New laser technology delves into Earth’s history.
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Earth turned faster at the end of the time of the dinosaurs than it does today, reports Phys.org, 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, according to the new study 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 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.
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.
“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. It’s pretty amazing,” said Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and the lead author of the new study.
Climate reconstructions of the deep past typically describe long term changes that occur on the scale of tens of thousands of years. Studies like this one give a glimpse of change on the timescale of living things and have the potential to bridge the gap between climate and weather models.
Chemical analysis of the shell indicates ocean temperatures were warmer in the Late Cretaceous than previously appreciated, reaching 40 degrees Celsius (104 degrees Fahrenheit) in summer and exceeding 30 degrees Celsius (86 degrees Fahrenheit) in winter.
The summer high temperatures likely approached the physiological limits for mollusks, de Winter said.
Full article here.
Tallbloke's Talkshop 
So what determines that the rate of spin should be 24 hours today? And why does the atmosphere spin faster?
Erl
It was the Babylonians who decided that there were 24 hours to the day, possibly because they had 8 or 12 digits. The silly molluscs apparently preferred the number 23.5 (only Douglas Adams knows why.)
“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.”
I’d love to know more about how the molluscs figured that out.
From the report:
De Winter’s careful count of the number of daily layers found 372 for each yearly interval.
Caption: Daily and seasonal layers are visible in a cross section through the specimen of the rudist clam Torreites sanchezi analyzed in the new study. The red box highlights well-preserved parts of the shell. The inserts show microscopic images of the daily laminae which are bundled in groups likely linked to the 14/28 day tidal cycles. Credit: AGU
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Moon-Earth connection: bundled in groups likely linked to the 14/28 day tidal cycles
The topic of earth rotation and length of day reminds of Ian Wilson’s classic presentation on the subject. Do long term variations of the sun drive climate change?
His article: http://www.lavoisier.com.au/articles/greenhouse-science/solar-cycles/IanwilsonForum2008.pdf
My synopsis and added context: https://rclutz.wordpress.com/2018/08/20/autumn-will-save-us-from-climate-change/
The speed of rotation at the equator is approximately 1,037 mph. The atmosphere moves in the same west to east direction but faster and fastest at the winter pole? In fact at the summer pole it reverses. The question is this? What is the origin of this spin and what determines it’s rate, both for the Earth and for the atmosphere at the winter pole?
Because in the history of the Moon, 70 million years is a blink in time, de Winter and his colleagues hope to apply their new method to older fossils and catch snapshots of days even deeper in time.
More data 🙂
“What is the origin of this spin and what determines it’s rate,…”
Read Pari Spolter’s The Gravitational Force of the Sun, 1993. The only caveat to her presentation is she does not define the origin of the force, which does not originate with the Sun.
Interesting, and touches on the paradox of Earth size and Moon size, increased mass of Earth yet Moon moving away, did Dinosaurs disappear unable to cope with increased gravity or atmospheric pressure.? And is the Moon increasing in mass with all the debris landing daily.
According to what I’ve read, the Earth was one quarter if present size 4 billion years ago and a day was 6 hours.
Ian Wilson’s work on LOD concerns lunar orbital effects on tides and ocean mass. See: The Changing Aspect of the Lunar Orbit & its Impact Upon the Earth’s Length of Day.
http://astroclimateconnection.blogspot.com/2016/03/there-is-natural-gleissberg-like-cycle.html
NASA’s LRO Reveals ‘Incredible Shrinking Moon’ 08.19.10
Newly discovered cliffs in the lunar crust indicate the moon shrank globally in the geologically recent past and might still be shrinking today, according to a team analyzing new images from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft. The results provide important clues to the moon’s recent geologic and tectonic evolution.
The moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the moon hot. The moon cooled off as it aged, and scientists have long thought the moon shrank over time as it cooled, especially in its early history. The new research reveals relatively recent tectonic activity connected to the long-lived cooling and associated contraction of the lunar interior.
[bold added]
https://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html
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Compression?
Oldbrew, I like the animation of the spinning Earth at the head of this post. So, my question is: Why does it spin? Can you tilt the axis of rotation to about 23.5 degrees please? Perhaps have an arrow to show the atmosphere moving in the same direction but faster at the winter pole.
Atmosphere version may not exist but there’s this…
The Earth spins because of conservation of angular momentum during formation
and the good news is that in the future we will be able to get more stuff done, because the days will be longer.
The conservation of angular momentum dictates that if the moment of inertia Iz (polar) increases with respect to Ix, Iy (equatorial) the earth spin increases. Meaning more ice loading at poles and less water at equator spin increases. And there will be variation in days/year.
That observation/evidence appears as a variation in the doorway ‘post-holes’ of the early megalithic calendars, though it is not a definite point. The newer method as it evolved did away with the ‘post-holes’; no longer needed; it was more accurate, plus offering the possibility of predicting accurately both equinox and solstice times.
That the year-length in days, and thus the LOD, varied, appears to have happened even during the last ten millennia. At least on this subject the rudist clams seem to concur.
‘the current 365’
Good grief! Ridiculous!
It’s 366. Plus change.
The earth rotates on its axis in 23 hours, 56 minutes.
The definition of a day as one rotation of the earth is bogus. It is one APPARENT rotation of the earth. While the earth is rotating, it is also marching around the sun.
You won’t see Orion in the summer sky. But it’s still there!