Re: Does anything make the earth grow heavier as time goes by?

Dear Katie,

Your question is really about the Earth’s mass, not its weight.  Please 
bear with me while I explain a few difficult ideas.  Mass is a fundamental 
property of all matter.  All objects, including the Earth, the Sun and 
stars, you and even a single atom, have mass.  Sir Isaac Newton, the great 
scientist who founded the science of physics, defined mass as the measure 
of how difficult it is to accelerate an object:  the more massive an 
object, the more difficult it is to accelerate it.  Gravity is the 
phenomenon by which objects with mass interact with one another:  all 
masses attract all other masses, which means, for example, that you and 
even the most distant star in the universe exert a gravitational 
attraction on one another (although in this case it would probably be too 
weak to measure!).

Weight is a measure of the force of the gravitational attraction exerted 
by the Earth upon an object.  Weight is proportional to mass, which means 
that the greater the mass of an object the greater the force of 
gravitational attraction it exerts.  Therefore, you will weigh less than, 
say, a house, because the house has more mass than you, and so the Earth’s 
gravitational force on the house is greater than it is on you.  Also, 
weight varies with distance, so that if you are standing on the Earth’s 
surface you will weigh more than if you were on board an airplane flying 
high above the surface.

Now, the weight of the Earth could be defined as a measure of the force of 
gravity exerted on the Earth by the Sun.  But if the Earth existed deep in 
space, so remote from the Sun or any other star that the force of gravity 
exerted on it was tiny, then the Earth would be almost weightless.  
However, the Earth would still have mass, no matter where it was located!

So, I come back to my first point, which is that your question is really 
about the Earth’s mass.  The answer to your question is that the Earth’s 
mass is constantly increasing, and has been ever since the Earth was 
formed.  Every meteorite or grain of dust that falls onto the Earth from 
space increases the amount of matter on the Earth and, therefore, 
increases its mass.  The solar system started out as a giant cloud of gas 
and dust in space, and the Sun and all the planets including the Earth 
were formed by the clumping together under their mutual gravitational 
attraction of this dust and gas.  As each clump grew larger so its mass 
increased and the gravitational force it exerted increased, so that it 
swept up even more material and grew even larger, and so on until it had 
gathered most of the material within its orbital path.  During this 
process of accretion the Earth’s mass grew rapidly.  Afterwards and until 
the present day the amount of material that falls on the Earth is very 
small compared to the mass that the Earth already has, but even so the 
Earth’s mass continues to grow very slowly.

I hope this answers your question.

Best wishes,

David Scarboro