Study on Rudist Clams
Scientists recently studied an ancient molluscan (Torreites sanchezi) fossil to estimate the length of day, 70 million years ago.
The Torreites sanchezi is a species of molluscan (shelled animal) that belongs to an extinct group of clams called the rudist clams. They lived during the Late Cretaceous period, about 70 million years ago. These clams are noted for growing very fast and they developed growth rings on a daily basis.
Length of Earth Day
The scientists studied the growth rings using lasers to determine the number of days in a year during that period (70 million years ago). The earth spun 372 times a year (372 days) back then, compared to the current 365 times (365 days). This implies that the days back then had 23.5 hours compared to the current 24 hours.
The study also shed light on the evolution of the Earth-Moon system. The earth has slowed down its spinning since earlier times. As the earth spins slower, the moon moves farther away from the planet at the rate of 3.82cm per year. The scientists used the growth ring data to propose that the lunar retreat rate has not been constant over time.