How This Prehistoric Clam Tracked the Moon

Daisy Hernandez
Photo credit: AGU

From Popular Mechanics

  • A bivalve fossil has surprised researchers by providing a look at daily life 70 million years ago.
  • Torreites sanchezi, the prehistoric bivalve, formed sedimentary bands along its shell—similar to the rings we use to age trees. Using advanced analysis methods and technology, researchers were able to measure factor such as weather and water temperature.
  • The fossil also reveals changes in the relationship between the Earth and the moon.

Fossils are incredible gateways to the past, showing us what life was like many millions of years ago. One such find is Torreites sanchezi, a bivalve shell belonging to a group called ‘rudists,’ that’s 70 million years old and has been acting as a clock of sorts during the years it spent buried within the earth.

These ancient bivalves were similar to modern clams in that their shells had an impressive growth rate—an entire layer per day. The laminae—growth bands which are similar to tree rings—grew in accordance with the weather giving researchers an unprecedented look at what a day looked like several thousand millennia ago.

But it wasn’t just weather; T. sanchezi also captured snapshots of water temperature and chemical makeup, in essence, freezing several moments in time throughout the day. Niels de Winter, a geochemist and professor at Belgium’s Vrije Universiteit Brussel (VUB), told Science Alert that the bivalve offers a unique look at the past.

“We have about four to five datapoints 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,” de Winter said in a press release. “It’s pretty amazing,” he adds.

Exactly how does de Winter and his team able to effectively study this prehistoric fossil? The short answer is that they used several analysis techniques, including microscopy and x-rays. They also analyzed isotopes and ion charges in relation to ionic mass.

According to a study published in Paleoceanography and Paleoclimatology, “a combination of layer counting, spectral analysis of chemical cyclicity and chemical layer counting shows that the rudist precipitated 372 daily laminae per year, demonstrating that length of day has increased since the late Cretaceous, as predicted by astronomical models.”

What else did the team learn? For one, they discovered that their specimen lived to be around nine years old and, in a surprising turn of events, found that they could use the bivalve to model “the evolution of the Earth-Moon system.”

The bivalve fossil explains the reason for the shorter amount of days in a year. The total amount has decreased from 372 to 365 days—something we can thank the moon, and subsequently, the ocean. The resulting friction from ocean tides has been ever so slightly slowing Earth’s rotation down.

“The pull of the tides accelerates the moon a little in its orbit, so as the Earth’s spins slows, the moon moves farther away,” shares an American Geophysical Union (AGU) press release. This means that the satellite is slowly moving away from earth at 1.5 inches a year. For now, this is one thing we don’t have to be too worried about—it’ll be billions of years before the moon’s distance begins to affect life on Earth.

As for de Winter and team, the plan is to apply these analysis methods on additional fossils in the hopes of catching more daily snapshots of what life on earth was like so, so long ago.

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