Man's physical universe

xanabras

130 THE EARTH AS MAN'S ABODE

It is possible to determine experimentally the present rate at which salt

is thus being added to the oceans and also to determine the present

total amount therein. On the basis of such figures, the earth has been

calculated to be at least

100,000,000 years old.

Some of the earth's rock formations were laid down as sediment in

lakes and oceans. The maximum thickness of all such sedimentary

deposits if laid on top of each other would be about 500,000 feet. It

has been estimated that the average rate of sedimentation is about one

foot per 880 years. Such figures would place the age of the earth at

about 440,000,000 years, but they are based on so many variable

factors that the figures have little significance except in verifying the

conclusion that the earth is very old.

Of the nearly forty methods of estimating the earth's age, only one

is potentially accurate. This is the method based on the study of

radioactivity. Radioactive elements disintegrate to form lighter

elements. The present rate of this disintegration is definitely known.

By analysis, the amounts of the original elements and their disintegrated

products in

a given rock can be determined, and from these

data, assuming no initial products of disintegration, the age of the rock

can be calculated. A given stratum of rock can be recognized by the

fossils which it contains and by other methods, and the age of any

stratum which contains igneous rocks can be determined by determining

the age of these rocks by the radioactive method. Radioactive

examinations of the earth's crust indicate that its age lies between 1^

and 3}/2 billions of years. Einstein by other methods, however, calculates

that the earth is

10,000,000,000 years old.

Radioactive examination of many meteorites, some probably of

interstellar origin, has led some scientists to conclude that the whole

universe was born out of what came before it at about the same time

that our solar system is thought by some scientists to have originated,

about 1800 million years or more ago.

These various scientific estimates are based on methods which differ

in precision, but they all lead to the conclusion that the earth is very

old.

Lemaitre's Hypothesis Is That the Universe Started as One Giant Atom

about 1800 Million Years Ago.

Spectroscopic evidence leads to the theory of an expanding universe

because distant nebulae seem to be receding from us at terrific speeds.

Calculations based on the measured speeds and directions of motion

of many nebulae, assuming that they all started moving from one point

at a certain time in the remote past, being launched with their present

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