Recorded on: Sep 23, 2025
Carbon dioxide (CO2) is often seen as the problematic byproduct of modern lifestyles that threatens our planet’s stability – at least within conversations among environmentalists. But this perspective overlooks the fundamental role of CO2 in everything on Earth, from the food we eat to the houses we live in to our bodies themselves. Despite this reality, the carbon cycle as we know it has been interrupted in ways never before seen in Earth’s history. How could understanding the deep history of CO2, as well as humanity’s relationship with this controversial and vital molecule, help us prepare for the planetary changes ahead?
In this episode, Nate is joined by science journalist Peter Brannen, who reframes CO2 from an industrial pollutant to a miraculous substance whose critical role within the carbon cycle makes Earth habitable. Peter traces our planet’s history through the lens of CO2, including mass extinctions, Snowball Earth events, and the surprisingly stable Holocene period that has cradled human civilization. Peter also addresses humanity’s current impact on the carbon cycle, the complexity and resilience of Earth’s ecosystems, and the challenges we face as we push climate systems we don’t fully understand into unknown territory.
How is the carbon cycle unexpectedly connected to the origins of oxygen, dozens of major and minor mass extinctions, and even the beginning of civilizations? How do humanity’s current CO2 emissions compare to those of Earth’s past? And could understanding the deep time of geology inspire both cosmic wonder and precautionary action, subsequently pushing us towards better decisions for the future?
About Peter Brannen
Peter Brannen is an award-winning science journalist and contributing writer at The Atlantic, with particular interests in geology, ocean science, deep time, and the carbon cycle. His work has also appeared in The New York Times, The Washington Post, Wired, Aeon, The Boston Globe, Slate and The Guardian among other publications. His book, The Story of CO2 is the Story of Everything, was published earlier this year by Ecco, who also published his previous book, The Ends of the World, about the five major mass extinctions in Earth’s history.
Peter was a 2023 visiting scholar at the Kluge Center at the Library of Congress, and is an affiliate at the Institute of Arctic and Alpine Research at the University of Colorado-Boulder. He was formerly a 2018 Scripps Fellow at CU-Boulder, a 2015 journalist-in-residence at the National Evolutionary Synthesis Center at Duke University, and a 2011 Ocean Science Journalism Fellow at the Woods Hole Oceanographic Institution in Woods Hole, MA. His essays have been featured in the Best American Science and Nature Writing series and in The Climate Book by Greta Thunberg.
Show Notes & Links to Learn More
The TGS team puts together these brief references and show notes for the learning and convenience of our listeners. However, most of the points made in episodes hold more nuance than one link can address, and we encourage you to dig deeper into any of these topics and come to your own informed conclusions.
00:00 – Peter Brannen Works + Info
03:04 – CO₂ is the cause of most mass extinctions
04:15 – Humanity’s tribal nature, U.S. polarization on climate
04:29 – Excess CO₂ in the atmosphere hurts key plants and crops more than it helps
05:03 – Carbon-based life, CO₂ provides the control knob for the planet’s temperature and the ocean’s chemistry
05:37 – Carbon cycle (slow and fast)
06:48 – Gaia vs Medea Hypotheses
07:13 – Terrestrial life can only live in a narrow temperature range, CO₂ concentration 50 million and 20,000 years ago
07:35 – Rock weathering cycle keeps the planet habitable
08:00 – Current atmospheric CO₂ is around 430 parts per million, Gigatons of CO₂ in atmosphere and ocean
08:18 – Humans emit 100-300 times more CO₂ than volcanoes
09:00 – 60Fº temperature drop over next ~50 years if all CO₂ vanishes from atmosphere
10:01 – Long-term decline of carbon in Earth’s system
10:32 – Benjamin Mills: Earth Evolution Modelling
11:53 – Snowball Earth (More info)
12:25 – Hadean Eon (time between creation of Earth and Origin of Life), History of Earth, Geologic time scale
13:08 – Geoengineering: CO₂ injection into basalt rocks
14:24 – Snowball Earth to Cambrian explosion
15:54 – Origin of Life theories, Hydrothermal vents
16:44 – Dissipative structures
17:23 – Economic Superorganism
17:44 – Origin of life researcher Mike Russell, His related work: Origin of Life
17:52 – “Turbines” of mitochondria (Animation), Electron transport in mitochondria, Pumped storage hydropower
19:03 – Fossil fuels and the carbon cycle
20:10 – Howard Odum and 4th Law of Thermodynamics – Maximum Power Principle (More info)
20:53 – Holocene and stable climate
21:05 – Humans are unique: Capacity for Abstract thought, Problem solving intelligence, Moral mechanisms, Default Mode Network organization
21:19 – CO₂ decline that led to the Ice Age cycles, Milankovitch Cycles
22:05 – 34 million years ago, Antarctica got an ice cap for the first time
22:50 – Homo genus origin (More info), Age of mammals
23:18 – Humans of the ice age and fire
23:37 – Climate swings made agriculture difficult
23:50 – Climate-resilient crops
24:25 – Interglacial, If humans weren’t here we’d be going into another Ice Age
25:48 – End-Permian Mass Extinction, Temperature change during that time
26:34 – DJ White (Reality Roundtable #11, TGS Ep #51) Holocene (Anthropocene) Thermal Maximum, PETM
27:15 – Earth system sensitivity
27:55 – Ocean acidification during PETM, PETM caused a coral reef collapse and saw some extinctions, Ocean cores (white to red) from North Atlantic Ocean
28:16 – International Geological Congress Working Group on the Anthropocene
28:30 – Core from Crawford Lake clearest signal of the Anthropocene layer
30:45 – Humans are emitting CO₂ at a rate 10 times faster than the End Permian and the PETM
32:25 – It takes millions of years to build up fossil fuels in Earth’s crust
33:30 – Water vapor vs. CO₂, Water cycle is increasingly erratic
37:00 – Oil companies sponsor paleontological research
37:30 – Oceanic CO₂ absorption, Forest CO₂ absorption
39:10 – Antoine Lavoisier: Gerbil in ice experiment – Combustion and aerobic respiration
40:00 – Geological history of oxygen, Oxygen deoxygenation
40:30 – Photosynthesis is a necessary condition for oxygenating the planet but is not sufficient
40:40 – Fossil fuel formation and oxygenation
41:05 – Photosynthesis might have evolved three and a half billion years ago, but oxygen didn’t rise to breathable levels until only the last few hundred million years
41:24 – Carbon hides in sediment, keeping oxygen in atmosphere
43:30 – Predictions for future global temperature
47:30 – Little Ice Age wasn’t global
49:01 – Pliocene, Comparable amount of CO₂ as today
49:30 – Climate expert consensus
51:35 – China going all in on producing solar panels/EVs and selling to rest of world, Also running more coal than ever before
53:10 – Agriculture in a 3Cº world, U.S. food supply chain distance
55:20 – William Ruddiman and his “early Anthropocene” hypothesis (More info)
58:00 – Some powerful actors provide misinformation to the public, Past fossil fuel misinformation campaign
1:00:00 – Coral reef projections, Ove Hoegh-Guldberg + TGS Episode
1:01:20 – Tom Chi, TGS Episode
1:05:00 – Luke Kemp (TGS Episode #153, #194), Nancy McWilliams & Reid Meloy (Reality Roundtable #19), Frankly on Mean vs. Median Human, 1% of population is psychopathic
Teaser image credit: Author supplied.