Researchers Analyzed Fossilized Shell to Determine the Length of a Day 70 Million Years Ago

The Earth rotated faster back at the end of the dinosaurs period than it does currently, rotating 372 times per year, while now it only completes orbits of 365 days, as per new research of fossil mollusk shells dating back to the late Cretaceous period.

This means that a day only lasted 23 and a half hours back then, the study published in AGU’s journal Paleoceanography and Paleoclimatology claims. The ancient mollusk, coming from an extinct and incredibly diverse group called rudist clams, grew fast, developing daily growth rings. The new paper used lasers to analyze minute slices of the shell and count the rings more precisely than human researchers with microscopes.

The Length of a Day 70 Million Years Ago

The growth rings enabled the scientists to estimate the number of days in a year and, more specifically, calculate the length of a day 70 million years ago. The new measurement suggests models the way Moon formed and how close to our planet it has been throughout the 4.5-billion-year background of the Earth and Moon gravitational pattern.

The new research also discovered supporting evidence that the mollusks hosted photosynthetic symbionts that may have powered reef-developing on the level of modern-day corals. The high resolution received in the new study mixed with the fast growth rate of the ancient organisms unveiled unique details about how the animal lived and the water status it grew in.

“We have about four to five data points per day, and this is something that you almost never get in geological history. We can basically look at a day 70 million years ago. It’s pretty amazing,” said Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and the lead author of the new paper.

The Shell Lived More Than Nine Years

Chemical analysis of the shell depicts ocean temperatures were warmer in the late Cretaceous period than earlier estimated, reaching 40 degrees Celsius (104 degrees Fahrenheit) in summer and surpassing 30 degrees Celsius (86 degrees Fahrenheit) in winter. The high temperatures in the summer most probably approached the physiological limits for mollusks, de Winter said.

“The high fidelity of this data-set has allowed the authors to draw two particularly interesting inferences that help to sharpen our understanding of both Cretaceous astrochronology and rudist palaeobiology,” said Peter Skelton, a retired lecturer of palaeobiology at The Open University and a rudist specialist not involved in the new study.

The new research investigated a single organism that lived for more than nine years in a shallow seabed in the tropics, a place which is now a dry land in the mountains of Oman.

“Rudists are quite special bivalves. There’s nothing like it living today,” de Winter said. “In the late Cretaceous especially, worldwide, most of the reef builders are these bivalves. So they really took on the ecosystem building role that the corals have nowadays.”

The new technique used by the researchers focused a laser on tiny parts of the shell, making holes 10 micrometers in diameter. Trace materials in these small samples unveil data about the temperature and chemistry of the water back when the shell developed.

The analysis generated accurate measurements of the width and number of daily growth rings, including seasonal patterns. The team of researchers also used seasonal variations in the fossilized shell in order to detect years.

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