Earth’s Memory, Part One

Abstract

Every rock carries a fragment of Earth’s memory. Collectively, these fragments preserve an extraordinary geological record spanning more than 4.5 billion years of planetary evolution. This article traces that record through the deep-time history of our planet—from the formation of Earth’s earliest crust and the Great Oxidation Event, when microbial life transformed the planet’s atmosphere, to the five great mass extinctions that repeatedly reset the trajectory of life, and the Snowball Earth episodes, when our planet experienced its most extreme glaciation. Drawing on more than two decades of fieldwork across Himalaya and Peninsular India, among ancient rocks, minerals, and fossils that bear direct witness to these planetary transformations, it explores how geologists reconstruct Earth’s early history from evidence preserved in the geological archives. Taken together, these geological events reveal a recurring pattern: Earth is a dynamic system in which every major crisis has also created the conditions for new and often more complex forms of life to evolve. That pattern, written into rocks billions of years old, continues to shape the planet today.   

I first learned to listen to rocks long before I had the words to describe what that meant. 

It began in the Himalaya, the youngest mountain range on Earth, still rising, still deforming, and still recording the ongoing collision between continents. During my early fieldwork, I spent long days mapping folded strata, tracing fault scarps, and trying to understand how landscapes preserve evidence of processes operating across vastly different geological timescales. At that time, I often felt that the mountains were trying to say something in a language I had not yet learned. Over time, through fieldwork, mapping, and countless hours spent among rocks and sediments, I began to decipher that silent language. 

The lesson deepened across many other landscapes of India. One of them was Gandikota in Andhra Pradesh, where the rocks are more than one and a half billion years old. Sitting atop the quartzite and sandstone cliffs carved by the Pennar River, compass in hand, I realized I was not merely looking at a spectacular landscape. I was looking at evidence of a world that existed nearly a billion years before complex life emerged, a record of vanished seas and deep time inscribed in rocks (Figure 1). 

Field geology is often described as the science of observing rocks, but it is equally the science of interpretation. From rising mountain ranges to the depth of the oceans, Earth’s landscapes uphold a remarkable archive of past environments and geological events. From the slow movement of continents and the transformation of our atmosphere to the enduring rhythm of climate shifts and resilience of life itself, every profound change leaves a lasting imprint upon the landscape. The challenge and the reward are learning how to recognize those traces and assemble them into a coherent narrative of Earth’s history. 

Four Billion Years in a Sentence

During the early years of my research career, while mapping geological sequences in the high-altitude valleys of Zanskar in the Himalaya, more than 4,500 meters above sea level, I split open a dark grey limestone and found the coiled shell of a Triassic ammonite curled inside. It had lived in the warm waters of the Tethys Ocean more than 200 million years ago, long before humans existed, before the Himalaya had risen, and before the Indian Plate had collided with the Eurasian plates. My fingers, numb with cold, traced the spiral of its chamber. This fossil had not been born at 4,500 meteres. It had lived and died on a distant seafloor that no longer exists. The shell in my palm was more than a fossil; it was evidence that the entire ocean can disappear and mountain ranges can rise where the ocean once stood. Experiences like this have shaped the way I think about geology. 

Listen to Jaishri Sanwal Bhatt explain about how she got enchanted by geology and time as a young child in the Indian Himalaya, and how she overcame obstacles and prejudices to begin a fruitful career as a field researcher in geology and paleoclimatology.

Explore the full InterDialogue with Sanwal Bhatt.

Imagine condensing the entire history of Earth into a single sentence. The opening words would describe a molten young planet forming from cosmic debris about 4.54 billion years ago. A few words later, the first oceans would appear. Life would emerge, transform the atmosphere with oxygen, survive episodes of near-global glaciation, and evolve from microscopic organisms into forests, dinosaurs, mammals, and eventually humans. Entire oceans would open and close. Continents would assemble into supercontinents and break apart again. Mountain ranges would rise and erode away. Five great mass extinctions would repeatedly reshape life’s trajectory. 

The fossil ammonite from Zanskar occupies only a tiny fragment of that sentence. Human civilization  occupies an even smaller one. Yet the rock beneath our feet preserves the whole story. 

The science of geology emerged from the recognition that Earth has a history¹ far older than any written record. Today we know that this history spans approximately 4.54 billion years, a time almost impossible to comprehend. If the entire history of our planet were compressed into a single calendar year, anatomically modern humans, who first appear in the fossil record roughly 300,000 years ago, would emerge only in the final half hour of December 31, at 11:25 p.m., while all recorded history would occupy the last few seconds before midnight. 

The earliest chapter of Earth’s history, the Hadean Eon (4.54 to 4.0 billion years ago), was a world of a molten surface, intense volcanism, and relentless asteroid bombardment beneath an atmosphere devoid of free oxygen. Yet even this seemingly hostile Earth registered significant clues. Zircon crystals from the Jack Hills of Western Australia, dated to ~4.4 billion years ago, contain geochemical signatures² indicating that liquid water already existed on Earth’s surface, suggesting that habitable conditions emerged far earlier than once believed. The principle is not unlike that of the isotopic studies I conducted on Himalayan paleolake sediments and speleothems: minerals retain the chemical fingerprints of the environments in which they formed. 

Figure 2. Working among the Proterozoic rocks of the Cuddapah Basin: (A) Panoramic view of the Proterozoic succession of the Cuddapah Basin. (B), Examining the ancient sedimentary rocks during fieldwork; (B). These outcrops preserve evidence of microbial ecosystems that flourished nearly 1.8 billion years ago and provide some of the geological clues used to reconstruct the chemistry of Earth’’s early oceans. Photographs: Author’’s field survey.

Although simple life had probably emerged earlier, the Archean witnessed its widespread diversification, fundamentally reshaping the chemistry of Earth’s surface environments. The succeeding Proterozoic Eon (2.5 billion to 540 million years ago) occupied more than 40% of Earth’s history and recorded some of the most profound transformations the planet has ever experienced. During geological investigations in the ancient rocks of the Cuddapah Basin in south India (Figure 2), the same broad geological province that includes the Gandikota gorge, I often found remarkable that these quiet landscapes capture the evidence of a world inhabited only by microscopic life. Banded iron formations and stromatolitic limestones from these successions record an Earth whose ocean, atmosphere, and biosphere differed fundamentally from those of today. Among the many revolutions recorded within Proterozoic rocks, none was more consequential than the gradual oxygenation of the atmosphere—a transformation that altered the chemistry of the planet and changed the course of biological evolution forever. 

The Great Oxidation Event: When Life Poisoned and Saved the World

If you could walk on the shore of the early Proterozoic Earth, you would not recognize the sky. There was no breathable oxygen, and the oceans were rich in dissolved iron, staining the waters the colour of rust. Yet in those ancient seas, a quiet revolution was already underway—not of armies or ideas, but of photosynthesis. 

Working in the Proterozoic outcrops of the Cuddapah Basin (Figure. 2 B), I have encountered rocks that bear witness to a vanished world, when only microbial life inhabited shallow seas and slowly transformed the chemistry of the Earth’s atmosphere and oceans. Among the specimens I collected during fieldwork are banded iron formations and stromatolites from the Vempalle Formation (Figure 3), gathered as part of a multidisciplinary study of natural hydroxyapatites with carbonate and actinide substitutions. The Cuddapah Basin hosts one of the world’s most unusual uranium provinces, where mineralization is strongly associated with the organic-rich laminae of stromatolites formed by cyanobacterial communities nearly 1.8 billion years ago. 

The uranium-bearing dolomites of the Vempalle Formation provide a significant record of how dissolved uranium was naturally trapped and immobilized within microbial mats during sedimentation. These stromatolites are important as archives of Earth’s early biosphere and as natural analogues for understanding the long-term behaviour of radionuclides in geological systems.

In one of our subsequent studies, conducted by an intern student, Mr. Jyotishko Ghosh from IISER, Thiruvananthapuram, India, under my supervision, a detailed morphological and geochemical investigation of the ~1.752-billion-year-old stromatolites revealed that subtle variations in magnesium concentrations and mineral composition retain the chemical signature of ancient seawater chemistry, allowing us to reconstruct changes in microbial growth and environmental conditions nearly two billion years ago. What fascinated me most was discovering that the same rocks preserving evidence of some of Earth’s earliest microbial ecosystems could also help answer a distinctly modern scientific question: how radionuclides become naturally immobilized within carbonate minerals over geological timescales. That connection gradually led to our research³ into the behavior of radionuclides⁴ in natural carbonates like cave speleothems⁵, demonstrating that geological archives formed billions of years ago can also help address contemporary challenges in environmental geochemistry and nuclear waste management.

Approximately 2.4 billion years ago, during the Siderian Period, microscopic cyanobacteria began transforming Earth’s chemistry forever. For hundreds of millions of years, they had released oxygen as a metabolic waste product, yet almost none reached the atmosphere; it was rapidly consumed by dissolved iron and other chemically reduced compounds abundant across the young planet. The evidence survives today in banded iron formations: spectacular alterations of iron-rich and silica-rich layers preserved on every continent, recording the gradual oxygenation of the oceans⁶ and atmosphere. The decline in widespread banded iron formation deposition after ~1.8 billion years ago marks a profound chemical transition—much of the dissolved iron had been removed from the ocean, allowing oxygen to accumulate in the atmosphere for the first sustained interval in Earth’s history.  

The rocks of Gandikota sit within this same Proterozoic interval. When I walked those quartzite ridges above the Pennar River gorge, I was standing on sediments deposited in a world already transformed by the Great Oxidation Event, a world in which the atmosphere’s chemistry had crossed a threshold from which there was no return. The rocks themselves carry no dramatic marker of that revolution. But knowing what they predate and postdate is part of what gives field geology its vertiginous quality: the sense that time is not linear but layered, and that you are always standing inside several geological chapters at once. 

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For the anaerobic organisms that had dominated Earth for nearly two billion years, the rise of oxygen was catastrophic. Oxygen is a highly reactive molecule, toxic to life evolved in its absence. The Great Oxidation Event likely triggered one of the deepest ecological crises⁷ the Earth has ever experienced, forcing anaerobic life into isolated refuges, where their descendants persist even today. The climate consequences were equally significant. Methane was then the atmosphere’s dominant greenhouse gas, compensating for a Sun that was 20–25% dimmer than today. Rising oxygen oxidized much of this methane into carbon dioxide and water. Because methane is a far more potent greenhouse gas than carbon dioxide, this weakened the greenhouse effect, contributing to global cooling and culminating in the Huronian glaciations. The stromatolites of the Vempalle Formation bear witness to the organism that produced the oxygen; the banded iron formation (Figure 3) records the chemical reactions that consumed it. Together, they are among the most consequential rocks on Earth.  

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Figure 3. Geological evidence of Earth’s early oxygenation from the Cuddapah Basin: (A) Banded iron formation, produced as dissolved iron in Precambrian oceans precipitated following the release of oxygen by photosynthetic cyanobacteria; (B) stromatolite from the Vempalle Formation, formed by layered microbial mats approximately 1.8 billion years ago. Together these rocks preserve complementary records of the biological and geochemical processes that transformed Earth’’s atmosphere and oceans. Photographs: Author’s field survey.

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It remains one of the great paradoxes of planetary evolution: life nearly destroyed the world it had inherited, only to create the conditions for a more complex one to emerge. Every breath we take today is a consequence of that ancient microbial revolution, still recorded in the rocks.  

Five Times the World Ended and Began Again

During my postdoctoral fieldwork in the Himalaya, while examining exposed rock horizons within the Palaeozoic strata of the Spiti Valley, I came across a trilobite fossil (Figure 4) embedded in a weathered limestone outcrop. Trilobites, a group of marine arthropods, thrived for nearly 270 million years and survived several major extinction events before ultimately disappearing during the end-Permian mass extinction, the greatest biological catastrophe in Earth’s history. Standing beside that outcrop, I was reminded that these mountains record far more than the record of continental collision; they also archive the extensive history of life’s evolution, resilience, and vulnerability.

The end of the world rarely announces itself. In the rocks, disaster often leaves behind only silence: a vanished reef, an empty fossil horizon, a sudden change in the chemistry where life once thrived. To a geologist, these thin boundaries mark moments when Earth reset itself, forcing evolution to begin again. The history of complex life has been punctuated by five great mass extinction events⁸—episodes during which more than 75% of species disappeared within geologically brief intervals. Each left an unmistakable signature in the stratigraphic record, driven by geological and geophysical forces operating at a planetary scale. Some of these boundaries I have encountered directly in the field. At Kashmir’s Guryul Ravine, the Permian–Triassic transition is preserved within a few meters of rock. In central India, the volcanic landscapes of the Deccan Traps record a different crisis: the eruption that coincided with the end-Cretaceous extinction is written into hundreds of meters of flood basalt. Other boundaries I have only studied through the work of geologists who have spent lifetimes piecing together the fossil record. Collectively, they form a planetary archive of catastrophe. 

The Ordovician extinction, ~443 million years ago, eliminated nearly 85% of marine species as rapid glaciation and falling sea levels occurred when Gondwana—the vast southern supercontinent that once united present-day South America, Africa, Antarctica, Australia, and the Indian subcontinent, drifted over the South Pole, followed by widespread oceanic anoxia, a severe depletion of oxygen in the oceans, as the climate abruptly shifted.

The Late Devonian extinction, ~375 million years ago, unfolded through multiple pulses⁹ linked to marine oxygen depletion and climatic instability as the expansion of land plants fundamentally altered the global carbon cycle. The Triassic extinction, ~201 million years ago, coincided with the eruption of the Central Atlantic Magmatic Province, whose enormous volcanic emissions triggered rapid warming, ocean acidification, and ecological collapse, ultimately clearing evolutionary space for the rise of dinosaurs. 

The most catastrophic of all was the Permian–Triassic extinction, often called the Great Dying, ~252 million years ago. Triggered largely by the prolonged eruption of the Siberian Traps, it eliminated approximately 90% of marine species and 70% of terrestrial vertebrates through extreme global warming, ocean acidification, widespread ocean anoxia, and declining atmospheric oxygen. During a recent field expedition to Guryul Ravine in the Kashmir Himalaya, accompanied by colleagues and students from the region, I spent a few days collecting fossils from one of the world’s most renowned sections preserving this very boundary (Figure 5). Standing beneath these towering rock cliffs, what struck me first was not dramatic scenery but a sense of understatement. The transition from the Late Permian Zewan Formation to the Early Triassic Khunamuh Formation, the boundary between the richest marine ecosystems of the Palaeozoic and the nearly barren oceans of the earliest Triassic, is preserved within only a few meters of laminated rock. There is no visible scar, rupture, or monument to catastrophe. 

The ecosystems that had flourished for millions of years simply vanish from the record, and new, sparse communities gradually take their place. It is precisely this restraint that makes the boundary so unsettling to witness, and a reminder that even the greatest biological crisis in Earth’s history survives today as little more than a subtle change in sediment layers and fossil assemblages. The geological record preserves destruction with extraordinary restraint.

The youngest of the five major extinction events occurred at the end of the Cretaceous period, approximately 66 million years ago. This event is most widely recognized for the Chicxulub asteroid impact which caused rapid and widespread ecological devastation. However, the stratigraphic record reveals a more nuanced narrative. At roughly the same time, the Deccan Traps of India, one of the largest volcanic features on Earth, were erupting at extraordinary rates, covering more than 500,000 square kilometers of the west-central Indian subcontinent in successive layers of flood basalt up to 2,000 meters thick in places. These eruptions released¹⁰ enormous volumes of volcanic gases into the atmosphere over hundreds of thousands of years and contributed prolonged environmental stress alongside the impact. Today, these basalt flows have weathered over millions of years to produce the fertile black cotton soils that sustain agriculture across Maharashtra and support millions of people. 

This transformation shows how landscapes shaped by catastrophe can become essential sources of life over geological timescales. I have explored these landscapes during fieldwork in the Deccan volcanic province and the dinosaur-bearing successions of central India. In my laboratory at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), I maintain a teaching collection of Deccan Trap crystals and mineral specimens, assembled with Mr. M. F. Makki, a mineral collector from Maharashtra. This collection allows students and visitors to engage directly with volcanic history. Examining minerals formed during one of Earth’s largest volcanic events provides a tangible link to the event 66 million years ago that shaped life on our planet. This broader interest in Earth’s history has also guided my research toward the younger geological records. 

My research has taken me to the Siwalik Hills, an excellent fossil-bearing sequence spanning from the Middle Miocene to the Middle Pleistocene (~16.8 to 0.5 million years ago), as well as to Quaternary fossil localities in the Kashmir Himalaya. Together, these terrestrial deposits preserve an exceptional record of environmental change and the evolution of early primates, extinct elephants, hominoids, and a diverse assemblage of large mammals across the Indian subcontinent. 

Through palaeontological investigations in the Kashmir Valley (Figure 6), including the description of Soriculus kashmiriensis—the first fossil Soriculus¹¹ recorded from the Indian subcontinent, recovered from the Plio-Pleistocene Karewa deposits and dated to approximately 2.4 million years ago—we have shown that fossil communities preserve detailed records of environmental and faunal change across a wide range of timescales. Although these Quaternary faunas became extinct under circumstances distinct from those of the major Palaeozoic and Mesozoic extinctions, they illustrate the same geological reality: extinction is a recurring process recorded throughout Earth’s sedimentary archive, from the greatest crises of deep time to the climatic transitions of the recent past.

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The five extinctions share a common lesson. Earth’s biosphere is remarkably resilient over geological timescales. The fossil record shows that even after the most severe crises, recovery took millions of years, with the Permian–Triassic extinction¹² alone requiring nearly 10 million years before ecosystems approached their former diversity. 

Yet that same biosphere is remarkably vulnerable¹³ on the timescales of human civilization. 

Following each of the five great mass extinctions, ecosystems typically require about five to ten million years to recover¹⁴ and regain their diversity. Today, biodiversity loss is estimated to be 100 to 1,000 times above the natural background levels, placing us, by the measure of the geological record, in the early stages of a sixth mass extinction¹⁵.

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Figure 6. From field to fossil: (A) Investigating the Plio–Pleistocene Karewa deposits of the Kashmir Himalaya, which preserve an exceptional archive of Quaternary environmental and faunal change; (B) Fossil specimens recovered from the Karewa deposits, including material used in the description of Soriculus kashmiriensis, the first fossil record of the genus from the Indian subcontinent (after Kotlia & Sanwal, 2005). Photograph from Author’s field survey.

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Snowball Earth: Total Glaciation and the Limits of Survival

Few ideas in geology are as unsettling as this: there was a time, perhaps more than once, when the Earth may have frozen almost entirely. Oceans lay sealed beneath thick ice extending to near the equator, glaciers covered much of the continents, and volcanoes continued releasing carbon dioxide into a silent, frozen atmosphere. At the equator, there may have been no open water, no forests, no familiar blue horizon—only ice stretching to the edge of sight beneath a pale and distant Sun. The planet had become its own mirror, reflecting sunlight back into space and deepening the freeze. And yet, life survived. 

That survival remains one of the most extraordinary facts in the geological record. Working among Himalayan glacial landscapes, I realized that ice has repeatedly reshaped our planet on scales that dwarf anything in the instrumental record. The Snowball Earth episodes represent the most extreme expression of ice as a geological force capable of transforming an entire planet. 

Between ~720 and 635 million years ago, during the Cryogenian Period, Earth experienced glaciations of astonishing severity. The Snowball Earth hypothesis, first proposed¹⁶ in modern form by Joseph Kirschvink in 1992 and supported by geological evidence¹⁷ from multiple continents, suggests that glaciers extended to near-equatorial latitudes. Among the strongest evidence are diamictites, unsorted glacial deposits containing boulders embedded within a fine-grained matrix, preserved in Cryogenian successions across Namibia, Australia, China, Scandinavia, and India. Their occurrence at ancient low paleolatitudes suggests that glaciation extended far beyond the polar regions. 

Yet recent research suggests that even during extreme glaciation, the climate system remained active. A 2026 study by Chloe Griffin and colleagues¹⁸ analyzed well-preserved varved from the Garvellach Islands off Scotland’s west coast, finding that during the Sturtian glaciation (the most intense Snowball Earth episode) climate patterns continued to operate on annual, decadal, and centennial timescales, with patterns resembling modern seasonal cycle and El Niño-like oscillations. These findings support the idea that Snowball Earth may have been punctuated by intervals of partial thaw, allowing limited atmosphere-ocean interaction to persist even under near-global ice cover.

The planet’s ultimate escape from this frozen state reveals the power of long-term geological feedback. Even beneath global glaciation, volcanic outgassing continued to release CO₂ into the atmosphere. With silicate weathering largely suppressed, atmospheric CO₂ accumulated over millions of years to concentrations far exceeding modern levels, eventually generating an intense greenhouse effect that drove rapid deglaciation¹⁹, possibly within only centuries to millennia. The transition from a frozen Earth to a greenhouse world may have been among the most dramatic climatic shifts in planetary history.

Life survived and may even have been transformed by the ordeal. Following the Marinoan deglaciation ~635 million years ago, the geological record reveals the first extensive diversification of large multicellular organisms—the Ediacaran biota. I first saw these fossils during my early scientific training, as a master’s student preparing thin sections and examining outcrops in the Nainital region of the Kumaun Himalaya. Observing ancient impressions of soft-bodied organisms preserved in Precambrian rocks, among the earliest complex life forms ever to exist, gave the abstract concept of post-glacial biological recovery an immediate and tangible reality. The environmental pressures imposed by Snowball Earth helped set the stage for the evolutionary developments²⁰ that culminated in the Cambrian Explosion. 

Snowball Earth offers an important lesson: geological upheaval, though often catastrophic, has never succeeded in terminating life. Instead, it sometimes redirects that history completely, creating evolutionary possibilities that could not have existed before. Ice is not only a force of destruction. Across Earth’s history, it has been one of the most powerful drivers of biological and environmental transformation.  

This is, in fact, the same lesson written across every chapter of Earth’s deep history. The Great Oxidation Event nearly eradicated the anaerobic organisms that had dominated the Earth’s biosphere for nearly two billion years, yet it produced an oxygen-rich atmosphere that enabled the evolution of complex life. Each of the five major mass extinctions eliminated a substantial proportion of existing species, yet created ecological conditions for new life to emerge, such as the rise of mammals following the extinction of the dinosaurs and the recovery of reef ecosystems after the Permian Great Dying, or new marine communities after the Ordovician glaciation. Even Snowball Earth, the most severe climatic episode in Earth’s history, gave way to the emergence of the Ediacaran biota and, ultimately, the Cambrian Explosion, which marked the rapid diversification of complex animal life as we know it. 

Listen to Jaishri Sanwal Bhatt track Earth’s “big history” through geological deep time. From origins to mass extinctions, from catastrophic events to explosions of life.

Explore the full InterDialogue with Sanwal Bhatt.

Viewed across geological time, these three episodes describe a planet that survived catastrophe and is repeatedly transformed by it. Life retreats, adapts, and re-emerges in forms made possible by the very crises that threaten its existence. 

Geology records every one of these transformations, patiently and precisely, in the chemistry of rocks, the succession of fossil assemblages, and the boundaries between geological formations. I have encountered these records directly, in the ancient rocks of Gandikota, in the Proterozoic stromatolites of the Cuddapah Basin, in the trilobite-bearing limestones of Spiti, and in the Ediacaran outcrops of the Kumaun Himalaya, where I first confronted the earliest complex life as a student. Each site added a sentence to a story the Earth has been composing for 4.54 billion years. 

The Story is Still Being Written…

That story does not end in deep time. It continues to be recorded in landscapes that are still being shaped by glaciers, monsoons, rivers, and active tectonics. Across these dynamic environments, geological proxies—including lake sediments, cave formations, fault scarps, river terraces, and coastal marshes where the ocean has left its mark—each preserve a different fragment of Earth’s recent past. 

Learning to read these natural archives has shaped much of my own scientific journey, revealing how the climate has shifted, mountains have risen and fractured, and oceans waves have repeatedly crossed the land. These are the newest chapters of Earth’s history, still being written, and waiting to be read. That journey continues in the next part of Earth’s memory.   

Banner image: Picture of Gandikota Gorge, Andhra Pradesh, India. A geologist pauses with compass in hand above the Pennar River, where nearly 300 meters of exposed Mesoproterozoic sedimentary sequences offer a rare window into Earth’s history nearly two billion years deep. Each horizontal band cut into these ancient quartzite and sandstone cliffs preserves a chapter written long before complex life emerged—a record of vanished seas, lost landscapes, and deep time inscribed in rock. Photograph: Author’s field survey, 2022.

Explore more images from the Author’s field survey.

Editor’s note: This original InterArticle is Part One of Jaishri Sanwal Bhatt’s “Earth’s Memory” series for The InterPlex.

1. Grotzinger, J. P., & Jordan, T. H. (2014). Understanding Earth (7th ed.). W. H. Freeman and Company.
   ↩︎
2. Wilde, S. A., Valley, J. W., Peck, W. H., & Graham, C. M. (2001). Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature, 409(6817), 175–178.
   ↩︎
3. Sanwal J., Dudwadkar, N.L., Thirumurugan, A., Tripathi, S.C., Gandhi, P.M. Satyam, P. V. and Sengupta, P. (2016). Adsorption of Ru, Ce and Eu radionuclides within naturally precipitated polycrystalline calcium carbonate under an acidic environment. Journal of Radioanalytical and Nuclear Chemistry, 309, 751–760.
   ↩︎
4. Sengupta, P., Sanwal J., Tripathi, S.C., Dudwadkar, N.L., and Gandhi, P.M. (2016). Adsorption of actinides within speleothem. Mineral Magazine, 80(5), 765–780. ↩︎
5. Sengupta, P., Sanwal J., Mathi, P. Mondal, J.A., Mahadik, P., Dudwadkar, N. and Gandhi, P. M. (2017). Sorption of Cs and Sr radionuclides within natural carbonates. Journal of Radioanalytical and Nuclear Chemistry, 312, 19–28. ↩︎
6. Holland, H. D. (2006). The oxygenation of the atmosphere and oceans. Philosophical Transactions of the Royal Society B: Biological Sciences, 361(1470), 903–915. ↩︎
7. Lyons, T. W., Reinhard, C. T., & Planavsky, N. J. (2014). The rise of oxygen in Earth’s early ocean and atmosphere. Nature, 506(7488), 307–315. ↩︎
8. Raup, D. M., & Sepkoski, J. J. (1982). Mass extinctions in the marine fossil record. Science, 215(4539), 1501–1503. ↩︎
9. Algeo, T. J., & Scheckler, S. E. (1998). Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 353(1365), 113–130. ↩︎
10. Schoene, B., Eddy, M. P., Samperton, K. M., Keller, C. B., Keller, G., Adatte, T., & Khadri, S. F. R. (2019). U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction. Science, 363(6429), 862–866. ↩︎
11. Kotlia, B. S., & Sanwal, J. (2005). The first fossil Soriculus (Tribe Soriculini) in the Indian subcontinent from the Karewas of Kashmir, India. Journal of the Geological Society of India, 65, 43–53. ↩︎
12. Erwin, D. H. (1994). The Permo–Triassic extinction. Nature, 367(6460), 231–236. ↩︎
13. Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O. U., Swartz, B., Quental, T. B., Marshall, C., McGuire, J. L., Lindsey, E. L., Maguire, K. C., Mersey, B., & Ferrer, E. A. (2011). Has the Earth’s sixth mass extinction already arrived? Nature, 471(7336), 51–57. ↩︎
14. Pimm, S. L., Jenkins, C. N., Abell, R., Brooks, T. M., Gittleman, J. L., Joppa, L. N., Raven, P. H., Roberts, C. M., & Sexton, J. O. (2014). The biodiversity of species and their rates of extinction, distribution, and protection. Science, 344(6187), 1246752. ↩︎
15. Ceballos, G., Ehrlich, P. R., & Dirzo, R. (2017). Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. Proceedings of the National Academy of Sciences, 114(30), E6089–E6096. ↩︎
16. Kirschvink, J. L. (1992). Late Proterozoic low-latitude global glaciation: The snowball Earth. In J. W. Schopf & C. Klein (Eds.), The Proterozoic biosphere: A multidisciplinary study (pp. 51–52). Cambridge University Press. ↩︎
17. Hoffman, P. F., Kaufman, A. J., Halverson, G. P., & Schrag, D. P. (1998). A Neoproterozoic snowball Earth. Science, 281(5381), 1342–1346. ↩︎
18. Griffin, C., Rugen, E., Gernon, T. M., Spencer, A. M., & Hincks, T. K. (2026). Interannual to multidecadal climate oscillations occurred during Cryogenian glaciation. Earth and Planetary Science Letters, 679, 119891. ↩︎
19. Pierrehumbert, R. T., Abbot, D. S., Voigt, A., & Koll, D. (2011). Climate of the Neoproterozoic. Annual Review of Earth and Planetary Sciences, 39, 417–460. ↩︎
20. Knoll, A. H. (2003). Life on a young planet: The first three billion years of evolution on Earth. Princeton University Press. ↩︎