believe its been proven that in recent times besides the maximum mass for flight, the largest you can get isnt much larger then an elephant. Besides the mass of the earth it has more to do with where the solar system was in the galaxy rather than any universal effect. The galaxy does move very slow but it does move. Im not an expert at all but find these things very fascinating. Prehistory is so hard to assume or study.

    Thanks
     
  8. Jun 3, 2011 #7

    ZapperZ

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    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    Fortunately, this is a science forum, and in that light, we do not consider "I was told by someone" as a valid reference. You and that respected person should produce a peer-reviewed paper for citation. Otherwise, this is an unverified hearsay.

    And in case you didn't notice it, you resurrected a thread that has its last activity in 2008!

    Zz.
     
  9. Jun 3, 2011 #8

    Drakkith

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    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    The gravity of the earth was NOT less than it is now to any significant degree. A small amount of accumulated or lost mass due to space dust and whatnot will NOT make a noticeable difference.

    The likely reason for the increase in size is addressed here in an article on Sauropoda: http://en.wikipedia.org/wiki/Sauropoda

     
  10. Jun 3, 2011 #9

    Drakkith

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    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    The amount of matter that the earth has accrued over the last 100 million years pales in comparison with the total mass of the earth. Again, the gravity of the earth has changed very very little since the dinosaurs lived.

    Also, plant growth and lava flows don't create new MASS, they use already existing mass.
     
  11. Jun 3, 2011 #10

    ZapperZ

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    Re: Less gravity on Earth when Dinosaurs roamed because all mass in universe was clos

    This thread has deteriorated into wild speculation with no support from peer-reviewed papers. It is now in violation of PF Rules that everyone had agreed to. It is now closed.

    Zz.
     
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