Making Eden - how plants 'terraformed' the Earth

Plants are everywhere around us  —  they provide us with the essentials for life. Yet, most of us rarely stop to consider them. In a new book called "Making Eden - How Plants Transformed a Barren Planet," Professor David Beerling chronicles the untold history of how plants evolved on land over millions of years and built the Earth we know today. 

Plants preceded animals onto land about 470 million years ago, and literally 'terraformed' the Earth — changing geochemical cycles and reshaping the world's atmosphere. In doing so they paved the way for animals to move onto the land. They're still maintaining our atmosphere and forming the base of the terrestrial food chain, and Dr. Beerling things we can learn lessons from the plant's remaking of our planet to repair the damage we're doing to it now.

Dr. Beerling is the Sorby Professor of Natural Sciences, and Director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield. Here's part of his conversation with Quirks & Quarks host Bob McDonald: 

This interview has been edited for length and clarity.

Bob McDonald: Now, you spent a little time at the beginning of your book suggesting that we take plants for granted — that we have what you call "plant blindness." What do you mean by that?

David Beerling: Plants are a ubiquitous feature of our environment. We tend not to notice them and realize that they support humanity both by providing food, but also by providing medicines, materials for construction and so on. They are absolutely essential to our existence.

BM: The subtitle of your book is "how plants transformed a barren planet." So tell me what life on Earth was like before plants made their way up onto the land.

DB: You can imagine unconsolidated soils that were very swampy and wet, and we have rivers that don't have river banks that are stabilized by plant roots and vegetation. So you have these braided fast flowing rivers that are subject to flash floods, and then you have an environment that's largely brown or grey, with perhaps thin green algal mats that appear and then occasionally dry out when the sun comes out. So it's a very desolate and windswept blank landscape, but also one I would say that as humans, it's quite difficult for us to imagine because in the whole of human evolutionary history, we've grown up in a vegetated landscape.

BM: What period was the earth barren?

DB: Prior to about 470 million years ago, there were no proper sort of bona fide terrestrial plants.

BM: There was life in the oceans though.

DB: Oh for sure we had. We certainly had plant life. We also had animal life in the oceans as well.

BM: Well, we have things in the ocean that are plant-like or like seaweed. But land plants seem to be really different from that. What were the first plants to make it up on land?

DB: Yes. There's a sort of common misconception that plants popped out of the oceans and arrived onto the shores of all of our coastal areas. But we now know from DNA sequencing studies that help us build the tree of plant life that terrestrial plants are more closely related to freshwater algae. And so it seems quite likely that the direct ancestors of plants evolved out of freshwater ponds and lakes. Perhaps you could imagine a scenario in which you had certain groups of algae that lived on the shores, and then as the pond starts to dry out, there are some genetic mutations or something that confers an adaptation or an advantage to some group of algae that enable them to survive a little bit longer. That provided the impetus for the first terrestrial plants to evolve.

BM: But they're going into a very, very different environment. What kind of adaptations did they have to go through to live up there?

DB: They were facing the challenge of water management — how to stay hydrated to enable their metabolism to proceed and not lose too much water so that they dried out. So essentially,  the earliest land plants were struggling to try and organize their water supply and now water loss in a way that balances it to enable photosynthesis and growth to proceed. 

Some of the early adaptations would be things like very fine root lengths to enable them to take water up into the stems and the tissues, and then they also have to regulate the loss of water, so they need these microscopic structures called stomata, which is essentially microscopic valves that adjust to be open and close to enable the plant to control water loss. So the roots suck the water in then it goes up the stem. Then it's pulled through this loss of water out of the top of the plant by transpiration that's coming out of the stomata pores and taking in carbon dioxide. So they combine carbon dioxide and water out both through sort of schoolboy photosynthesis that produces biomass plus oxygen.

BM: So how then did we go from these tiny little things that aren't much more than dry land algae to the incredible variety of plants we see today? We've got ferns, we've got shrubs, we've got giant sequoia trees. 

DB: That's right. So from these very humble beginnings in the Ordovician-Silurian, within a few tens of millions of years, came the Devonian explosion in which you suddenly had most of the major body forms of plants appearing in the fossil record very quickly. So as you said, we have ferns, we have the forerunners to conifers, gymnosperms, and we see the appearance of trees very rapidly. 

You can really imagine that this is really related to the opportunities that were created by an empty landscape that once the plants had evolved the adaptations they need to succeed in these environments, then they had limitless supplies of water, they had a very carbon dioxide rich atmosphere to fuel photosynthesis, and they had abundant light because there was no self shading of pre-existing forests. So you had this wonderful ecospace for the plant life to radiate and to explosively diversify, and we see the signature of that diversification in the plant fossil record.

The entire audio interview is available at the top of this page