We measure our lives in rotations and revolutions. Earth spins through darkness into light every twenty-four hours, giving us the rhythm of waking and sleeping, the pulse of day and night that structures consciousness itself. The planet tilts and orbits, creating summer and winter, the death of leaves and their return. These cycles feel eternal because they repeat within a human lifetime, within memory, within the span of attention that evolution has granted us. But what if these familiar rhythms are merely the frantic heartbeat inside a vaster organism whose breathing we cannot perceive, whose seasons we mistake for eternity?

Our solar system completes one orbit around the Milky Way’s center approximately every 230 million years – a galactic year, a cosmic revolution. Since Earth coalesced from stellar debris 4.6 billion years ago, it has traced this immense circle through space fewer than twenty times. Since the Cambrian explosion birthed complex life in Earth’s oceans 541 million years ago, our planet has circled the galaxy merely 2.3 times. All of recorded human history – every empire risen and fallen, every thought conceived, every love declared – occupies less than one-thousandth of one percent of a single galactic orbit. We are mayflies boasting of our permanence at dawn, certain the sun will never set.

i. Recurring time
The parallel beckons with uncomfortable insistence. As Earth rotates, one hemisphere plunges into night while the other basks in day. As Earth orbits the Sun with its axis tilted, the Northern Hemisphere freezes while the Southern Hemisphere blooms, then reverses. These cycles emerge from geometry and gravity, from the simple fact of motion through space creating differential exposure to energy. Could our solar system’s 230-million-year journey through the galactic spiral arms create analogous variations – not in sunlight, but in cosmic radiation, gravitational perturbations, interstellar medium density, and the frequency of nearby supernovae? The science suggests, tentatively and with significant controversy, that it might. Every 30 to 35 million years, our solar system crosses the galactic plane – the dense disk of stars, gas, and dust that forms the Milky Way’s equatorial region. Studies have identified periodicities in Earth’s extinction events at roughly 26, 30, and 62 million-year intervals, numbers that haunt the fossil record like a hidden metronome.

Some researchers correlate these pulses of death with spiral-arm crossings that occur every 140 to 180 million years, periods when our solar system plunges through regions dense with young massive stars, supernova remnants, and cosmic-ray sources. In these galactic “arms,” cosmic radiation may increase by 50 to 200 percent, bathing planets in energetic particles that cascade through atmospheres, trigger cloud formation, mutate DNA, and maybe tip climatic systems into catastrophic reorganization. Iron meteorites frozen in space for eons record this cosmic breathing. Their exposure to galactic cosmic rays reveals a periodicity of 143 million years, matching theoretical spiral-arm-crossing times with uncanny precision. When scientists examined Earth’s geological record of ice ages, some found the same rhythm – epochs of glaciation separated by roughly 140 million years. Others, using more sophisticated asymmetric models of galactic structure, found these correlations dissolve into statistical noise. The debate remains unresolved, but the possibility hangs luminous in uncertainty: that our planet’s climate, the crucible of all terrestrial evolution, may dance to rhythms played on galactic timescales. What if planets themselves undergo transformations as radical as the shift from summer to winter, changes so profound they would render one season’s inhabitants utterly extinct in the next?

ii. Changing worlds
Mars whispers of such transformations. Four billion years ago, Mars possessed a magnetic field generated by a molten iron core. This invisible shield deflected the solar wind, protecting a thick atmosphere capable of sustaining liquid water across the planet’s surface. Rivers carved valleys through Martian highlands. Minerals formed in standing water. For possibly a billion years, Mars might have cradled microbial life in warm, wet environments. Then the core cooled. The magnetic dynamo stilled. Unprotected, the atmosphere began hemorrhaging into space as solar wind physically knocked atmospheric atoms away – a process called sputtering. Over the next 3.7 billion years, Mars lost approximately 65 percent of its atmosphere. The greenhouse effect collapsed. Surface water froze or evaporated into the thinning atmosphere and was split apart by ultraviolet radiation, with its hydrogen escaping into space forever. The planet that might have been habitable became a frozen desert where liquid water cannot persist. Venus tells the opposite story, a tale of suffocation by abundance. Early Venus, despite its proximity to the Sun, may have harbored liquid water oceans for up to two billion years. But proximity becomes destiny given sufficient time. As the young Sun gradually brightened, Venus absorbed more energy. Ocean water evaporated into the atmosphere. Water vapor, itself a potent greenhouse gas, trapped more heat, leading to further evaporation in a runaway positive feedback loop. Ultraviolet radiation split water molecules into hydrogen and oxygen. Hydrogen, too light to hold, streamed away to space. Without water, carbon dioxide could not be locked into carbonate rocks through weathering. CO₂ accumulated. Temperatures soared. Today, Venus’s surface reaches 462°C under atmospheric pressure ninety times Earth’s – hot enough to melt lead, crushing enough to kill instantly. The planet that might have been Earth’s twin became Hell’s anteroom.

And Earth? Our world too has known radical transformations, episodes when ice sheets extended from the poles to the equator between 900 and 600 million years ago – Snowball Earth events when our planet became a gleaming white sphere barely distinguishable from a frozen moon. Volcanic outgassing eventually pumped enough carbon dioxide into the sealed atmosphere to create a greenhouse effect strong enough to melt the ice, but the transformation took millions of years; eons during which life clung to survival in deep-ocean hydrothermal vents or beneath ice, where volcanic heat could melt narrow refuges. Earth eventually emerged from its frozen state profoundly changed, setting the stage for the Cambrian explosion of complex life. Could planets cycle through habitability? Could Earth become Mars-like while Mars, pushed by some cosmic perturbation into a temporary stable orbit and blessed with renewed volcanic activity, bloom briefly with primitive life? Could Jupiter’s moon Europa, locked in ice today, orbit into warmth during some galactic summer? The mechanisms exist: atmospheric loss through stellar wind stripping, magnetic field variations, changes in cosmic radiation exposure, orbital parameter shifts, runaway greenhouse effects, and the slow brightening of stars as they age. The transformations are not truly cyclical but evolutionary – planets change, often irreversibly, along pathways determined by physics and initial conditions. Mars will not regain its atmosphere without massive intervention. Venus will not cool and rain again. But the metaphor resonates: planets have seasons measured not in months but in hundreds of millions of years, and what thrives in one epoch perishes in the next.

iii. Insects in the cosmic winter
There exists a species of Antarctic midge, Belgica antarctica, that endures the austral winter frozen solid for months. Its cells contain proteins that prevent ice crystals from rupturing cell membranes. When spring returns, the midge thaws and resumes its brief life. An observer existing only during winter might conclude that life on Earth is impossible, never suspecting that the frozen corpses scattered across the ice would rise again. Are we such midges on a galactic scale? Earth’s current Cenozoic climate – relatively warm, stable, conducive to complex land life and technological civilization – may be merely one summer in an immense year. The conditions that permitted humanity to emerge and develop agriculture, cities, science, and philosophy have existed for possibly 12,000 years, one sixty-millionth of Earth’s history. Homo sapiens has existed for roughly 300,000 years, one fifteen-thousandth of Earth’s age. Our entire biological lineage since the last major extinction event 66 million years ago represents less than 30 percent of one galactic orbit. The fossil record stretches back 3.5 billion years, yet it remains maddeningly incomplete. Fossilization requires extraordinary circumstances – rapid burial in fine sediment, anaerobic conditions to prevent decay, and subsequent protection from heat, pressure, and erosion. Less than 0.1 percent of organisms that have ever lived became fossils. The further back we look, the sparser the record becomes as geological processes destroy evidence. Oceanic crust, which covers 71 percent of Earth’s surface, recycles completely every 100 to 200 million years through subduction into the mantle, where it melts and reforms.

Continental crust, though more stable, endures constant reshaping through erosion, mountain building, glaciation, and metamorphism. In 2018, NASA climate scientist Gavin Schmidt and astrophysicist Adam Frank posed a question they called the Silurian Hypothesis, named after Doctor Who’s fictional ancient reptilian civilization: If an industrial civilization existed on Earth tens or hundreds of millions of years ago, could we detect it today? Their answer proved unsettling. After roughly 100 million years, almost no direct evidence would remain. Cities would erode to dust. Metal artifacts would rust and disperse. Plastics might persist in certain sediment layers, but distinguishing ancient plastics from natural organic compounds in metamorphosed rock would be nearly impossible. Even dramatic signatures like elevated carbon dioxide, ocean acidification, mass extinction pulses, and unusual isotope ratios in sediment layers would resemble natural catastrophes – massive volcanic eruptions, asteroid impacts, or climate shifts. The Anthropocene will leave markers: a thin layer enriched in heavy metals, synthetic radioactive isotopes, and carbon-isotope ratios betraying fossil-fuel combustion. But compressed in geological strata and examined 200 million years hence, this signature would appear as a narrow anomalous band, a geological instant, easily attributed to volcanism or impact events. The 66-million-year-old Cretaceous-Paleogene boundary that marks the asteroid impact killing the dinosaurs appears in many locations as a layer less than an inch thick. Sixty-six million years have not yet erased that signature, but another galactic half-rotation might.

iv. Silence beneath the stones
This raises a possibility that should disturb any thoughtful consideration of human uniqueness: We might not be Earth’s first technological civilization. Previous rises and falls could lie buried beneath geological time, erased by the planet’s own metabolism. The Permian-Triassic extinction 252 million years ago killed 90 to 96 percent of marine species and 70 percent of terrestrial vertebrates – the worst catastrophe in the fossil record – and took 10 million years for ecosystems to recover. Could some disaster of that magnitude have been precipitated not by volcanism alone but by an industrial civilization’s collapse? The geological evidence would look identical. The Cambrian explosion 541 million years ago – when complex multicellular life suddenly diversified into most modern phyla within a geological instant of about 20 million years – represents 2.3 galactic years ago. The Great Oxygenation Event, 2.4 billion years ago, when photosynthetic organisms first pumped oxygen into the atmosphere and poisoned themselves until life adapted, occurred 10 galactic years ago. Each galactic orbit potentially represents a cosmic season with its own dominant life forms, climatic regime, and maybe even intelligent species that rise, flourish briefly, and vanish before the next cycle’s summer.

The concept challenges every narrative of progress and permanence. We imagine humanity’s arc bending toward the stars, toward post-biological existence, toward engineered immortality. But the universe may operate on a different temporal logic. Species exist, civilizations emerge, and then the planet’s surface recycles. The ocean floor slides into subduction zones. Mountains rise and erode. Continents drift and collide. Within 10 million years, cities become unrecognizable mineral deposits. Within 100 million years, they become geological strata indistinguishable from any other sedimentary rock. Earth is not a stable stage upon which the drama of life unfolds; it is an active participant, constantly rebuilding itself, erasing the script as it goes. Claims of ancient artifacts – “out-of-place” objects supposedly showing advanced technology in impossible contexts – have been thoroughly debunked by archaeology and geology. The London Hammer embedded in “ancient” rock formed rapidly in mineral-rich water around a 20th-century tool. Crystal skulls supposedly from pre-Columbian civilizations bear tool marks from 19th-century European rotary saws. The Dendera temple carvings, which are allegedly depicted with electric lights, clearly illustrate Egyptian creation mythology involving lotus flowers. Every supposed anomaly dissolves under scrutiny into a hoax, misidentification, or misunderstanding of geological processes.

Yet the debunking of specific claims does not diminish the deeper question. Absence of evidence is not evidence of absence, especially when the timescales involved ensure that evidence is destroyed. If a Devonian civilization thrived 375 million years ago and collapsed in the extinction event that marked the end of that era, what would remain? If a Permian technological species engineered its own demise 250 million years ago, how would we distinguish its industrial collapse from the massive Siberian volcanic eruptions that also occurred then? The answer might be: we couldn’t, not with certainty, not after that much time.

v. Vertigo of deep time
What does it mean for human significance if we are merely the latest iteration in an endless cycle? If intelligence is not a unique emergence but a recurring phenomenon, appearing whenever planetary conditions permit and vanishing when they change? The question intersects with every philosophical conception of meaning and purpose. Western thought has largely embraced linear time – creation, history, progress, culmination. The Judeo-Christian tradition posits a beginning (Genesis), a directional narrative (salvation history), and an end (Apocalypse). The Enlightenment secularized this into progressive evolution: from ignorance to knowledge, barbarism to civilization, Earth-bound to cosmic. Even our extinction anxieties preserve this linearity; we fear being the final chapter, the species that either succeeds in reaching the stars or fails and ends the story. Eastern philosophies offer different temporal architectures. Hindu cosmology conceives of vast cycles – the universe breathed out by Brahma, existing for 311 trillion years, then absorbed back, only to be created anew. Buddhist thought emphasizes impermanence and cyclical rebirth at both cosmic and individual scales. Time is not a river flowing toward an ocean but a wheel turning endlessly, with beings ascending and descending through states of existence.

Indigenous cosmologies often incorporate cyclical time as well – the Hopi describe multiple previous worlds destroyed by fire, flood, and upheaval before the present fourth world. Mayan Long Count calendars measured vast epochs, though popularizers misunderstood them as predictions of apocalypse rather than as the simple turning of cosmic wheels. The Stoics of ancient Greece and Rome conceived of eternal recurrence, in which the universe periodically returns to identical states and history repeats itself infinitely. If cosmic seasons are real in any meaningful sense, these cyclical philosophies might come closer to the truth than linear narratives. Humanity would not be climbing toward some transcendent future but flowering briefly in conditions temporarily favorable to our form of intelligence. Our achievements – art, science, love, the cathedrals of culture – would be no less beautiful or meaningful for their impermanence, but neither would they be unique. Other minds in other epochs might have gazed at these same stars and asked these same questions, then vanished so completely that we cannot detect even the faintest echo of their wondering.

vi. First ones
There persists a nearly irresistible tendency to believe ourselves exceptional – the first to achieve consciousness, the first to create language, the first to contemplate the cosmos. This belief requires ignoring vast spans of time and evidence of intelligence in other species. Crows solve multi-step problems. Octopuses demonstrate remarkable learning despite evolving intelligence independently from vertebrates. Elephants mourn their dead. Dolphins have regional dialects and may possess names for individuals. We are certainly the first technological civilization on Earth that we know of, but that knowledge extends with confidence only a few million years into the past for terrestrial complex life and becomes increasingly speculative beyond 100 million years. The Silurian Hypothesis implies a troubling possibility: industrial civilizations might be common in planetary history yet almost always undetectable after sufficient time. If civilization typically lasts 10,000 to 1 million years – long enough to develop technology but short relative to geological time – and if planetary conditions favor such emergence every 100 to 500 million years, Earth could have hosted multiple previous technological species. Each would consider itself the first, the pinnacle, the ultimate purpose of evolution. Each would be wrong.

This is not to claim previous civilizations existed – the evidence remains absent, and extraordinary claims require extraordinary evidence. But the absence of evidence, given the timescales and processes involved, tells us almost nothing. It is a silence that neither confirms nor denies, a blank page where anything or nothing might be written. The responsible position is uncertainty, not confidence. Consider the implications for meaning. If consciousness arises, flourishes, builds, discovers, loves, and then is erased utterly without a trace, what anchors value? Religious frameworks offer transcendence – an eternal soul, a cosmic judge, an afterlife where accounts are settled and nothing is truly lost. Secular frameworks typically appeal to legacy – the works we leave, the knowledge we accumulate, the future we shape for descendants. But if geological time erases legacy and descendants might themselves be erased, these anchors slip.

vii. Cosmic yawn
Perhaps meaning must be found elsewhere – not in permanence but in the quality of experience itself. The joy of understanding, even briefly, how galaxies spiral and planets form. The love between individuals, intense and honest, even if it spans only decades before both lovers and all memory of them vanish. The beauty of a sunset, which exists entirely in the moment of perception, regardless of whether that moment will be remembered. This is the existential response: creating meaning despite – or, one might imagine, because of – its impermanence.

The universe appears indifferent to our survival. The Sun will brighten as it ages, increasing luminosity by approximately 10 percent every billion years. In roughly 1 to 2 billion years, Earth will enter a runaway greenhouse effect. Ocean water will evaporate into the atmosphere faster than it can rain back down. Water vapor, a potent greenhouse gas, will trap more heat, causing more evaporation in an accelerating feedback loop. Ultraviolet radiation will split water molecules apart. Hydrogen will escape to space. Earth will become Venus, a scorched hellworld with surface temperatures exceeding 400°C. Long before that, in about 600 million to 1 billion years, atmospheric carbon dioxide will drop below levels required for plant photosynthesis, causing a mass extinction that destroys most complex life.

These futures are not speculative; they are consequences of well-understood physics. Earth’s remaining habitability represents roughly one more galactic summer. Then autumn descends, and after that, a winter from which no thaw will come. Any civilizations that arise on Earth after ours will face the same ultimate deadline, the same implacable ticking toward uninhabitability. Mars already endures its permanent winter. Venus boiled in its permanent summer. Earth stands poised between, temporarily blessed, counting down.

viii. Are cosmic seasons real?
So we return to the question: are cosmic seasons real? The answer may be both yes and no, depending on how we approach the question.

Yes, in that galactic dynamics create variations in cosmic radiation, supernovae proximity, interstellar medium density, and gravitational perturbations on timescales of tens to hundreds of millions of years. Our solar system’s orbit through the galaxy exposes Earth to varying environmental conditions, potentially correlating with extinction events and climate changes. However, the strength of these correlations remains vigorously debated in scientific literature.

Yes, in that planets themselves undergo profound transformations – Mars from wet to dry, Venus from potentially habitable to an inferno, Earth through multiple Snowball episodes. These changes have timescales vastly longer than human seasons but vastly shorter than the universe’s age.

No, in that these transformations are not truly cyclical. Planets evolve irreversibly. Mars will not regain its atmosphere through natural processes. Venus will not cool and rain. When Earth boils a billion years hence, it will not later freeze and restore itself. These are one-way journeys through state space, not returns to previous conditions.

No, in that the galactic “seasons” operate through mechanisms entirely different from planetary seasons – not variations in stellar distance and axial tilt but changes in radiation environment, stellar encounters, and cosmic ray exposure. The metaphor illuminates but also obscures.

Yet metaphors shape understanding. To conceive of humanity as brief mayflies of a galactic season shifts perspective. We are not the culmination of 13.8 billion years of cosmic evolution building toward some purpose. We are opportunistic life, flourishing when conditions permit, facing extinction when they change. This is humbling, even crushing to narratives of human exceptionalism. But there is also a strange liberation in it. If we are temporary, then the universe does not depend on us or need us to fulfill some cosmic destiny. We are free to simply exist, to experience, to understand what we can while we can. The fact that our achievements will erode to nothing does not render them valueless any more than the certainty of individual death renders individual lives meaningless. We create, love, and discover because doing so enriches the texture of consciousness in the present, not to build monuments lasting eternally.

ix. Galactic flowers
In the dense cores of long-dead stars, hydrogen fused into helium, helium into carbon, carbon into oxygen, neon, silicon, and iron. When those massive stars exploded as supernovae, they forged heavier elements – gold, uranium, plutonium – and scattered them into interstellar space. Those elements condensed into new stellar nebulae. One such cloud collapsed 4.6 billion years ago, forming our Sun and planets. The iron in our blood, the calcium in our bones, and the oxygen we breathe were all created in stellar furnaces and supernova forges. We are not in the universe; we are of the universe, patterns of organization that atoms occasionally form when conditions permit. Those conditions are temporary. Earth has known approximately 15 galactic seasons since life emerged. In each season, life adapted to prevailing conditions – thermophiles thriving in Archaean heat, photosynthesizers transforming the atmosphere in the Proterozoic, complex organisms exploding in the Cambrian, dinosaurs dominating the Mesozoic, mammals ascending in the Cenozoic. Each age believed itself to be permanent. Each ended.

We stand in a brief warm spell between ice ages, in a moment of atmospheric stability between extinction pulses, on a planet whose remaining habitability can be measured in fractions of galactic orbits. To recognize this is not to despair but to see clearly. We are blossoms on a tree that will itself one day burn, growing in soil made from the decay of previous forests, under a sun that will eventually swell and consume us. The blossoms are no less beautiful for their impermanence. Indeed, one might imagine they are more beautiful because they are impossible to preserve. The question the cosmos poses is not “Are you eternal?” but “What will you do with your season?” Will we spend our time insisting we are the center of creation, the purpose of existence, the first and only consciousness to matter? Or will we accept our place in the great wheel – another flowering, another brief arrangement of atoms complicated enough to wonder at itself, destined to disperse when conditions change?

There is grandeur in this view. Life has persisted through approximately twenty galactic orbits, four billion years, surviving snowball freezes, asteroid impacts, megavolcanic eruptions, oxygen poisoning, and multiple mass extinctions. It has taken myriad forms, most lost to time, some preserved briefly in stone. Intelligence has emerged at least once and possibly more times that we cannot detect. The pattern suggests resilience, creativity, and an almost inexhaustible capacity for adaptation and reinvention. We may not be the first intelligence Earth has hosted, and if life persists for another few hundred million years, we will likely not be the last. Future archaeologists – whether human descendants or entirely different species – will not find our cities, will not read our books, will not know our names. But they might, if they develop sufficient technology, detect a slight anomaly in sedimentary rocks from the late Anthropocene – elevated levels of heavy metals, unusual carbon isotope ratios, traces of synthetic compounds. They might reconstruct from this thin band that some form of complex civilization briefly flourished here, then vanished, leaving almost nothing behind.

And perhaps they will understand what we are only beginning to grasp: that consciousness is not a ladder to climb but a wheel that turns, each spoke a different form, each rotation a new experiment in what complexity can achieve. Some species last millions of years in stable ecological niches. Others burn bright and brief, transforming their world before vanishing. Neither strategy is superior. Both are ways of being, temporary solutions to the temporary problem of existence. The cosmic seasons turn. Ice ages come and go. Spiral arms cross our path. Extinction pulses rhythm through deep time. And in the brief spaces between catastrophes, in the fleeting warm seasons when conditions align, planets bloom with life. We are that blooming, now, in this moment, neither first nor last but current. The flower does not mourn that it will fade. It opens to the sun, fulfills its nature, and in doing so, participates in patterns vaster than itself. This is our season. This is our orbit. We inherited a world shaped by four billion years of prior evolution, 20 galactic revolutions of stellar alchemy, extinction, survival, and adaptation. We will bequeath it, changed by our presence, to whatever comes next. The wheel turns. The seasons change. And for this brief cosmic spring, we are here, awake, aware, able to contemplate the immensity that contains us. It is enough.

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Notable Credits:
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