Human Evolution & CO₂

Daniel Lux
15 min readFeb 23, 2023


On October the 14th, 2012, a man fell to Earth. The man was Felix Baumgartner, who had traveled from the upper echelons of the stratosphere, 39 kilometers above sea level.

Before his free fall, viewers worldwide could/can see his body hover on a ledge and the Earth’s curvature below it. Out of view, the incessant sun burns and lights up the gases of Earth’s atmosphere, creating a thin blue line around the planet. Some will think, “this is what loneliness truly looks like”, while others feel the excitement of adventure.

The exact point of transition from Earth to space is to this day still debated, but as Felix Baumgartner looks through his space helmet at the azure blanket covering our planet, he bears witness to the one thing standing between life on Earth and the vast, cold darkness of space. And then he falls.

Felix Baumgartner becomes the first human, unaided by a vehicle, to break the sound barrier (1). After four minutes and 19 seconds of free fall through different atmospheric layers, a parachute releases, and he travels back to where his journey began, the Earth.

He makes a calm, controlled landing, safe under a blanket of just the right atmospheric composition that allows him to remove his spacesuit and breathe normally again. He has sought the limits of our existence, traveled towards the blurred, thin blue line under which a planet has existed for 4.5 billion years, and where life evolved from single-celled organisms to his kind, us, Homo Sapiens.

From a man on the edge of space to man on the edge of evolution, the defining line for the human branch on the hominin tree is equally blurred, not only by the distance of time but also by recent archaeological discoveries.

Homo Habilis, or ‘handy man’, from East and South Africa, lived about 2.3–1.65 million years ago and was believed to be the first of the hominin species to make a stone tool (2). This pioneering step earned him the name ‘Homo’, defining him as the first of our genus.

However, recent discoveries of stone tools are now attributed to the earlier hominin Australopithecus, making a case for the inclusion of this species on the Homo family tree. This discovery would date early humans back some 3.6 million years (3) and such a potential shift of the ancestral line by over 1 million years has, to this day, caused great scholarly and scientific debate. In Earth Years, however, the shift amounts to a mere 4 days and 21 minutes.

A number of stromatolites date back around 1.5 million years earlier than Australopithecus’ potential stone tools. The stromatolites hold key information about the atmosphere before and during the beginnings of the human race. Studies of the stromatolites tell us that the CO₂ content 5 million years ago was approximately 400ppm, and it reduced to around 300ppm some 3.5 million years ago, around the beginning of human evolution.

The CO₂ content stayed relatively low and stable for the following 2.5 million years, hovering around 280 ppm. The reduction from 400 ppm to 280ppm was a natural and biological decrease attributed to increased activity from CO₂-consuming plants. Their consumption of CO₂ slowly reduced the content in the atmosphere by about 120 ppm over a period of 4 million years — in Earth Years, two weeks,13 hours, and 28 minutes.

This relative CO₂ stability coincides with when human evolution took tremendous and definitive leaps, evolving from our very ape-like ancestors Australopithecus to Homo Erectus, ‘upright man’, whose first remains date back approximately 2 million years (4). Erectus is the earliest human ancestor believed capable of using fire, hunting, and gathering in collaborative groups, and evidence even point towards a display of care for injured group members.

And like our falling man Felix Baumgartner, Homo Erectus too sought the boundaries of existence. They ventured into unexplored territory, spreading throughout the Old World, and evolved into more complex species over the following 2 million years.

Blurred by uncertainties and new discoveries, the science tracing the ancestral line of the human race is still uncovering new things about our beginnings, not only as a planet but also as a race.

One constant throughout our muddled family tree is the atmospheric composition in which this extensively debated evolution occurred.

While unverified, it certainly gives cause for consideration that human evolution took place during a time when the CO₂ content remained relatively low and stable. This atmospheric stability may have created the particular conditions that our evolution required.

Ice Core drillings

While stromatolites provide critical insight into the CO₂ content during the first 2.5 million years of human evolution, we have even further detailed insight into the atmospheric composition for the last nearly 1 million years through ice core drillings.

Ice core drillings are samples removed from glaciers or ice sheets created by annual snowfall and melt cycles. The accumulated snow will press on the lower, older layers, increasing the density of the snow until it turns into firn, hard, and highly resistant ice. Each layer contains trapped material such as isotopes that provide vital information about past temperatures. Also existing within the solid core of ice are small pockets of history — tiny air bubbles that, when analyzed, enable us to determine levels of past atmospheric gases — for instance, CO₂.

The drillings can reach a depth of 3.2 kilometers and date temperatures and atmospheric gases back some 800.000 years. Fortuitously, this time span coincides with the very time when the most explosive evolution of humankind took place, where we transitioned from various archaic species to Neanderthals, Denisovans, and finally into the Homo Sapiens.

The ice core drillings show us that the great leaps in our evolution coincide with an extremely low and stable CO₂ content. A very regular pattern unfolds when we study the data extracted from the drillings, where CO₂ over 800.000 years (5) reaches a maximum of 300ppm, interspersed by periods of lower CO₂ content down to 175 ppm. These lower rates indicate the various ice ages that have seized our planet over the last million years.

Deep down below the artic snow, where layers of white create darkness upon white, ancient air bubbles are trapped in icy silence, holding pockets of our history in their icy grip. Each air bubble stores information about a given time in Earth’s life, and collectively they document a correlation between temperatures and CO₂ contents over the last 800.000 years’ glacial periods.

We know that the 120 ppm CO₂ reduction over a 4-million-year period was a biological lowering of CO₂ — nature at work. The low ppm levels during the last 800.000 years, as documented by the air bubbles from ice cores, are, in fact, physics at work.

Earth’s wobbly effect

Imagine a child, her eyes locked onto a spinning top. She observes it with such intent it would seem life depended on it. She’s anticipating what we all remember as children; a shift, a wobble that brings the spinning top out of what at first looks like an unwavering rotation.

Many believe the Earth’s orbit to be a constant, unwavering movement around the sun. However, our Earth wobbles too, and the lower CO₂ levels over the last 800.000 years occur with the onset of ice ages, driven by the periodic changes in the Earth’s orbit. The interaction of three orbital cycles changes the distribution of incoming solar energy. Precession, the small circles that the top of the spinning top makes. Obliquity, the angle of the Earth relative to the sun. Eccentricity, a measure of how oval the path of the Earth around the sun is. This interaction also called the Earth’s ‘wobbly effect, has a profound impact on the climate of our Earth (6).

Each orbital cycle has its own period. Precession has a 26,000-year period, shifting the orientation of Earth’s axis of rotation. The shift changes how much summer sun high latitude areas of the Earth receive.

Illustration of Precession (7)

Obliquity has a 41,000-year period, changing the tilt of the Earth’s axis relative to the sun. This change in tilt affects how much sun the poles versus the equator receive during a year.

Illustration of Obliquity (8)

Eccentricity has a 100,000–400,000-year period, changing the shape of the Earth’s orbit around the sun. The change in the orbital shape alters the length of the seasons and, in turn, affects the importance of precession.

Illustration of an exaggerated eccentricity (9)

The interaction of these orbital parameters will not cause a substantial change in the total energy reaching the Earth from the sun over the course of a year. Instead, their interaction causes a difference in the distribution of solar energy across the Earth’s surfaces.

When the Earth’s northern latitudes receive less summer sun, its ice sheets expand, reflecting more sunlight that consequently causes a lowering of temperatures. This driver of additional cooling is also known as ‘positive feedback’.

While the orbital shifts, or Earth’s wobbly effect, are fundamental to an oncoming ice age, CO₂ also plays a significant role. It is not a cause of ice ages but acts as a destabilizing factor and serves as feedback to amplify the changes caused by the orbital variations.

Lower CO₂ and ice ages reinforce each other. A cooling down causes CO₂ to become more soluble in water, allowing water to absorb more CO₂ and reducing it in the atmosphere, thus amplifying a cooling down of the atmosphere. Other factors also play in; orbital shifts that allow ice sheets to grow, causing sea levels to fall dramatically. Growing ice sheets result in the exposure of large landmasses previously underwater, giving way to vegetation that grows and consumes more CO₂. Expanding sea ice also covers up those areas where deep-ocean CO₂ usually comes to the surface, limiting the release of CO₂ from the ocean and into the air.

Homo Sapiens

It appears that the story of CO₂ as feedback to climate change is one of the ancient stories of our Earth. For the last 800.000 years, the air bubbles within the ice cores tell us a story of a relatively predictable and very stable fluctuation between 175 and 300 ppm in correlation with ice ages. These low CO₂ levels occurred alongside the explosive evolution in humankind that in over less than one million years saw our ancestral species spread further throughout the world. Here, they built shelters, picked up spears for hunting, produced complex stone blades, and gave way to our direct ancestors, the Homo Sapiens, some 300.000 years ago.

With the advent of Homo Sapiens came the creation of beaded jewelry, ritual burials of the dead, cave art, and one of the most fundamental leaps to humankind, our transition into agricultural societies, approximately 10,000 years ago.

Humankind had by then been long-time users of fire and tools. They had developed hunting techniques and traps and were communicating through complex speech. Yet, a shift was about to take place that would irreversibly alter the way we humans lived. It was a shift that set our race on a fundamentally different course and changed us from the hunter-gatherers we had been since we first evolved on Earth into farmers.

Again, the lightest pockets of air provide weighty insight into our evolution and its relationship with CO₂. Around the development of agriculture, the Earth had just come out of the last ice age to date. As known from ice core data, this transition meant a rise in CO₂ levels from 189 ppm to 268 ppm, which, in turn, allowed more rapid vegetation growth. While unverified, it is notable that this revolution to our way of life occurred when CO₂ was at the highest since humankind had developed into a cultivated species. One might consider a correlation between the high CO₂ content and the favorable conditions this created for the domestication of plants and farming.

History of fossil fuels

Like the trapped air bubbles that point us towards this possible story, other decisive deposits also lie below the ground. In this case, however, their unearthing first initiated some 6,000 years ago would not document climate change but instead be the driving force behind it.

From the farming revolution, Homo Sapiens moved fast. Within the next 4,000 years, we have evidence of man smelting copper and tin and even producing the first writings.

These writings are attributed to the world’s first civilization in Mesopotamia that developed around 6,000 years ago. Mesopotamia was an ancient region between the Zagros Mountains and the Arabian Plateau, corresponding mainly to today’s Iraq as well as parts of Iran, Syria, and Turkey. Mesopotamia is a place of many firsts and beginnings: Here, on the banks of the Euphrates River, man first encountered a black substance spilling from the ground. He named the place The Fountains of Pitch, and while it may be called a fountain, it is an oil seep. This first use of a substance from ancient times initiated our first engagement with crude oil, more commonly known as petroleum, and marks the beginning of our lasting and impactful relationship with those other energy-rich deposits in the Earth — fossil fuels (10).

For a good reason, many say that the history of fossil fuels is as old as the history of human civilization. However, fossil fuels are, of course, much older than this. They are materials formed from dead organisms that sunk below the surface of the Earth millions of years ago. Once organic material, various geological conditions, such as pressure, temperature, rocks, and sediment, have led to the formation of many different fossil fuels — the three most common being oil, natural gas, and coal.

Humans have used fossil fuels to enhance their way of life since their first encounter with oil at The Fountains of Pitch. The Mesopotamians used the residue from the oil seeps, also known as Bitumen, as mortar for their building structures. In other parts of the world, ancient Egyptians used it to assemble and adhere the bricks making up the pyramids. Coal’s first discovery and mining took place not long after, probably 5,000 years ago in China. Later, around 2,000 years ago, these Chinese civilizations would also capture natural gas and oil in bamboo pipes and transport them into the home for indoor heat and lighting.

Each burning bamboo pipe, each piece of coal, each petroleum lamp emits CO₂. Fossil fuels are aptly names as they form from the fossilized, buried remains of plants and animals that lived millions of years ago.

When these animals and plants died, slow geological processes trapped their carbon and transformed them into natural resources. Fossil fuels, therefore, act as reservoirs that store carbon. When we burn them, we release CO₂, collected over millions of years, into the atmosphere.

Each gas has a lifetime in the atmosphere, ranging from a few years to thousands of years. GWP or Global Warming Potential measures this lifespan and the warming effect a given gas has on the atmosphere. It refers to the total energy that a gas absorbs over a particular period compared to carbon dioxide. Carbon dioxide, CO₂, measured over 100 years, has a GWP of 1 and serves as a baseline for other GWP values. Due to this definition, many people believe that the life of CO₂ in the atmosphere, is 100 years. But CO₂ remains in the atmosphere for much, much longer: Changes in atmospheric CO₂ concentrations persist for thousands of years, as seen from past historic decreases in CO₂ levels.

The early use of fossil fuels was relatively insignificant to the CO₂ content in our atmosphere. The significance of the burgeoning relationship between man and fossil fuels, however, cannot be overestimated. Ice core data tracks a relatively stable range for these 6,000 years, CO₂ levels fluctuating between 260 ppm and 284 ppm, with a slow rise over the whole period because we are still on our way out of the last ice age. In 1850, the CO₂ content again reached 284 ppm, a local maximum. But instead of a gradual and minor decrease in the following period, as data for previous periods would predict, each year from 1850 onwards marks a steady incline that only gathers pace with every decade to follow.

Illustration of CO₂ levels, 14,000 years before present

This increase in atmospheric CO₂ levels correlates with the industrial revolution, one of the most defining shifts in modern history. A shift that transformed agrarian societies in Europe and America into urban, industrialized ones. James Watts’ steam engine, invented in 1776 was an improved version of Thomas Newcomen’s 1712 design. Watts engine was powered by coal instead of wood and drove the industrial revolution. His steam engine transformed manufacturing methods from hand tools driven by human and animal power to coal-powered machinery. Paving the way for mass production — and an explosive increase in coal consumption.

In 1900, CO₂ had risen from 284 ppm to 296 ppm. By then, coal had replaced wood as the primary source for indoor heating, and by 1960 it was the primary energy source in the generation of electricity in the U.S.

The explosive increase in the use of coal coincided with another game-changing invention by German engineer Carl Benz, in 1885 — the internal combustion engine that ran on gasoline. The combustion engine ultimately led to the launch of Henry Ford’s mass-affordable automobile in 1908, which dramatically drove up the gasoline demand. By around 1950, oil had become the most used energy source in the U.S. If we zoom in to that same period, in 1950, data from the ice core drillings now record CO₂ levels at 310 ppm.

From here on, the world’s energy consumption had made itself entirely dependent on fossil fuels. Energy demand increased year by year. During the following 50 years, from 1950 to 2000, an increase in CO₂ from 310 ppm to 370 ppm is recorded. In only 63 years CO₂ has increased with more than 100 ppm, to almost 420 ppm in 2021. 2013 marked the year we first moved above the level of 400 ppm as a civilization.

CO₂ levels during the past 300 years

At the same time as CO₂ levels are rising, the Oxygen content in our atmosphere is decreasing. This decrease is also caused by the burning of fossil fuels. This also shows that our biosphere cannot keep up replenishing the Atmosphere with Oxygen at the speed that we are burning fossil fuels.

Oxygen levels from 1990–2021

Of course, this ancient breathing Earth has been here before. The last time CO₂ levels where above 400 ppm was about 5 million years ago — long before our ancient breathing human ancestors first walked its African soil. CO₂ lowered some 120 ppm over the following 4 million years, possibly creating the exact atmospheric conditions required for human evolution to take place.

Over the following 1 million years, a long and stable period saw us make the explosive and impressive leaps as species, societies, and individuals that have brought us to this point in time. To a point where we have become capable of inventing, sourcing, and burning enough fossil fuels to put back as much CO₂ in the atmosphere over 150 years as it took the Earth 4 million years to remove.

CO₂ levels in the past 800,000 years

We piece this long story of humans, fossil fuels, and atmospheric conditions together from the many sources Earth provides us with: Stromatolites, ice cores, air bubbles, and archeological findings. We came into existence and have evolved as a species in stable conditions that have fluctuated without extremity. How the explosive increase in CO₂ will affect us as a race is unknown to us.

A year before we first pass the 400-ppm threshold, a man falls to Earth. He has returned from the limits of our existence, where the atmospheric composition would mean death were it not from the recognizable spacesuit that protects him. He has made his safe landing. The date is October the 14th, 2012. At the top of Mauna Loa in Hawaii, its observatory has recorded the CO₂ level at 391ppm. Baumgartner, too, has broken records. He removes his helmet to finally breathe in the fresh air that has sustained him and all of humankind to have lived below the azure atmospheric blanket over the last 3.6 million years.


This is the third chapter of my book “Atmosphere, CO₂ on my mind”. You can find more information and references on my website.

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  2. Tobias P.V. (2006). “Homo habilis — A Premature Discovery: Remembered by One of Its Founding Fathers, 42 Years Later”. The First Humans — Origin and Early Evolution of the Genus Homo. Vertebrate Paleobiology and Paleoanthropology. Springer, Dordrecht. pp. 7–15
  3. David A. Raichlen; Adam D. Gordon; William E. H. Harcourt-Smith; Adam D. Foster; Wm. Randall Haas Jr (2010). Rosenberg, Karen (ed.). “Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics”
  4. Herries, Andy I. R.; Martin, Jesse M.; Leece, A. B.; Adams, Justin W.; Boschian, Giovanni; Joannes-Boyau, Renaud; Edwards, Tara R.; Mallett, Tom; Massey, Jason; Murszewski, Ashleigh; Neubauer, Simon (3 April 2020). “Contemporaneity of Australopithecus, Parantrhopus, and early Homo erectus in South Africa”
  6. their-role-in-earths-climate/
  10. Fossil-Fuels.amp.html



Daniel Lux

What scares me about climate change is the effect that high CO2 levels have on our bodies and intelligence, yet very few are writing about this.