MadSci Network: Earth Sciences

Re: Is gravity on earth increasing

Date: Mon Nov 8 21:16:37 1999
Posted By: Layne Johnson, Undergraduate
Area of science: Earth Sciences
ID: 941584780.Es

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 

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 

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 

I don't know enough abour reptiles or amphibians to say how they would 
fare.  Again, I suggest resubmitting the question under the category 

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 

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 
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.]

Current Queue | Current Queue for Earth Sciences | Earth Sciences archives

Try the links in the MadSci Library for more information on Earth Sciences.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.