The rise and fall of the dinosaurs by by Stephen Brusatte. So far this is my favorite book of the year. I would like to review this book by summarizing some cool things I learned about dinosaurs. They existed for 160 million years and all over the world there is lots of evidence of their behaviour.
One of my favorite facts about dinosaurs is that scientists are able to tell how long a particular dinosaur lived. Although some of them reached 40 years, most of them lived for about 30 years. The way they calculate their age is similar to how it is done with trees, this is by counting rings.
Basically what happens is that in dinosaurs, their bones continue growing over the span of their entire life. But nutrition is not always uniform. Food is more abundant in summer and therefore the bones grow faster in summer than in winter. This change of growing rate is seen in the bones as rings and then they just need to count the rings to establish the age of a dinosaur at the time of its death.
Another interesting fact about dinosaurus is their abrupt extinction. Luis Alvarez, winner of the Nobel prize of physics and his son Walter Alavez realized that an asteroid was the cause of the mass extension of the dinosaurs. Walter was studying the age of some geological layers of rocks in Italy and he wanted to figure out how to measure the age of a particular layer. They knew the age of the surrounding layers, but the intermediate one contained materials that were difficult to assess. Then Walter asked his dad for his opinion who in turn suggested looking for iridium in the rock samples.
Iridium is an extremely rare element on Earth and it slowly deposits on the surface of Earth through solar wind. This deposition process takes thousands of years but it happens at a rate that is more or less uniform. Therefore it can be used to measure the age of geological samples. They sent samples of the rocks to the lab for characterization and couldn’t believe there were such large quantities of iridium. The amount of iridium that they found was so large that it would take hundreds of millions of years to deposit on that particular layer of rock, which was clearly impossible since they knew with a good degree of certainty the age of the surrounding layers. Luis knew iridium is not present on Earth in such large concentrations and so he suggested the possibility that a big asteroid hit the Earth 66 millions of years ago and that event could be the main reason for the extinction of the dinosaurs. The impact of the asteroid caused catastrophic changes in the weather and in the geology of the planet, and the dinosaurs could not withstand these changes. A few thousand years after the impact all the dinosaurs disappeared for good.