TECH & SCIENCE

BY ROSIE MCCALL ON 3/10/20 AT 11:11 AM EDT

DAYS ON EARTH WHEN DINOSAURS LIVED WERE HALF AN HOUR SHORTERTHAN THEY ARE NOW, ANCIENT FOSSIL REVEALS

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fossilized shell from the late Cretaceous has provided evidence that it takes the Earth a half-hourlonger to spin on its axis today compared to 70 million years ago. This supports the predictions

made by astronomical models.

Scientists writing in Paleoceanography and Paleoclimatology worked this out by analyzing daily growthrings in ancient mollusks. Using various measurements and dating techniques they were able to countthe number of days in a year and even measure light variance across a single day.

The results suggest a dinosaur's year would have been 372 days long—a week longer than ours—buttheir days would have been almost half-an-hour shorter.

"We have about four to five datapoints per day, and this is something that you almost never get ingeological history," lead author Niels de Winter, an analytical geochemist at Vrije Universiteit, said in astatement. "We can basically look at a day 70 million years ago. It's pretty amazing."

The basis of the study is a 70-million-year-old Torreites sanchezi mollusk, which spent more than nineyears living in a shallow seabed in what is today entirely dry land in Oman's mountains.

Lasers were used to drill holes in the shell just 10 micrometers in diameter—a size a little larger thanthe width of a red blood cell. The study's authors say this technique enabled them to count daily growth

Fossil rudist bivalves (Vaccinites) from the Al-Hajar Mountains, United Arab Emirates.

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rings with more accuracy than methods involving microscopes.

The method yields very detailed information about changes in the environment at a scale of just days,de Winter told Newsweek.

"The 'snapshots' of climate we can obtain in this way teach us how warmer climates, such as those inthe Late Cretaceous, 70 million years ago, affect seasonal differences in temperature and extremeweather events," he said.

The study was also the first to provide "convincing evidence" that mollusks like T. sanchezi had asymbiotic relationship with photosynthesizing species, said de Winter. Patterns in the rings suggests theshells grew faster in the day than at night and was driven by solar (rather than lunar) cycles. Theresearchers believe T. sanchezi co-existed with a second species that lived inside the mollusk and fedon sunlight—like algae found in giant clams today.

T. sanchezi contained two uneven shells attached on a hinge—a little like a twenty-first centuryasymmetrical clam. It lived in reefs, submerged tropical waters, and would have served a similarfunction in their ecosystem as modern-day corals. That is, before the creatures died out during theCretaceous–Paleogene extinction event that killed non-avian dinosaurs 66 million years ago.

"There's nothing like it living today," said de Winter.

The researchers say that while it has been predicted by astronomical models that days 70 million yearsago were shorter than they are now, this is the most accurate calculation of how long a year would havebeen during the late Cretaceous.

As Newsweek previously reported, days gradually get longer as Earth's gravitational grip on the Moonweakens—a phenomenon that currently takes place at a rate of 1.5 inches (3.82 centimeters) per year.As the Moon retreats, the Earth's rotation on its axis longer to complete as the friction from tidal forceswanes.

Information about the rotation of the Earth is important for those wanting to understand how the moonformed and how the relationship between the Earth and moon has changed over time, de Winterexplained. Data like that described in the paper could be used to help test astronomical modelsmeasuring how the length of a single day has changed over the course of the planet's history.

"Deciphering fingerprints of length of day in a rudist (the T. sanchezi) is a unique tool to reconstruct theevolution of the Earth-Moon system," Mingsong Li, Assistant Research Professor in the Department ofGeosciences at Pennsylvania State University, told Newsweek.

The study of the length of a day is a cornerstone to understanding past climate change at a muchhigher temporal resolution (daily) in comparison to the millennial‐ to million-year-scale currently used tomonitor paleoclimate changes, said Li.

This article has been updated to include additional comments from Dr Niels de Winter and ProfMingsong Li.

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