It has been known for a long time that the days at the end of the Mesozoic era were a little shorter than today’s, so that the solar year also had more days (various studies in the past reported a range of 370.3 to 375 days).[1] A more recent scientific work from 2020 probably definitively confirms this remarkable fact from the world of the last dinosaurs. It was published by a team of experts from the universities of Brussels and Ghent.[2] Their research material was the fossil shell of a rather inconspicuous bivalve from the rudist group, specifically a species Torreites Sanchezfrom a site in Oman, dated to the Late Cretaceous period.[3]
The head of the mentioned research was the analytical chemist Niels de Winter, who used precise lasers and created extremely small holes in the boxes of the mentioned rudists with his colleagues. The holes were only about 10 micrometers wide, about the size of a red blood cell. Thanks to this, the scientists managed to accurately calculate the amount of daily increments that were reflected on the inner texture of the box every Cretaceous day. Incremental lines showed that between 76 and 72 million years ago the solar year had a week longer than todaybut only for the number of days – the total length of the Earth’s orbit around the Sun has of course not changed significantly.
The difference was due to the only logical thing, which was the shorter duration of a day (that is, the rotation of the Earth on its axis). That was about half an hour faster than today and the last dinosaurs thus experienced days lasting only 23.5 hours (more precisely 23 hours and 31 minutes).The scientists were also able to detect the alternation of periods depending on climate changes within the framework of the isotope research of the elements present and thus determine the number of incremental lines within individual years. This makes them certain that the day at the end of the Cretaceous was about one fiftieth shorter than it is today. So dinosaurs wouldn’t recognize our wall calendars – if they could understand them – theirs would have seven days more every year!
Photo: Vladimir Rimbala
Scientist studying Late Cretaceous sediments. At that time, the days were still about half an hour shorter than today, and the solar year had more days. Credit: Vladimir Rimbala.
But that is not the only stimulating information that scientists obtained from the research of Rudist boxes. An interesting finding was also the temperature of the water in the place of existence of the Late Cretaceous animal. It came out to scientists at a full 40 °C in the summer and more than 30 °C in the winter. So the oceans were significantly warmer 75 million years ago than today (25 to 29 °C on average).[4] But let’s go back to the length of days during the last five million years of the Cretaceous. While the period of the Earth’s orbit around the Sun is constant for billions of years, its rotation around the axis gradually slows down. This is what causes days to be shorter in the past and individual years to have more days. According to some estimates, the day after the formation of the Moon by a giant collision lasted only 4 hours, and only after another 60 million years it was extended to 10 hours![5]
The main reason why the Earth’s rotation around the axis is lengthening is related to our Moon and its gravity. It causes tides with its tidal forces and gradually slows down the Earth with its gravitational pull. It is paying for this by its slow distance from the mother planet, at the current rate of 3.82 centimeters per year. Another interesting piece of information follows from this, that the Moon was closer to the Earth during the time of the dinosaurs. According to the calculations, it was about 383,000 (± 5,000) km, i.e. roughly only 1,500 kilometers less (a difference of around 0.4%) – we would not even notice such a difference. On the other hand, billions of years ago, the Moon was significantly closer to Earth and would have appeared truly gigantic in the sky.[6] Mesozoic dinosaurs, like us, could not experience that.
