MadSci Network: Astronomy

Re: When did the world acquire the strong gravity we have today????

Date: Wed Aug 26 10:15:19 1998
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Astronomy
ID: 903975745.As

When did the world acquire the strong gravity we have today???? The Dinosaurs were too huge for their bones (which were not steel) and muscles to hold them up.

In S. America they cut a 200 ton stone from the solid rock and moved it over 200 miles over mountains terrain to top of the mountain. We have Stone Henge, the pyramids and endless other things.

The gravity must have been very weak during the early billion years.

Bill Stott (A real mad amateur scientist).

Hmm. I've heard this before... these are common misconceptions, Bill, and I'm glad I have a wide (yet shallow) background in this stuff so I can correct them. The bottom line is that the Earth's gravity has (so far as we can tell -- a word about that below) always been about the same.

1. The dinosaurs were not "too huge for their bones."

The dinosaurs had appropriate bone structure for their size. The engineering requirements for holding up that much weight are well-understood, both from human-built structures and from the study of modern animals like elephants. In fact (and get this!) weight estimates for various dinosaurs are based partly on the load that their skeletons can be calculated to withstand!

It is true that (rather unimaginative) paleontologists used to conjecture that, for example, sauropod dinosaurs (adults weighed up to 20 times as much as an African elephant) had to spend their lives mostly submerged to buoy up their weight, but in fact no dinosaur weighed as much as the modern blue whale (which is a water-living animal) and all big dinosaurs had load-bearing features in their skeletons adequate for holding up their weight.

One of the reasons I can say this with confidence is this: dinosaur trackways demonstrated that sauropods walked (never ran) with their legs underneath the body and their tails well up. Since this discovery, careful studies have been made of the load-bearing features of sauropod skeletons. It is true that sauropods could swim, but it is not true that they couldn't "pull their own weight" on land.

Here are sites for finding out more about dinosaurs:

2. So-called cyclopean structures did not require either low gravity or highly advanced technology to build.

I don't know anything about the stone in South America to which you refer, but it's been quite well-demonstrated that Stonehenge and the Egyptian pyramids were not beyond the reach of simple technologies operating under normal gravity. For example, PBS has been running a series of programs on ancient engineering projects in which modern-day engineers use tools and technologies available to the ancients to reproduce ancient engineering feats.

It's been pointed out before (by critics of "ancient astronaut" advocates like von Däniken) that we often underestimate the ingenuity of our ancestors, something that has been called "chronological snobbery."

Here are some good websites:

3. There is no reason to believe that gravity was weaker in the past.

First, there is a tremendous time difference between the dinosaurs (65 to 100 million years ago) and the ancient engineers (5 to 10 thousand years ago). Why would gravity, weak for so many years, get so much stronger so suddenly (that is, within the past few centuries)?

Second, people have considered theories of gravity in which the force of gravity was different (possibly weaker, possibly stronger) in the past. To date, all experiments have been consistent with the strength of the force of gravity being unchanged in the past.

You can bet that any information which would emphatically contradict current theories of gravity would be seized on by some young Turk of science, eager to make a big reputation!

No such information has turned up.
Dan Berger
Bluffton College

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