Dinosaur days were a half-hour shorter

According to new research, the earth turned faster at the end of the time of the dinosaurs than it does today, rotating 372 times a year, compared to the current 365, which eventually means a day lasted only 23 and a half hours.

The findings from a new study of fossil mollusk shells from the Late Cretaceous, was published in AGU’s journal Paleoceanography and Paleoclimatology. The ancient mollusk, from an extinct and wildly diverse group known as rudist clams, grew fast, laying down daily growth rings. The study used lasers to sample minute slices of shell and count the growth rings more accurately than human researchers with microscopes. The growth rings allowed the researchers to determine the number of days in a year and more accurately calculate the length of a day 70 million years ago. The new measurement informs models of how the Moon formed and how close to earth it has been over the 4.5-billion-year history of the earth-moon gravitational dance. The new study also found corroborating evidence that the mollusks harbored photosynthetic symbionts that may have fueled reef-building on the scale of modern-day corals. The high resolution obtained in the new study combined with the fast growth rate of the ancient bivalves revealed unprecedented detail about how the animal lived and the water conditions it grew in, down to a fraction of a day.

The research study analysed a single individual that lived for over nine years in a shallow seabed in the tropics – a location which is now, 70-million-years later, dry land in the mountains of Oman.

The ancient mollusks had two shells, or valves, that met in a hinge, like asymmetrical clams, and grew in dense reefs, like modern oysters. They thrived in water several degrees warmer worldwide than modern oceans. This result suggests daylight was more important to the lifestyle of the ancient mollusk than might be expected if it fed itself primarily by filtering food from the water, like modern-day clams and oysters, according to the authors. The length of a year has been constant over earth’s history because earth’s orbit around the sun does not change.

But the number of days within a year has been shortening over time because days have been growing longer. The length of a day has been growing steadily longer as friction from ocean tides, caused by the moon’s gravity, slows earth’s rotation. The pull of the tides accelerates the moon a little in its orbit, so as earth’s spin slows, the moon moves farther away. The moon is pulling away from earth at 3.82 centimeters (1.5 inches) per year.

Precise laser measurements of distance to the moon from earth have demonstrated this increasing distance since the Apollo programme left helpful reflectors on the moon’s surface.

(HT Media)