[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Sauropods vs. Gravity

At 03:28 PM 3/3/2002, you wrote:
Although I don't agree with Colin's thoughts on possible past gravity
fluctuations, I feel obligated to point out that lower gravity in the past does not imply that the earth was physically smaller then, or that it is more massive now.  For example, a phase change in the core, mantle, or crust could cause the earth to be smaller in diameter now, which would result in greater gravity at the surface (I don't believe to have been the case).  For a given mass, a smaller radius in the past would have resulted in greater surface gravity then.  If the earth were smaller in the past, and less massive, the surface gravity could have been either less or more, depending upon how much smaller and how much less mass.  Planets smaller than the earth can have greater surface gravity, even with
less mass than the earth, just as they can have lower surface gravity with more mass.

I am confused.  I thought gravity was based on mass, not volume.  Changing the diameter of the Earth would not change its mass.  How would the gravity change?

I looked up this topic and found this from the USGS:

"Gravitation is the force of attraction between two bodies, such as the Earth and our body. The strength of this attraction depends on the mass of the two bodies and the distance between them." [emphasis theirs]

What am I missing?

Darryl Jones  <dinoguy@sympatico.ca>
For information on tyrannosaurids and
cool activities and information for kids,
visit my webpage at: