Beach Read #2 was THE UNIVERSE WITHIN, by Neil Shubin.
It's a delightfully detailed and nerdy, yet approachable take on "We're all star stuff". There's all kinds of fun facts and revelations for the lay person, like the conclusion that the earth is three-quarters of the way through its life expectancy. Ruh-roh.
Here's another fun excerpt (Quick context: when North America and Africa broke apart 200 million years ago, the Atlantic Ocean formed. More ocean = more algae, which slowly fueled more oxygen into the atmosphere, "lifting the lid" on future big mammals, whose cells need more oxygen to flourish):
Since the fetus receives all of its oxygen from the mother, there needs to be a way that oxygen can be transferred from the mother's blood. The transfer is facilitated by a steep gradient between the concentration of oxygen in the maternal blood and that of the fetus: under these conditions, oxygen will travel into the fetus. Importantly, the oxygen content of the mother's blood has to be sufficiently high to enable this transfer in the first place.
This constraint means that mammals with a placenta do not easily develop above fifteen thousand feet altitude.
Tellingly, the oxygen at these altitudes is equivalent to that in the atmosphere at sea level 200 million years ago, before the Atlantic Ocean formed.
The more things change, the more they stay the same.