The Emerald Planet

The Emerald Planet: How Plants Changed Earth's History by David Beerling
My rating: 3 of 5 stars

This is something in between a history of plants on Earth, and a set of essays on that theme. It does start with the development of leaves, and then moves on to the plants' creation of massively high oxygen levels in the Carboniferous (the era of dragonflies with 5' wings) so the first two chapters felt like it would be a tour of plant evolution.

This is probably far too broad a topic, and in any event is not what we get. Nothing about the evolution of flowers or the period worldwide redwood forests, for example. Instead the themes are not merely what was important to plants, but when plants were important to the climate, or even our understanding, through fossils, of the climate. This is a fascinating picture of a dynamic planet, constantly changing in response to a dance between geological processes and plants, which respond and then change the atmosphere and soil in turn.

The chapters cover the science with some technical detail, but also the history of the science, and in some cases the quirks of the scientists. The implications of these sorts of changes to modern day climate change is mentioned more than once, but happily the science is treated as interesting on its own terms, rather than a tool for the present. Some of the research referenced seems cutting edge, which is actually both a complement and a concern--I'd expect at least one or two of the stories to change as we learn more about the distant past. (Not a knock on Beerling, who is quite up front about uncertainties.) My only other nitpick is my ebook was missing the full color plates.

For my own reference the chapters are below--spoilerized, although the stories are tens of millions of years old, it's probably better to just read the book.

• The evolution of leaves took place only when CO2 dropped. This was the "Cambrian explosion" of plants, but before CO2 dropped thin photosynthetic stalks were better at managing water loss and heat.
• Oxygen level shot up in the Carbiniferous. In general oxygen varied between 15 and 30% or so in the Earth's history; contrary to Lovelock increased fires did not stop oxygen from reaching high levels.
• The Permian extinction was probably caused by the collapse of the ozone layer, possibly by volcanic emissions passing through halogen containing layers (in Siberia?) to create the aerosol can from hell. (Note: Beerling does not use the term 'aerosol can from hell.')
• Increased CO2 (and global temperatures) cleared the way in the late Triassic for the dinosaur era, probably caused by more geological upheaval.
• The forests of the poles were not evergreens, but deciduous. Interestingly the six months of darkness wasn't apparently the driving force for them dropping their leaves, as it's expensive to regrow them; rather, it was the ability to grow quickly in the summer months that let them outstrip their more stately conifer brethren.
• The Eocene warm spell (50 million years ago) probably hit peaks not driven by CO2 so much as amplified by methane hydrate release. No, there's nothing to worry about with the IPCC projections, why do you ask?
• Grasses and weeds use a C4 pathway rather than a C3 pathway in photosynthesis. This is far more efficient and they can do it by concentrating CO2 in organelles beyond normal atmospheric levels. Furthermore, once grasses get going (maybe eight million years ago) they increase the frequency of fires, killing trees and opening up more areas for colonization by rapidly growing grasses. (So they are nasty "disruptive innovators" destroying the world's traditional forests . . . some stories hit too close to home.)

This was all well presented. I'd recommend this if it sounds at all interesting; the fact that I can type things like "High oxygen levels in the Carboniferous" a month after finishing the book is a credit to Beerling's ability to fit each chapter's facts into a coherent narrative, rather than my fading