Scientists have a glimpse of the days and nights 70 million years ago
Imagine that you traveled to the Cretaceous period on a time machine. After a hard struggle to survive, you looked at your watch and sighed that it finally reached 23:30, and you successfully survived the next day in half an hour! At this moment, a Tyrannosaurus rex approached you from behind and poked your back with its short hand: “Brother, what do you think, isn’t it the next day?”
You ran all the way(2021 hermes bags), wondering as you ran: “What’s the matter, it’s a good 24 hours a day, why is it different?” Don’t panic, you should still be on earth. A recent study published in “Paleoceanography and Paleoclimatology” showed that in the late Cretaceous 70 million years ago, the earth’s day was only about 23.5 hours.
372 days a year
How does the rotation rate of the earth change over time? This is an interesting challenge for scientists. After all, we cannot go back to the past and directly experience and record the environment at that time. To understand this information, researchers can only look for clues from possible geological evidence like detectives.
The fossil of a bivalve named Torreites sanchezi provides high-resolution evidence for the restoration of the ancient earth’s environment. A bivalve is a mollusk with two symmetrical shells on the left and right sides of the body. The clams and scallops we eat now belong to the bivalves.
Bivalves have always been the research objects often used in paleoclimate and paleoenvironment(hermes outlet). Just like trees have growth rings, their shells also have growth lines or patterns. Due to different geographical locations, climate and other factors, the growth rate of trees will change, which affects the density and clarity of annual rings. Similarly, the growth lines of bivalves can reflect similar environmental conditions.
The fossil studied in this paper is very special. Its growth line is extremely accurate and well preserved. The researcher found through microscope observation that T. In the shell of sanchezi, light and dark patterns appear alternately, and each group of light and dark patterns is only about 40 microns thick. This is the trace of its growth day and night-the color of the shell grown during the day is light, and the color grown at night is dark. Day after day, these layers record every day 70 million years ago. The researchers also found that the ratio of the thickness of the light-colored and dark-colored layers exhibited a 15-day and 30-day cycle, which most likely represented the tidal and monthly cycles. On this basis, the researchers further identified the quarterly and annual cycles. Studies have shown that the individual has survived for at least 9 years, of which 4 years of growth lines are very clear and complete, providing excellent research materials.
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In addition to the color changes that can be seen with the naked eye, the researchers also measured the stable isotope (δ18O and δ13C) and trace elements (Ca, Mg, Sr, Li) content in the different layers of the shell, and also detected changes from these chemical indicators cycle. Combining the two methods, after further calibration, the researcher counted the ages in which the individual lived, which was 372±8.4 days in a year. Taking into account that the earth’s orbit is relatively stable, that is, the total duration of each year is basically the same, it can be calculated that there were only about 23.5 hours in a day 70 million years ago.
Clams that live with algae
T. Sanchezi lives in the shallow tropical sea. It is a kind of bottom-dwelling clams, so it is also called “fixed clams”. However, they became extinct together with the dinosaurs in the mass extinction event at the end of the Cretaceous about 66 million years ago. Up. The corresponding author of the paper, Niels de Winter, a geochemist at the Vrije Universiteit Brussel, Belgium, said: “The sessile clam is a unique animal. There is no similar double shell. They are like animals. In the late Cretaceous, these bivalves were widely distributed and were important reef-building organisms. Their role in the ecosystem at that time was similar to our modern corals.”
The research used a laser etching-inductively coupled plasma mass spectrometer (LA-ICP-MS), which can use a laser to lay a series of small dots with a diameter of only 10 microns from the shell, so as to continuously sample different parts of the shell for analysis The content of trace elements. When the shell grows, the environmental temperature and the composition of seawater will affect the proportion of its trace elements. Therefore, by measuring trace elements, it is even possible to restore the environmental changes every day at that time. Derwent was very surprised by this: “We can collect 4 or 5 data points in the growth zone every day. This accuracy is difficult to achieve in geoscience research. We basically saw that 70 million years ago Every day, it’s amazing!”
Studies have shown that the ocean temperature in the late Cretaceous was higher than previously thought, reaching 40°C in summer and over 30°C in winter. The author proposed in the study that the summer high temperature may have approached the physiological limit of mollusks.
Another interesting result brought by LA-ICP-MS is that the composition of the shell varies greatly during the day and night compared to the difference in different seasons. The growth rate of the shell is fast during the day and slower at night. In the study, the author pointed out that this kind of bivalve has a strong dependence on the daily cycle, which means that its growth is related to photosynthesis. Research suggests that this clam is likely to co-exist with some kind of organism that can carry out photosynthesis. This phenomenon is similar to the existing clams, it will co-exist with zooxanthellae-zooxanthellae can use the mantle of clams to effectively forage and reproduce, and clams can use zooxanthellae as a “small focus”. The consumption of maintaining a huge size.
Peter Skelton (not involved in this study), a retired professor at the Open University of the United Kingdom and an expert on sessile clams, commented: “At present, there is only discussion about whether stubbed clams symbiosis with photosynthetic organisms. Morphological evidence. And this discovery provides strong evidence for this speculation for the first time.” However, he also reminded that this conclusion only applies to T. sanchezi cannot be extended to other sessile clams.
The moon is moving away from us
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In the history of the earth, the number of days in a year has been decreasing, or in other words, the time of day has been increasing. This is because the tidal friction caused by the moon’s gravity will slow down the earth’s rotation speed, which is also called “tidal friction”. In contrast, the pull of the tide will make the moon slightly accelerate in its orbit, so while the earth’s self-transition is slow, the moon’s orbit is also moving away from the earth. Through the laser measuring instrument on the surface of the moon, the speed of the moon away from us is currently about 3.82 cm per year.
But scientists have proposed that in history, the speed of the moon away from the earth has not remained constant. The reason is simple-if you push back at the current speed, then 1.4 billion years ago, the moon should be inside the earth. Obviously, the current speculation on the moon’s age is far greater than 1.4 billion years (generally considered to be 4.5 billion years). The research mentioned in this article helps us understand a moment in the long evolutionary history of the Earth-Moon system.
Derwent and his colleagues expressed the hope that this method can be applied to more and older fossils in the future. If we can rely on similar methods to know the changes in the length of each day in the history of the earth, it may be able to help reconstruct the process of changes in the distance between the earth and the moon and the evolution of the earth and moon system.
