Peter Brannen, a science journalist and former Gazette reporter, has spent most of his career writing about extinction.

His first book, The Ends of the World, discusses the Earth’s five major mass extinctions, including the most famous one that occurred 66 million years ago when a six-mile-wide asteroid pummeled 20 miles deep into land that is now the Yucatan Peninsula, initiating a global catastrophe that wiped out the age of the dinosaurs.

But it was actually the four other, lesser-known extinctions that interested Mr. Brannen most, all of which were caused not by massive space rocks falling into Earth, but by the planet itself releasing enormous amounts of carbon dioxide into the atmosphere through plate tectonics, biogeochemistry and other volcanic malfeasance.

Therein lies the dichotomy central to Mr. Brannen’s new book, The Story of CO2 Is the Story of Everything, which was published on August 26. The same primordial molecule that made life possible in the first place also has the power to destroy it.

“It’s funny, because in some ways, the extinction that everyone knows about was the least instructive. It was really just bad luck,” Mr. Brannen said of the dinosaurs. “But this new book spun out of that, because in the course of writing, I had to really come to terms with a lot of pretty hardcore geochemistry and understanding how these big planetary processes work. And I was just astounded by the fact that CO2 is central to all of them.”

The book traces carbon dioxide from its origins in the big bang to its role — possibly unfairly — as the central villain in today’s climate crisis, four billion years later. Over the course of 450 pages, Mr. Brannen describes how the infamous molecule is central to life on the planet, how its fluctuations in the atmosphere have caused terrestrial hellscapes that range from apocalyptic storms to a Hoth-like “Snowball Earth,” and how today we are in a lucky window that has allowed human life to flourish.

“This isn’t like other environmental problems or pollutants. CO2 is why Earth is Earth, and that was the revelation to me over the past decade, and why I wanted to tell the story that I was learning from geoscientists that has not really penetrated the public conversation about what this stuff is,” Mr. Brannen said.

Book was published on August 26.

The project of narrating CO2’s four-billion-year story involved about a decade of research, as Mr. Brannen met geoscientists everywhere from Carbon County, Wyoming to Scotland to Western Pennsylvania, where nearly 200 years ago coal barons began unleashing the potential of 500 million years of buried fossil energy to power the Industrial Revolution.

While Mr. Brannen argues, somewhat gratefully, that it would be nearly impossible for humans to release as much CO2 into the atmosphere as the event that caused the Permian extinction 250 million years ago, he notes that other extinctions happened on a geologic time scale, not a human one. In just 2024, humans released more than 40 gigatons of CO2 — 100 times more than all the volcanoes on the planet. That number was nearly zero in 1750, before the invention of the steam engine.

A sixth major extinction is happening at a pace heretofore unknown. And it is our own doing.

“The planet has such a narrow window to navigate. When CO2 has been 0.1 percent of the atmosphere, there have been crocodiles in Antarctica. And when it has been 0.01 percent of the atmosphere, there’s been an Antarctica’s worth of ice on North America and sea levels 400 feet lower,” Mr. Brannen said. “I came out of the experience mind blown that we were lucky enough to wake up on this planet with four and a half billion years of progress, and all this stuff has sort of been going perfectly. And we’re just trashing it all in a couple of decades.”

Before becoming a science journalist, Mr. Brannen was an English major whose favorite writers knew little of molecular geochemistry, cyanobacteria blooms or carbon emissions. But it was his time working as a reporter at the Gazette that familiarized him with environmental stories, including the work happening just four miles from the Island at the Woods Hole Oceanographic Institute, where he served as a fellow in 2011.

It was then that science writing crystallized for Mr. Brannen. He remembered the moment when a team of geologists studying a warming and ocean acidification event from 56 million years ago showed him a sediment core from the bottom of the North Atlantic, revealing 200,000 years of life, completely reorganized by climate change.

“That blew my mind,” Mr. Brannen said. “We often hear about climate change as this thing that’s theoretical, and it’s on computer models, and it’s all in the future. But there really is this incredible experimental record in the rock record, that if you’re a clever geochemist or geologist, you could just go and interpret.”

So what does the destruction and combustion of the 500 million years of weathered rocks, seashells, plankton, plants and animal fossils portend for Earth today — the burial of which, amazingly, is responsible for the surplus oxygen in our atmosphere?

“In a million years, the planet will be fine,” Mr. Brannen said. “Earth has seen worse than human beings before.”

But what about human beings?

“I’m a short-term pessimist and a long-term optimist, because it’s hard to squint at anything in the world today and be encouraged about how things are going,” Mr. Brannen said. “But I think eventually humans will find a more sustainable way to live on this planet, because either we will do it proactively ourselves, or the planet will make us.”