|MadSci Network: Earth Sciences|
Hello, Ross! The rate at which the earth accumulates mass is pretty slow compared to the generations of life. Since the dinosaurs died out 65 million years ago, the gravity pulling people and animals toward the earth hasn't noticeably changed. Do you remember the old Rocky and Bullwinkle cartoons? Mr. Peabody, the history professor, had a time machine called the "way-back machine". Had he gone back in time 65 million years ago, he would find the beaches less sandy, the oceans less salty, the oxygen content of the atmosphere different, and the temperature hotter, but he wouldn't be able to feel a difference in gravity. The changes in the earth's mass occur too slowly to be noticed in a mere 65 million years. But let's keep in the spirit of your question and imagine that from this point on, the earth's gravity will grow by 1% each decade. What would happen to people on earth? Before I answer, let me say that this question would be better answered by a medical specialist. I am a volunteer firefighter/E.M.T., and so I know a good deal about the human body, but you may want to resubmit this question to Mad Science again under the category "biology". The first thing we would notice would probably be an increase in heart attacks. It would be harder for our hearts to pump blood through our bodies. Next, we would notice that people's life spans were growing shorter. Even if we ignore the increased heart failures, other factors would combine to kill us off a little earlier. More bones would be broken, accidental falls would be more serious, etc. Our appearance would change. Those of us who had already grown to our full heights wouldn't noticeably shrink, but each generation of children would be a little shorter on average than their parents. We would wrinkle earlier in life. On the other hand, our bone density and muscular tone would both benefit from increased gravity. We would be shorter and stockier, and look older than we actually are. Sounds like J. R. R. Tolkein's dwarves in The Hobbit, doesn't it? As the years passed, dangerous accidents would happen. Skyscrapers and bridges would collapse in earthquakes they were built to withstand. Dams would burst. Rainstorms, and especially hail, would cause greater damage than they do now. Our diet would change. Apples and other fruit bearing trees would soon become extinct, the fruit unable to grow to maturity before falling to the ground in a rainstorm. Wheat and other edible grasses would need to be grown in protected enviroments. Since the necessary number of biospheres don't exist to grow all the wheat, rye, and other grains we need to eat, we would either need to build more or eat something else. Ground grown vegtables, such as potatos and onions, wouldn't be affected much by the change in gravity, and most likely farmers would turn to crops such as those to produce food. The process known as natural selection would progressively play a much greater role in our species than it does now. Children with weak hearts, weak bones, or poor balance would be less likely than others to live long enough to produce children of their own. So subsequent generations would have stronger hearts, stronger bones, and better balance, all passed down from their ancestors. Towards the end of human life, we'd be a species of very strong people. I believe our hearts would be the Achille's heel of the species. They couldn't grow strong quick enough to keep up with the increasing gravity. Adult hearts could probably survive better than infants'. By the year 2500 or so, babies wouldn't survive their first day out of the womb. That would bring mankind to its end. What about other forms of life on earth? Life in the water wouldn't be affected nearly as fast as life on land. The fish that live in the deepest parts of the oceans would survive the longest, for two reasons. First, they're most accustomed to life at great pressure; second, they could steadily migrate to shallow waters, where the pressure upon their bodies would feel the same as it did when gravity was weaker at a deeper depth. Insects would do quite well, having such a high strength/size ratio. Giraffes would to rather poorly, being unable to pump blood to their brains while standing upright, and having too much blood pressure in their heads when they bent down to drink water. Birds would take longer to mature for flight, putting a great strain in their parents to feed them longer. Scavenger birds, like condors, would die out quickly. They eat infrequently, and gorge themselves when roadkill is available. Such behavior makes it difficult for them to fly after a meal, and increased gravity would make them stuck on land for days. Coyote snacks! I don't know enough abour reptiles or amphibians to say how they would fare. Again, I suggest resubmitting the question under the category "biology". As a general rule, plants in the water would do better than plants on land, and the taller a plant species is, the earlier it would succumb to gravity. Of course, there are exceptions based on how straight the plant grows, how deep and strong its root system is, how thick its trunk is, and other factors. As for the moon, not much would change. Because the earth's gravity would be increasing steadliy, no sudden changes in orbit would occur. Assuming that the moon's mass remained constant while the earth's increased, the speed of the moon's orbit could increase, and the distance between here and there would decrease. The lunar month would be shorter than it is now. However, if you were standing on the moon and watching the earth's mass increase, you wouldn't be affected by it noticeably. If the moon had oceans like earth, the tides on the moon would be more pronounced than they are on earth, and they would grow more pronounced as the earth's mass increased. But a person on the moon wouldn't notice much except the inaccuracy of the wall calendar. Lunar time would be affected by a faster orbital period. Long before the moon and earth collided, life on earth would be dead, except perhaps on a microscopic level. But let's remember that the 1% per decade growth is very far removed from reality. Actually, the rate at which gravity becomes stronger is slowing down for two reasons. First, thanks to modern technology, more and more of the earth's mass is now in orbit, and not contributing to the pull of gravity we feel. This effect is only going to increase as space technology becomes more cost effective and efficient. Second, and far more significant, the number of bodies in the solar system that can collide with the earth is shrinking. Each time a comet orbits the sun, it looses some of its mass. That's what a comet's tail is, mass being shed. Of course, that mass just doesn't disappear. It has to go somewhere, and some of it comes to earth. But each time a comet orbits the sun there's less and less of it to shed. Arthur C. Clarke has stated that within a comparitively short time, there will be no more comets. (I'm sorry, but I can't remember which book or essay that was in.) Since each massive object in the solar system attracts other masses, eventually we'll arrive at a point where all the cosmic dust has been "vacuumed up." In fact, there's less dust floating free in the solar system now than there was when you started reading this answer. Yes, our home planet is getting more massive, but no, billions and billions of years would have to pass before the increasing mass made a difference in life on earth, and there's not enough free mass in the solar system to accumulate on earth to end all life here. Layne Johnson [Moderator note: Since the Moon is slightly more than 1% as massive as the Earth, a 1% increase in Earth's mass and gravity every decade means that slightly less than a Moon's worth of mass would have to be added to the Earth in a ten year time span. We would be buried in a matter of weeks at that rate.]
Try the links in the MadSci Library for more information on Earth Sciences.