AGU: Shell Shows Days Were Shorter 70 Million Years Ago

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bystander
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AGU: Shell Shows Days Were Shorter 70 Million Years Ago

Post by bystander » Tue Mar 10, 2020 4:24 pm

Ancient Shell Shows Days Were Half-Hour Shorter 70 Million Years Ago
American Geophysical Union | 2020 Mar 09

Beer stein-shaped distant relative of modern clams captured snapshots of hot days in the late Cretaceous

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, according to a new study of fossil mollusk shells from the late Cretaceous. This means a day lasted only 23 and a half hours ...

The ancient mollusk, from an extinct and wildly diverse group known as rudist clams, grew fast, laying down daily growth rings. The new 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. ...

Subdaily Scale Chemical Variability in a Torreites Sanchezi Rudist Shell:
Implications for Rudist Paleobiology and the Cretaceous Day-Night Cycle
~ Niels J. de Winter et al
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