When the Earth Was Green: Plants, Animals, and Evolution’s Greatest Romance

When the Earth Was Green: Plants, Animals, and Evolution’s Greatest Romance by Riley Black

Riley Black’s The Last Days of the Dinosaurs made my top ten books of the years when it came out (if you haven’t read it, you absolutely should), so I was excited to read her follow-up When the Earth Was Green: Plants, Animals, and Evolution’s Greatest Romance. I’m happy to report that like its predecessor, it’s an impressive work of popular science marked by wonderful prose and an engaging voice.

The book opens with Black on a dig, frustrated by not finding any sign of the T-Rex fossils she was hunting for, but then happily surprised when she pops up a sheet of sandstone to reveal a beautifully captured fossil leaf that “looked almost new, as if it had just recently wafted down on a later summer breeze . . . I could see everything down to the tiny, branching veins.” Musing on her find, she notes her realization that “What is a Tyrannosaurs without a forest to conceal its shadow as it stalks? What is a Triceratops without a buffet of ferns and cycad fronds to eat?” And thus this book, which takes 15 key moments in time when plants and animals, separately and together within their inseparable connections, changed our planet.

Black starts 1.2 billion years ago in Arctic Canada with the algae Bangiomorpha, which was not only one of the first life forms to make its own food (via photosynthesis) but one of the first to reproduce by sex, allowing for more and faster variety amongst descendants, which meant more adaptability to changing conditions and a greater flowering of life. In clear, lucid language Black concisely explains the rise of photosynthesis, how chloroplasts likely formed, the creation of stromalites (evidence of early life), the increase in atmospheric oxygen, the shift from asexual to sexual reproduction.

From there it’s a jump to 425 million years ago in Oman and shore-dwelling low plants akin to liverworts. Unassuming plants that are the beginning of massive changes due to the ripple effects of oxygenating the air, taking carbon out of the air and burying it as they decompose, weathering down the rocks freeing minerals like calcium to be taken up by creatures that use it for skeletal features, increasing fires, cooling the planet by reducing the carbon dioxide in the atmosphere and more. Meanwhile, Black reminds us, invertebrates were already crawling around amongst the sand and rocks and plants.

This pattern continues for a total of 15 time slices, including the rise of forests 307 million years ago thanks to the repurposing of lignin inside plant bodies, creating habitats for giant insects and protomammals like Melanedaphodon; an Apatosaurus munching, thanks to an evolved digestive system, on giant conifers, ferns, ginkgoes and monkey puzzle trees in Utah 150 million years ago; and the growing expanse of grasslands in Nebraska 34 million years ago, and their impact on creatures that remained wedded to the forest, like Megacerops, and those who adapted to the new open areas — early horses like Mesohippus.

In each section we get a vivid sense of the world in that particular time and place, clear explanations of changes in plant and animal types and how those plants and animals interacted in their environments, adapting to or driving further changes in the planet. The focus on interaction and the cascade effects are particularly fascinating and one way this book stands out amongst similar titles.

Another way is Black’s prose, which is wonderfully engaging, always crystal clear, and at times nicely lyrical. Technical language is employed, but relatively minimally and always within a clarifying context. Here is an example of one of her most poetic passages:

Riley Black

The entire forest seems to ask for quiet, a long shhh among the trees. Another great autumnal gust sweeps through the woods, shaking multicolored leaves in a susurration so all-encompassing it seems like a soft blanket of sound. Red, yellows, oranges, and a vanishing hint of green wave and flutter, a few leaves carried off to tumble and twirl along the wind.

Another plus is the notes section that follows the main text, where Black goes into a bit more detail about some points in each chapter, such as explaining her choice of representative creatures/plants and clarifying what is directly confirmed by scientific findings and where she was more speculative. Don’t skip this section!

If I had any complaint or quibble, it’s that the format is more akin to a collection of brief science essays/vignettes, and I wouldn’t have minded a brief “interchapter” (very brief) that acted as some connective tissue by filling in those gaps between time periods via a big picture (what happened to the continents, the atmosphere, etc.). Just a sketch would have been enough for me. As it was, I had to constantly recalibrate as I started a new chapter. It wasn’t a big deal, but it was noticeable.

At the end of the book Black turns more personal, making a connection between her own transition to female and queerness and the wild diversity of life and nature. I’m sure there will be some who prefer she had left the personal out of a popular science book entirely, regardless of topic, and I’m sure there will be some who bridle at the queer/trans reference. I don’t and will never fathom the latter reaction. I have more understanding of the former, though I don’t agree with it; I’m a fan of scientists presenting themselves as people and enjoy the more personal touches. As for this specific example, I found this section both profoundly moving and inspiring, and that to me seems the goal, along with informing, of any good popular science book. And When the Earth Was Green is just that, a very good popular science book.