Becoming Earth: How Our Planet Came to Life

Overview

Jabr surveys the many ways in which living organisms, from deep-crust microbes to megafauna to cyanobacteria, have actively shaped Earth’s geology, soil, oceans, and atmosphere over billions of years. The framing argument is that life and planet have coevolved so deeply that, depending on one’s definition of “life,” Earth itself may qualify as alive: a self-sustaining system resisting entropy and maintaining conditions broadly hospitable to life at geological timescales. The book moves through subterranean biology, soil science, oceanography, and atmospheric chemistry, accumulating evidence that the biosphere is not a passenger on a geological conveyor belt but a co-author of the planet’s physical state.

Key Concepts

What Does It Mean for Earth to Be “Alive”?

• A working definition: Jabr opens with the proposition that if “being alive” means being a self-sustaining system that resists entropy, then Earth qualifies, its living components cycle nutrients, regulate atmospheric chemistry, and maintain conditions that allow more life. Whether this definition is useful is a separate question.
• Homeostasis at scale: Just as individual organisms maintain internal homeostasis while themselves hosting ecosystems of microbes, it is plausible that larger systems, coral reefs, old-growth forests, the biosphere as a whole, exhibit analogous self-stabilising feedback. The book returns to this idea throughout without fully resolving it.

Life in the Deep Earth

• Subterranean microbes: Before the 1980s, life below the surface was documented only sporadically. Sustained scientific effort since then has found microbial communities in deep continental crust, subseafloor sediments, and Antarctic ice, environments far removed from sunlight. These communities are powered by radiation and the chemical energy released by its byproducts (e.g., hydrogen from radiolytic splitting of water).
• Metal deposit formation: Microbes contribute to ore formation in two ways: by freeing metals while enzymatically breaking down host rock, and by releasing metabolic byproducts that bind with soluble metals in solution to precipitate new solid mineral compounds.
• Continental crust and granite: By breaking down oceanic basalt and depositing sediment on the ocean floor, microbes may have played a significant role in the formation of granite and thus the continental plates. Sediment loading increases the rate of oceanic plate subduction; in subduction zones, silica-rich rock melts preferentially, rises as magma, cools slowly, and crystallises into granite, the buoyant rock that rafts the continents.

Animals as Geological Forces

• Disproportionate geological influence: Animals comprise the smallest fraction of the biosphere by mass, yet their influence on geology and biogeochemistry is outsized. Examples range from beavers engineering hydrology and earthworms restructuring soil, to the wolf–elk–vegetation cascade in Yellowstone, to the human hunting of Pleistocene megafauna that had maintained the grassy steppe-tundra of Siberia and North America, grasslands whose loss accelerates permafrost thaw and carbon release.
• Cambrian substrate revolution: The appearance of burrowing animals in the Cambrian fundamentally restructured ocean-floor sediment, transforming a previously laminated microbial mat world into a bioturbated, oxygenated substrate, a geological transition driven entirely by biological behaviour.
• Agriculture: The mechanical plow drastically altered soil structure in ways that millennia of biological succession had built up. Synthetic fertilisers and pesticides added further, indirect disruption to soil microbial communities and nutrient cycling.

Soil as a Living System

• Composition: Soil is classified by particle size, from gravel, through sand and silt, down to clay. The ratio of these fractions determines drainage, aeration, and nutrient-holding capacity.
• Life’s role in soil formation: Soil is not merely a substrate on which life happens; life is a primary agent in its creation. Microbes, fungi, plant roots, and animals participate in a coevolutionary feedback, breaking down rock, building organic matter, and adjusting the physical and chemical environment in ways that then select for the organisms best adapted to those conditions.
• Carbon and climate implications: Soil contains more carbon than the atmosphere and terrestrial vegetation combined. How soil life is managed, or disrupted, has direct consequences for agriculture, biodiversity, and the global carbon cycle.

Oceans, Plankton, and Planetary Chemistry

• Redfield ratio and chemical homeostasis: The ratio of carbon, nitrogen, and phosphorus in marine microorganisms (roughly 106:16:1, Redfield’s ratio) closely mirrors that of the open ocean. Phytoplankton and zooplankton are a central mechanism of oceanic chemical homeostasis, drawing down nutrients and releasing them through death and decomposition in patterns that shape seawater chemistry globally.
• The ocean’s carbon thermostat: Photosynthesising marine plankton fix atmospheric CO₂ at a scale comparable to terrestrial vegetation. When they die and sink, some of that carbon is sequestered in deep water or seafloor sediment, the “biological pump.” This makes plankton a major component of Earth’s carbon cycle and, at geological timescales, a significant influence on climate.
• Plankton forming rock: Dead plankton accumulate on the ocean floor and over millions of years are compressed into limestone and chalk. That rock can be recycled through subduction, contribute to mountain-building as tectonic plates collide, weather back into mineral ions, or, as Saharan dust, blow across oceans to fertilise distant terrestrial ecosystems.
• Kelp forests: Marine macroalgae photosynthesize at significant scale, absorb wave energy and dampen coastal storm impact, and underpin entire food webs. Their decline removes a structural element from coastal ecosystems as well as from the local carbon cycle.
• Plastic in geological cycles: Plastics are now accumulating in marine sediments and marine organisms, becoming embedded in geological processes. Life will likely adapt over evolutionary timescales, but not within any human-relevant timeframe.

Atmosphere, Oxygen, and Fire

• Ice-nucleating microbes: Proteins on the outer membranes of certain bacteria (notably Pseudomonas syringae) can catalyse ice formation at temperatures close to 0°C. When these microbes are lofted into the atmosphere, they may seed ice crystals in clouds, potentially increasing the frequency of precipitation, a subtle biological influence on the water cycle.
• The Great Oxidation Event and land plants: Cyanobacteria initiated the GOE (~2.4 Ga) by producing oxygen as a metabolic byproduct, eventually poisoning much of the existing anaerobic biosphere and transforming atmospheric chemistry irreversibly. Land plants completed the rise to modern oxygen levels (~21%), and also intensified the hydrological cycle, increasing evapotranspiration, rainfall, and the rate of rock weathering.
• Oxygen and fire as a feedback: Below ~16% atmospheric oxygen, fires cannot sustain themselves; above ~23%, they become nearly uncontrollable. The current 21% sits in a narrow window, though whether this is a dynamically maintained equilibrium or a coincidence remains an open question.
• Fire ecology and indigenous stewardship: Prescribed burns reduce fuel loads and prevent larger, more destructive fires. Many plant species have evolved traits adapted to periodic fire, serotinous cones, fire-triggered germination, thick bark, evidence that fire has been a recurring ecological force, and that its deliberate management is not new.

Personal Reflection

The book is strongest as a collection of fascinating mechanisms, deep-earth microbes, plankton forming limestone, ice-nucleating bacteria, but its framing I like less. The opening definition of life (a self-sustaining system resisting entropy) is deliberately broad, and Jabr never fully justifies why it is the right one. It feels like the conclusion is chosen first. Whether calling Earth “alive” under this definition adds explanatory power, rather than just rhetorical warmth, is left unexamined.

The same teleological tension runs through the points on regulation. When scientists say plankton “regulate” ocean chemistry or that the biosphere “stabilises” climate, they usually mean something precise: negative feedback loops dampen perturbations within a range. Jabr sometimes lets that slide into a more loaded claim, that life tends toward balance, or that ecosystems are for maintaining conditions. Life created an environment it then simply coevolved with. For instance, the GOE was catastrophic for most life that existed at the time. Whatever organisms survive the current extinction will, in millions of years, have “benefited” from it. The language of purpose of regulation, used this way, imports moral direction that I simply do not agree with.

Related Books

• Entangled Life - Sheldrake explores fungi as another hidden driver of Earth’s chemistry and soil formation, a close complement to Jabr’s subterranean microbes
• The Blue Machine - Czerski covers ocean physics and chemistry in depth, including the biological pump and plankton’s role in ocean carbon cycling
• A Brief History of Earth - Knoll’s deep-time narrative provides the geological backbone that contextualises Jabr’s biological actors

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Parent: Books