As per the news reports in March 2020, a study published in the American Geographical Union’s journal Paleoceanography and Paleoclimatology provided insights into a time when the earth was much warmer. The scientists analysed the fossil of a little mollusc that lived for nine years in a shallow seabed. The fossil, found in the dry land in the mountains of Oman, is seventy million years old. Its study has given the following clues about the behaviour of the Earth a long time ago:
- Earth Spun 372 times a year 70 million years ago, compared to the current 365. It means the day was 23½ hours long, compared to 24 hours now.
(ii) This new measurement informs models of how the moon formed and how close it has been to Earth over their 4.5 billion-year gravitational relationship.
(iii) The study looked at daily and annual variations in the mollusc shell and concluded that Earth spin has slowed down over time. Previous climate reconstructions have also typically described long-term changes over tens of thousands of years.
(iv) The ancient mollusc namely, Torreites sanchezi, belonged to an extinct group called rudist clams. It belonged to the late Creteceous, some 65 million years ago when dinosaurs went extinct.
(v) The mollusc grew very fast, laying down daily growth rings. Using lasers on a single individual; the researchers sampled tiny slices and counted the growth rings accurately, which determined the number of days in a year 70 million years ago.
(vi) Importantly, the Earth orbit has remained the same. However, if there were a calendar, then the year would have been 372 ‘days’ long with each ‘day’ half-an-hour shorter than one day today.
(vii) Today, Earth’s orbit is not exactly 365 days, but 365 days and a fraction also due to which our calenders have a leap year. The lead author, Neils de Winter, a geochemist from Vrije University, Brussel said they were pretty sure about the accuracy of number of days, i.e., 372, however, the exact number could be 372.25 or 371.75 just like 365.25 days nowadays.
(viii) Friction from ocean tides, caused by Moon’s gravity, has slowed Earth’s rotation. Consequently, the days get longer and the Earth’s spin slows, the Moon moves farther away, at 3.82 cm per year. If this rate is projected back in time, the Moon would be inside the Earth only 1.4 billion years ago, which is impossible because the Moon has been with us much longer. It means the Moon’s rate of retreat has changed over time.