The story of life on Earth is fundamentally a story of energy. Ever since chemistry became biology by innovating a way of capturing energy, its evolution has been driven by finding new ways of harnessing and using this elixir. But this planetary-scale development heralds a remarkable new role for life and its relationship with energy. It also raises new questions over responsibility and obligation. We could become the first species to intentionally support and even restore the livability of the biosphere for ourselves and our coevolved species. Or we could, through our success, deliver a mass extinction, including paradoxically of ourselves.

So how did we get to the point where a single species is able to change the energy balance of a planet in a blink of geologic time?

The Engine of Life

Let’s start with the third-closest rock orbiting a star. Earth’s extraordinary nature arises from its size, position and distance from the sun, as well as its geology — the plate tectonics that belch forth chemicals — and its atmosphere, which retains and cycles that chemistry. Uniquely, as far as we know, geology helped produce biology some 4 billion years ago at deep-ocean geothermal vents, where energetic chemistry likely generated an alchemy of self-replicating, energy-harnessing molecular systems: life. The biosphere emerged as a product of the geosphere, which, in turn, creates new geologies. Lichens digest solid rock into soils; rivers run through channels eroded by tree roots; coral polyps collectively construct limestone and form atolls.

Life has geologic force because of its use of energy, the currency that connects everything in the universe and drives every physical, chemical and biological reaction. Its flow passes through every living cell in a multitude of exchanges that originate with nuclear reactions in the sun.

For any living system, energy is the main constraint on abundance and productivity. Life spends energy to reduce entropy — a measure of disorder — by ordering random atoms into organized structures: A sequence of DNA is arguably the ultimate rejection of entropy. Of course, whenever energy is expended to reduce entropy, this local effect is outweighed by an increase in the total entropy of the universe. The creation of order must also create disorder, in the form of heat.

Over billions of years, life evolved and organisms optimized different ways of harnessing various forms of energy. These energetic innovations affected the environment, sometimes dramatically. When cyanobacteria developed chlorophyll-based photosynthesis some 2.4 billion years ago, its ability to harness sunlight and carbon dioxide to create organic fuel led to a tremendous elevation of oxygen levels in the atmosphere. Oxygen displaced the greenhouse gas methane and caused global cooling, with ice sheets extending from the poles to the tropics. The oxygenation also led to the formation of an ozone layer in the upper atmosphere that absorbs most of the sun’s ultraviolet rays, setting up conditions for life to colonize land.

As life diversified and evolved greater complexity, its thermal influence grew. The reactions that occur in organisms change the atmospheric concentrations of gases, including water vapor, carbon dioxide and methane. Those gases trap heat, making our planet around 30 degrees Celsius (86 degrees Fahrenheit) hotter than it would be without the biosphere’s greenhouse effect.

The biosphere consists of intricate, interdependent relationships that living beings create with one another, with their physical environments, and with Earth systems. Characterized by the flux and flow of energy, matter, charge and influence, the biosphere is an engine of life that extends from the deep oceans into the atmosphere.

Since all life is limited by its need for energy, the quest for energy shapes every being, from the tiniest cell to the most complex society, and drives the evolutionary process. But when our human ancestors began burning the planet’s biomatter, everything changed.

Becoming Human

Around a million years ago, at the very beginning of the biggest disruption to life’s energetic capabilities since the emergence of cyanobacteria, humans learned to harness a new kind of energy source: combustion. While other animals are limited by the metabolic energy they can harvest biologically, fire — an explosion of energy released as fuel reacts with oxygen — gave our ancestors an external energy source that was orders of magnitude more powerful.

Our ancestors cooked food, using fire as a form of digestion to assist the work of teeth, jaws and guts on tough, raw foods. Fire kept our ancestors warm without fur, scared off predators and cleared landscapes for hunting. One evolutionary response to this extracorporeal bounty of energy was a growth in brain size and specialization, including the development of a bigger prefrontal cortex. As a consequence, humans are smart, cooperative and exceptionally social. Those traits made us capable of a remarkable phase change in evolution.

Just as genetic information is passed down through generations of families, humans pass a whole suite of cultural information, including knowledge, behaviors, technologies, language and values, through societies and across generations. By learning from each other, teaching each other and relying on each other for resources, humans created complex and diverse cultures that produced increasingly effective solutions to life’s challenges.

Human cultural evolution allows us to adapt to new environments and conditions far faster than our genes ever could. Our societies of cooperating, interconnected individuals improve group and individual survival and enjoy great scope and efficiencies in the way they harvest energy and resources.

It is this collective culture, more than any individual intelligence, that defines Homo sapiens: a species not simply the product of its biosphere, but an agent of its transformation. We don’t have an ecological niche because we don’t need one; we can alter any environment to suit us. In this way, humanity has become the most populous big animal on Earth and has an outsize effect on the planet, changing its ecologies, landscapes and energy regime.

This shift didn’t happen immediately. It took hundreds of thousands of years for cultural complexity to deliver the technologies and social institutions we have today. For 95% of that time, humans were constrained by the trenchant ice ages of the Pleistocene. Then, around 11,000 years ago, Earth entered the stable, mild climate of the Holocene Epoch, with higher concentrations of atmospheric carbon dioxide than in the prior tens of thousands of years. Seed-bearing grasses flourished as the ice retreated, and humans responded by evolving farming cultures with much more efficient and expansive harnessing of food energy. The increase in energy and resources propelled the growth of our ancestors’ populations and trade networks, accelerating our cultural diversity and complexity with the development of transportation, cities and industry.

Over the past few thousand years, humans have concocted ways to harvest ever more energy, whether from food production or from different sources of mechanical, chemical or electrical energy. The power of humans, beasts, wind, water, wood and more transformed our environment. The aim was often to improve human lives — at least some human lives. Many of these energy systems had large impacts, but they remained mostly local, the widespread extinction of large fauna notwithstanding.

Then, in the 18th century, humans began using industrial quantities of the densely concentrated energy stored in fossil fuels, releasing organic carbon that had been locked away for millions of years. As the use of fossil fuels began to rise, the gases they produced accumulated in the atmosphere. Initially, the environmental impacts of this Industrial Revolution were, like the prior effects of human energy use, largely local: poisoned waterways and smog-filled urban areas. But that changed as humanity’s vast energetic capabilities expanded. It wasn’t just that the local impacts grew larger — the economy grew on the back of this new energy abundance and living standards improved. A truly global, distributed impact of our hunger for energy emerged.

The Extended Biosphere

No period in our history compares to the Great Acceleration that followed World War II, an explosion in globalized human activity driven by population expansion, innovations in technology and communications, and advances in agriculture and medicine. The Great Acceleration is reflected in the rise in atmospheric carbon dioxide, water use, manufacturing production, ozone depletion, deforestation, pollution and global GDP, which brought welcome increases in lifespan and living conditions for billions of people. Never before had our reach been truly planetary, extending far beyond local or even regional environments to dominate the entire biosphere of Earth.

We have used the biosphere as an infinitely large repository for extraction of resources and deposition of waste. In this way, we are similar to other species: We harvest resources, process them biochemically and expel the by-products. There are two primary differences. Our access to energy amplifies the scale and speed of what we do. And importantly, we are now cognizant of the planetary transformation we have initiated.

Over the past few decades, advances in Earth-system monitoring and modeling mean we understand this impact and the ways in which it threatens our survival. For more than a year, the average temperature of the planet has been more than 1.5 degrees Celsius hotter than the preindustrial average because of our activities, and it is having a noticeable impact on our lives. While it is true that no one decided to heat the planet — there was no purpose beyond the universal and innate biological drive to harness energy — the changes we make to the biosphere are now made knowingly, and thus purposefully.

This makes us something very different from the cyanobacteria that once remade the biosphere. We are planetary actors with purpose. That means we must bear responsibility. Thrillingly, it also means we have the potential to effect positive change.

The biosphere will reach a new equilibrium in the fullness of time, albeit with some extinctions, regardless of how radically we alter it. But what of us? If we and our coevolved species are to survive, then our culture will have to take another extraordinary evolutionary leap. First evolution was driven by individual survival, and then group survival emerged as a viable strategy. Now will we be able to adapt for global biosphere survival? To do so, our species will have to accept its steering role. Just as tools can be seen as extensions of our physiology, a purposefully modulated biosphere — what I call the “extended biosphere” — is now an extension of our species, too.

The extended biosphere is manifest in the intentional modifications we make to its most influential organism — ourselves, from our industrial activities to our cultural preferences — and in the adaptive responses the biosphere makes to us. It can be seen as we switch from harvesting the dense energy source of combustion fuels to using low-density sources, such as photovoltaics. The extended biosphere can be seen in our extraterrestrial activities, which effectively stretch the biosphere beyond the planet. It can be seen in our rewilding of landscapes and in the development of technology to remove carbon dioxide from the atmosphere. It can be seen in humanity’s grand cooperative projects, such as the efforts by various countries to address atmospheric ozone depletion despite the short-term costs, to ban whaling across most of the world, and to declare large parts of the world’s oceans as marine protected areas — protected from us, that is. It can be seen in our emergent human population control, with people around the world deciding to have fewer children despite plentiful resources.

We may not stop there. Our potential to secure the livability of our biosphere could see us geoengineer our oceans, glaciers and atmosphere to restore the Earth’s energy balance.

Energy brought us to this point of peril, and it is the key to our possible salvation. We, the species whose evolution and planetary dominance has been built on hundreds of thousands of years of combustion, are poised to change. We’re switching from burning the sun’s energy in the biologically stored form of wood, gas, peat, oil and coal to capturing it directly. As our energy systems electrify, we will enter an uncharted, post-combustion era. The task is to undertake this species-wide energy transformation at a rate commensurate with our cultural survival — before the planet’s energy balance tips catastrophically against us — and it is fantastically complex, calling for both technological and social solutions.

Humanity’s understanding of itself and this moment will need to evolve to recognize the interconnectedness of human and Earth systems. It means acknowledging that operating in the biosphere as a global species entails considerable adaptation, including adaptation of our energy sources, food systems and waste management. These all require systemic change, but they are well within our capabilities. It is such an awesome responsibility for humanity to take on — and also an opportunity to find purpose and meaning beyond ourselves for the short time the biosphere is ours.