When a Day Was Short
from the book, "Our Fascinating Earth"
When a Day Was Short
Many scientists agree that during the primal stages of the earth the moon was much closer to this planet than it is a present, possibly as close as 12,000 miles. At that period of earth history, a lunar month, the time it takes for the moon to revolve around the earth, would have been as short as six and a half hours.
The gravitational effects that the earth and moon had on each other must have been tremendous. They resulted in a braking effect, and with the passage of time the axial rotation of each celestial body was slowed down considerably. The centrifugal force of the earth resulted in pushing the moon farther and farther away from the earth. Even now, over four billion years later, it is still receding at the rate of about four inches per month.
Strangely, the evidence for this phenomenon is provided by living and fossil organisms. Many modern coral species show well—defined growth bands. Between major growth bands are very fine bands that always number 365. Obviously one fine band of growth occurs every day of the year; the coral adds to its skeleton on a daily basis.
Certain fossil coral species show the same characteristic and thus record in their skeletons their prehistoric rate of growth. However, they contain many more daily growth rings than modern species, indicating that there must have been a greater number of days in a year than there are at present. Such evidence suggests that the earth in prehistoric times must have rotated more rapidly than the current rate of once in twenty—four hours.
A study of corals of 370 million years ago shows the same growth ring characteristic. Since they contain 400 fine daily bands, the implication is that at that time a year was 400 days long!
The older the fossil geologically, the greater the number of growth bands it contains. By computing this rate of growth, many scientists now believe that during the primal stage of the earth, about 4.6 billion years ago, a day was only about four and a half hours long!