Viewing 19 posts - 1 through 19 (of 19 total)
  • Gravity…
  • DickBarton
    Full Member

    Has gravity always been this ‘strength’? Could it have been more/less when dinosaurs were around?

    scotroutes
    Full Member

    Has the mass of the Earth changed much in the past few millenia? If so, where did it go/come from?

    cloudnine
    Free Member

    Maybe there was suddenly less gravity and many of the dinos just floated off into space..

    goldfish24
    Full Member

    No, it has not always been this strength.

    Gravity on the surface of earth is directly related to the mass of the earth, and to how far you are from the centre of mass.

    The earth is not a perfect sphere, its a bit fat at the equator… It’s an oblate spheroid. So gravity is weaker at the equator than the poles. Earth hasn’t really got much heavier or lighter since dinosaur time, but continents have moved around and mountains risen and fallen, so the gravity where you are now has changed.

    scotroutes
    Full Member

    You’re confusing cause and effect. If all the dinosaurs floated off into space then there would be less gravity…..

    jonahtonto
    Free Member

    gravity fluctuates all the time as do most ‘constants’ but i guess your leaning towards the fact they were big and therefore would have more difficulty moving around. if so the question should really be ‘was there more o2 in the atmosphere enabling more efficient use of muscles?’

    edit; there are some really interesting things being discovered about gravity at the moment. which is good since it is a very little understood force. for instance, gravity escapes black holes so therefore it must move faster than light, which doesnt

    molgrips
    Free Member

    The earth was basically the same mass for most of its life. Although it’s been accreting stuff over the years through meteorites and whatnot landing on it.

    Pretty sure oxygen content has varied quite a lot in the years though.

    peterfile
    Free Member

    It was definitely stronger back in the day.

    ampthill
    Full Member

    There will be some small variation from things like the reduced rate of rotation of the earth through its life. the day started at 6 hours

    However dinosaurs were like well recent. Died out 65 million years ago, Earth is 4500 million years old

    As mentioned above it varies with altitude and latitude. But not by much. I once had a great online discussion about whether we could detect this variation with a simple pendulum. My guess was that we could with some care. I’ve had students get g as 9.80+/-0.01 m/s2 with a small weight, a meter stick a stop watch and a bit of string

    Rorschach
    Free Member

    I think it should be renamed ‘Grabity’.
    That is all.

    piemonster
    Full Member

    Kaesae to the forum

    CountZero
    Full Member

    if so the question should really be ‘was there more o2 in the atmosphere enabling more efficient use of muscles?’

    There were certainly periods when the atmospheric oxygen content was very much higher:

    Why Were Prehistoric Insects Huge?
    Aug. 8, 2007 — Alexander Kaiser, Ph.D., of Midwestern University’s Department of Physiology, Division of Basic Sciences, was the lead author in a recent study to help determine why insects, once dramatically larger than they are today, have seen such a remarkable reduction in size over the course of history.
    “There were hundreds of ideas to explain the small size, but none of them could be proven,” Dr. Kaiser said. To test their theory that it was an insect’s respiratory system that limited its size, he and his colleagues launched an extensive study using beetles and fruit flies.
    The study, much of which was performed at Illinois’ Argonne National Laboratory, involved the examination of various beetles’ respiratory systems, using new x-ray beam technology to help determine how they breathe.
    Findings show that Dr. Kaiser and his colleagues are on the right track in their theorizing. Insects breathe through a network of air filled tubes that deliver oxygen directly to the cells. These tracheal tubes, especially in the leg, take up more room in larger beetles.
    “More than 300 million years ago, there was 31 to 35 percent oxygen in the air,” Dr. Kaiser said. “That means that the respiratory systems of the insects could be smaller and still deliver enough oxygen to meet their demands, allowing the creatures to grow much larger.”
    Dr. Kaiser and his team plan to conduct similar studies in the future using more ancient species such as dragonflies, since beetles and fruit flies are considered relatively “new” species in comparison.

    Goliath beetles and sphinx moths would be described as large by just about anyone living today, but some prehistoric insects would dwarf these evolutionary descendants. During the Paleozoic era, the Earth teemed with giant insects, from dragonflies with wing spans measured in feet, to mayflies nearly 18 inches in breadth. While over a million insect species live today, truly giant insects no longer exist. Why did giant insects live in prehistoric times, but disappear from the Earth over time?

    Answer:
    During the Carboniferous and Permian periods, atmospheric oxygen concentrations were significantly higher than they are today. Prehistoric insects breathed air that was 31-35% oxygen, as compared to just 21% oxygen in the air you’re breathing as you read this. Atmospheric oxygen is the single most limiting factor on insect size.

    The cells in your body get the oxygen they need to survive via your circulatory system. Oxygen is carried by the blood, through your arteries and capillaries, to each and every cell in your body. In insects, respiration occurs by simple diffusion through the cell walls.

    Insects take in atmospheric oxygen through spiracles, openings in the cuticle through which gases enter and exit the body. Oxygen molecules travel via the tracheal system. Each tracheal tube ends with a tracheole, where the oxygen dissolves into the tracheole fluid. The O2 then diffuses into the cells.

    When oxygen levels were higher, as in the prehistoric era of giant insects, this diffusion-limited respiratory system could supply sufficient oxygen to meet the metabolic needs of a larger insect. Oxygen could reach cells deep within the insect’s body, even when that insect measured several feet long. As atmospheric oxygen decreased over evolutionary time, these innermost cells could not be adequately supplied with oxygen. Smaller insects were better equipped to function in a hypoxic environment. And so, insects evolved into smaller versions of their prehistoric ancestors.

    Sources:

    Dudley, Robert. (1998). Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance. The Journal of Experimental Biology 201, 1043–1050.
    Dudley, Robert. (2000). The Evolutionary Physiology of Animal Flight: Paleobiological and Present Perspectives. Annual Review of Physiology, 62, 135–55.

    darrell
    Free Member

    cant remember the name but there’s an old book by Kurt Vonnegut that prattles on about gravity changing

    was funny

    kayak23
    Full Member

    Gravity used to be stronger but has become less so these days, much like twiglets.

    molgrips
    Free Member

    “More than 300 million years ago, there was 31 to 35 percent oxygen in the air,”

    Yes, that’s what I was thinking, but it was well before dinosaurs. To put some perspective on those numbers, if you went back to dinosaur time, the giant insects would have been gone for much longer than the dinosaurs have now 😯

    Back then, there was loads of CO2 in the atmosphere, it made the planet pretty warm and because of all the CO2 plants grew like mad (they love CO2). Giant trees and all. Because plants also produce oxygen there was loads in the air, hence giant insects. The Earth looked just like that place Yoda lives. However all these trees growing like mad and then dying sucked all the carbon out of the air and turned it into coal… CO2 levels now are only just above starvation levels for plants. If you give them a bit more CO2 they grow like mad.

    hairyscary
    Full Member

    Gravity must be stronger than when I was a kid, because my wheels stay firmly planted to the ground nowadays.

    mrhoppy
    Full Member

    Gravity is stronger now than back in the day, it’s why I’m slower up hills.

    kimbers
    Full Member

    this should answer all your questions

    [video]http://www.youtube.com/watch?v=YUswKg7zQIo[/video]
    now it looks awesome, as in the visuals do, but obviously there should be NO SOUND!, Clooneys matured with age, but Bullock is a massive warning to avoid any movie (unless it features 3 Seashells) , Im really not sure I can handle 90 mins+ of her hyperventilating into a helmet- unless it all goes a bit ‘Fire In the Sky’ and they both get a good probing

    rogerthecat
    Free Member

    There are pockets of very strong gravity, I come across them regularly when I’m riding, causes havoc with the skin on my knees and elbows.

    The earth must be getting lighter, have you seen all the erosion the ramblers have caused round here?

Viewing 19 posts - 1 through 19 (of 19 total)

The topic ‘Gravity…’ is closed to new replies.