29 Nov Dinosaurs and the Moon
Argentinosaurus. Image Credit: https://www.rareresource.com/argentinosaurus.htm
CrowdScience takes questions from members of the public and puts them to experts to answer. The question “Did the moon have a greater impact on life on earth at the time of the dinosaurs than it does now?” grabbed my attention, as it dovetails nicely with one of Discovery’s activities, “Weighing Giants”, which uses modelling, maths and physics to estimate a dinosaur’s weight. CrowdScience also interviewed UNE Palaeontologist Dr Nic Campione (along with UK scientists Dr Darren Baskill and Professor Sara Russell, and US Professor Neil Comis) to help unpick the answer. As it turns out, the answer is not a straightforward “yes” or “no”.
There are three things to think about. Firstly, how do we calculate the weight of a dinosaur? Secondly, how much closer to earth was the moon? Thirdly, would this difference have affected a dinosaur’s weight?
Image credit: https://dinosaurpictures.org/Argentinosaurus-pictures
Dr Nic Campione, who specialises in how much the dinosaurs may have weighed (amongst other fascinating palaeo ideas) explained that the giant sauropod dinosaur Argentinosaurus was somewhere between 60 and 120 tonnes, compared to an elephant which is about 6 tonnes. Calculating dinosaur weights is a complex thing. If plenty of bones of a certain dinosaur are found, we can create a 3D model of that dinosaur, but mostly we don’t find that kind of fossil record. Then there is a calculation that can be done using the size of weightbearing bones and the size of the animal. Other things must be accounted for, such as whether the bones are air-filled, or the size of the lungs, which can impact its weight. Nic thinks that the enormous size of sauropods was possibly impacted by the climate rather than the distance to the moon.
100 million years ago, when dinosaurs inhabited earth, the moon was closer to earth than it is now. The moon is moving away from earth at about 4cm a year (Dr Darren Baskill describes it as about the same speed as our fingernails grow), so during the time of the dinosaurs, the moon was about 4000km closer. Which seems a lot, but as the moon is currently 384,000km away from us, it was only 1% closer in the time of the dinosaurs.
We know that the moon exerts a gravitational force on the earth, and we see that in the tides. There is a high tide on the side of the earth closest to the moon caused by the moon’s gravity, and on the opposite side, there is another high tide created by the motion of the earth. Dr Neil Comis also reminds us that the land is also affected by the gravitational pull of the moon and becomes a few centimetres higher when the moon is directly overhead. Of course, this is not obvious to us compared to tides of the sea.
In addition, the high tide on earth is also affecting the moon – gravity is a two-way street. In fact, the high tide on the surface closest to the moon, pulls the moon in the same direction it orbits, causing it to spiral away from earth.
So…If we could go back in time with a very accurate, and very large, set of scales, and if we could convince a dinosaur to stand on them, would the stronger pull of the moon decrease its weight compared to now? Well yes, the moon pulling ‘up’ on the dinosaur would have made it weigh slightly less (although not a significant amount).
But …when the moon was on the opposite side of the earth, the gravity would have pulled down harder on the dinosaur, making it heavier!
Finally… As the moon orbits the earth in an oval shape, sometimes it is closer to earth than other times (think Supermoons and how large the moon looks then). That difference is more than the difference between moon’s distance from earth during the time of the dinosaurs compared to now.
So, the answer to this complex question is “yes” and “no”! To learn more, listen to the full program here BBC World Service – CrowdScience, How did the Moon affect the dinosaurs?