Privileged Planet: how plants changed it (Introduction)

by David Turell , Wednesday, September 13, 2023, 17:12 (227 days ago) @ David Turell

An enormous review:

https://www.livescience.com/planet-earth/plants/once-again-innovation-and-proliferation...

"Plants are so ubiquitous on land that it's hard to imagine their absence, but for almost 90% of Earth's history, there was no life on land, or at the very least no plants. Land plants emerged a little more than 400 million years ago, which compared with the 4-billion-year history of life on Earth, is comparatively recent.

"This evolutionary leap allowed them to become (arguably) only the second group of organisms to radically change the world, a full 2 billion years after the first, cyanobacteria, oxygenated the planet. Their world-changing predecessors precipitated a Great Oxidation Event that was likely the biggest environmental disaster in history — but also set the stage for all multicellular life on Earth. Land plants did not have quite this big an impact, but theirs was greater than any other group of organisms in the intervening two billion years.

"For reasons I'll explore below, plants' evolutionary innovations are, in some ways, best understood through their connection to their cyanobacterial predecessors, and to the next group of world-changing organisms to evolve — humans. That connection lies in Life's Formula, the five elements that make up all living things: hydrogen, oxygen, carbon, nitrogen and phosphorus.

***

"As with the cyanobacterial revolution that oxygenated the planet, the evolutionary innovations that allowed plants to complete the slow march landward revolved around access to the elements in Life's Formula. A first, and critically important, step was to bring the photosynthetic machinery from the ocean with them. The chloroplasts in plant leaves — the place where photosynthesis occurs — have their own DNA. It's the DNA of photosynthetic ocean bacteria that, long ago, merged into plant cells. Chloroplasts are thus an example of endosymbiosis — an organism within an organism. As a result of this endosymbiosis, the chemical reaction of plant photosynthesis is the same as cyanobacteria photosynthesis. It uses the same machinery. That is why land plants pump out oxygen during photosynthesis in the same way cyanobacteria do.

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"Because land plants inherited their photosynthetic machinery from their ocean-dwelling, single-celled ancestors, they use the same hyper-efficient, water-reliant photosynthesis. They split water using the energy from sunlight, capture CO2, and produce sugars to build their cells (and oxygen, by evolutionary accident). But every moment they open their leaves tiny pores to let CO2 diffuse in from the air they lose scarce water out through the same conduit. This is a scarcity ocean-dwellers don't have to deal with.

***

"By colonizing the continents and moving to the source of the elements whose availability constrained their ocean-dwelling ancestors, land plants set themselves up to become the second great world-changers.

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"Land plants made three key innovations. First, they found a new way to capture sunlight and thus carbon. In this case the innovation wasn't a new biochemical reaction but the movement of this reaction to a new place. Second, they evolved a way to withstand water scarcity on land by building root networks and partnering with fungi (among other things). Finally, they became miners, digging for critical rock derived nutrients that were, and remain, scarce in the ocean. Their innovations in getting water and nutrients allowed their wild proliferation. (my bold)

***

"Eventually, plants' innovations pulled enough CO2 out of the air that the greenhouse effect began to weaken. The pan-tropical Earth, which had supported great forests across most of its land, began to cool. It is unclear how long the process took before Earth chilled enough to have ice ages.

***

"The process driven by plants was slow: a drip, drip, drip out of the bank account of CO2 in the air and a transfer of that carbon below ground. Some of that carbon was gradually compressed, concentrated, and turned into coal. Then, 300 million years after those tropical trees succumbed to environmental changes of their own making, the next world-changing organism, humans, discovered that carbon-rich bank account.

"We began burning this stored carbon at a rate never before seen in the history of our planet. We used the energy that burning produced to build dams and capture water, allowing us and our crops to stay hydrated on land. We used that energy to industrially fix nitrogen and mine phosphorus to fertilize our now-irrigated farms. And we too, are changing the world, even faster than our predecessors. But like them, our success, and environmental peril, is tied inextricably linked to the elements in Life's Formula."

Comment: all living organisms modify our Earth. The environment we have now has ice at both poles. We humans arrived long after a very tropical Earth moderated. dhw's obsession with 'humans and their food' is shown by this very long article to be a false premise. All of that food development as a giant bush of life, was actually a process of evolving the Earth through time. Very long read filled with many biochemical insights.