Overview

Where the 2.4 Myr and 405 kyr eccentricity cycles are grounded in exact celestial mechanics, the 26–27 Myr cycle sits at the opposite end of the evidentiary spectrum: a periodicity detected purely statistically, in the timing of mass extinctions and other major geological events, whose cause remains genuinely unresolved after more than four decades of research. It is also one of the best-tested — repeatedly re-run against revised geological timescales, richer datasets, and independent event categories, and it keeps surviving.

The original discovery

The signal was first identified by David Raup and John Sepkoski in 1984. Analyzing the extinction intensity of marine animal families over the preceding 250 million years, they found 12 extinction events showing statistically significant periodicity (P < 0.01), with a mean interval of 26 million years between them — a finding immediately controversial because two of the events lined up with the terminal-Cretaceous and Late Eocene extinctions already tied to meteorite impacts. This raised the "Nemesis" hypothesis: that the Sun might have an undetected companion star in a wide, eccentric orbit, periodically disturbing the Oort Cloud and showering the inner solar system with comets.

The finding was attacked on statistical grounds almost immediately. Stigler and Wagner argued that the coarse resolution of the 1980s geological timescale — with stage boundaries themselves spaced fairly regularly — could manufacture an apparent periodicity out of essentially random extinction timing. Raup and Sepkoski countered with genus-level data (finer-resolution than families) and continued to find the same 26 Myr signal, though they acknowledged the debate needed more data to settle.

Re-confirmation with better data: 26 → 27 Myr

That better data arrived in two major waves.

Melott & Bambach (2010) reanalyzed both the Sepkoski genus compendium and the newer Paleobiology Database, using the revised 2004 geological timescale, and extended the record back to 500 million years — twice as far as the original study. They found a periodicity of 27 million years, confirmed at 99% confidence, with the shift from 26 to 27 Myr essentially just a bookkeeping consequence of the geological timescale itself having grown about 3% longer since 1984. Notably, they used the increased regularity of the signal to argue against the Nemesis hypothesis: a real companion star's orbit would have been perturbed by the many stellar encounters the Sun has had over 500 million years, which should smear the periodicity out — yet the interval stayed metronomically regular, which better fits a mechanism more stable than a distant, gravitationally jostled star.

Melott & Bambach (2013), following the 2012 revision of the international geological timescale, repeated the analysis again with even finer taxonomic resolution (genera rather than families). The 27 Myr periodicity not only survived but came through with improved statistical significance, and the excess of extinction events lining up with the periodicity's predicted maxima was confirmed at the p ≈ 0.01–0.02 level across the full Phanerozoic.

Beyond extinctions: a broader geological pulse

Independently, Michael Rampino and collaborators have spent over three decades documenting a closely related periodicity — usually reported as 26–30 Myr — not just in extinctions but across a much wider range of geological phenomena: continental flood-basalt eruptions, major plate-tectonic reorganizations, ocean-anoxic events, sea-level fluctuations, intraplate magmatism, and marine strontium-isotope excursions. A 2026 synthesis by Rampino compiling 89 major geological events over the last 260 million years found them clustering into 10 peaks spaced roughly 26 million years apart — extinctions, flood basalts, and anoxic events tending to co-occur within the same peaks rather than scattering independently, which is itself a striking result: it suggests a single underlying pacer rather than several coincidentally similar but separate cycles. The most recent estimate from this broader dataset, released in 2026, puts the period at 27.5 million years, with a much weaker secondary signal near 8.9 Myr.

The unresolved question: what causes it?

Unlike the 2.4 Myr and 405 kyr cycles, no candidate mechanism for the 26–27 Myr cycle has anything like a settled physical derivation. Three broad classes of explanation remain in competition:

1. Internal Earth processes. Deep-mantle plume cycles or convective overturns could plausibly drive periodic flood-basalt volcanism and associated extinctions on multi-million-year timescales, without needing any astronomical trigger at all.

2. Galactic-plane crossings. As the solar system orbits the galactic center, it periodically passes through the crowded mid-plane of the Milky Way's disc, which could gravitationally perturb the Oort Cloud and increase cometary bombardment — a revival, in modified form, of the old Nemesis idea, but driven by galactic structure (including, in some versions, a hypothesized thin disc of dark matter) rather than a companion star. Rampino and others have shown correlations between impact-crater ages, extinction pulses, flood basalts, and estimated galactic-plane-crossing times, with roughly 6 of 13 proposed impact pulses over 260 Myr lining up with plane crossings in one widely used model (Randall & Reece 2014).

3. Very long-period orbital/climatic forcing on the crust. A more speculative proposal is that long-term redistribution of water, ice, and sediment via slow orbital or climatic cycles subtly alters crustal and mantle stresses, encouraging episodic tectonic and volcanic activity — an indirect, climate-mediated route rather than a direct astronomical trigger.

None of these has been confirmed, and Rampino's own recent framing treats the question as explicitly open, with the resolution likely to depend on tightening the radiometric dates of the largest flood basalts and impact craters — some of which already carry uncertainties at or below a million years, small enough that a few more precise dates could start to discriminate between the competing mechanisms.

Cross-check against your own analysis

This is one of the few long cycles where independent, modern statistical methods keep landing on essentially the same number from essentially the same class of data: Raup & Sepkoski's original 26 Myr, Melott & Bambach's 27 Myr (2010, reconfirmed 2013), and Rampino's 26–27.5 Myr figure from a much broader, non-extinction-only event set. Your own CATS run on the Puetz marine-genera dataset returned 27.15 Myr, and an independent Lomb-Scargle periodogram on the same raw data reproduced it almost exactly (27.15 Myr) — sitting right in the middle of this now four-decade-long, repeatedly-revised literature consensus.

Key sources

• Raup, D.M. & Sepkoski, J.J. (1984). Periodicity of extinctions in the geologic past. PNAS 81, 801–805.

• Melott, A.L. & Bambach, R.K. (2010). Nemesis Reconsidered. MNRAS Letters 407, L99–L102.

• Melott, A.L. & Bambach, R.K. (2013). Do periodicities in extinction — with possible astronomical connections — survive a revision of the geological timescale? ApJ 773, 6.

• Rampino, M.R. & Caldeira, K.; Rampino, M.R. et al. (2019, 2021a, 2021b) — series of papers on ~26–30 Myr periodicity across flood basalts, anoxic events, sea-level change, and intraplate magmatism.

• Rampino, M.R. (2015). Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events. MNRAS 448, 1816.

• Randall, L. & Reece, M. (2014). Galactic-plane-crossing model referenced in Rampino's impact/extinction correlation work.

• Rampino, M.R. (2026). The temporal characteristics of the geologic record: Global correlations and similar multi-million-year cycles of major geologic events, with potential internal-Earth versus astronomical causes — 89-event, 260 Myr synthesis giving 27.5 Myr with a secondary 8.9 Myr signal.

The following Biography of S L Afanasiev was provided to me by his daughter M.S. Afanaseva who is the joint author of it. I am selecting only the parts that are most relevant to his geology studies in particular resulting in his book on the Nanocycles Method. His parents lived through the Russian revolution and had horrific experiences and I have omitted these details. These experiences surely played some part in S L Afanasiev choosing his own given name at the age of 5.
SERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"M.S. Afanaseva and L.V. KonstantinovskayaOUTSTANDING GEOLOGIST, CHAIRMAN OF THE SECTION OF THE MOSCOW SOCIETY OF NATURALISTSSpartak Leonidovich Afanasiev-Yakobson(1923-2014)"The descendant of our vigils will not forget. Now the path to knowledge is open to him: let the cyclite built in battle be our common monument."S.L. AfanasievSpartak Leonidovich was born on December 11, 1923 in Moscow to Leonid Georgievich Afanasyev and Natalia Georgievna Yakobson (née Belokonskaya).
Spartak Leonidovich spent his childhood in Moscow on Sadovo-Karetnaya Street. At the age of five, his grandmother, Lyubov Matveyevna, told her grandson Yurochka about the slave revolt in ancient Rome led by Spartacus. Yurochka decided he was Spartacus and announced it to everyone. When he started school, his parents were asked, "What's your son's name?" "Actually, we named him Yura, but he wants to be Spartacus. Call him Spartacus." The name Spartacus was first recorded on his Komsomol membership card.Spartak was fascinated by geology from childhood: he became acquainted with the spines of sea urchins, the segments of sea lilies, and irregular shells whose plane of symmetry is located not along the shell, but across it, called brachiopods. And in the geography club at the Moscow City House of Pioneers and Octobrists on Stopani Lane (now Ogorodnaya Sloboda), he first learned the meaning of geological terms, the meaning of the indices Q, N, Pg, Cr, J, T, P, C, and D, and the colors used in geological maps.In 1939, the Moscow House of Pioneers organized a two-week excursion to the Otuz Valley in Crimea. Spartak and his comrades were captivated by Kara-Dag, the sea, and the air of freedom. One day, standing before a banded stone, Spartak said, "They lie like the pages of a book," and he spent the rest of his life studying banded stones, or cyclites. He brought back 40 kg of stones to Moscow, along with a box of beautiful geological specimens: quartz druse, calcite, carnelian, agate, and jasper. In the summer of 1940, the Young Naturalists' Station organized a children's geological expedition to the Urals. The children crossed the border between Europe and Asia near Lake Turgoyak, and in the Ilmensky Mineralogical Reserve, they encountered crystals of topaz, beryl, amazonite, large crystals of biotite, and numerous rare minerals. School geological expeditions to the Crimea and the Urals finally determinedEgor Klimanov. Water transport https://fleetphoto.ru/vessel/1098/obrashcheniya: 15.08.2022). (Date
SERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"Spartak's calling was to become a geologist. Spartak graduated from School No. 368 in Sokolniki. As an excellent student, he was admitted to the Sergo Ordzhonikidze Moscow Geological Prospecting Institute (MGRI) on June 20, 1941, without taking exams.The Great Patriotic War. In the summer of 1941, Spartak took part in the construction of a bomb shelter near Sokolniki Park. Then he was sent by the Komsomol Central Committee to Derbent for agricultural work, harvesting grapes. But he was unable to return to Moscow and, with great difficulty, made his way along the Volga to Gorky.In Gorky, Spartak joined the Krasnoye Sormovo plant, which was then producing T-34 tanks. He worked first as a lathe operator's apprentice, then as a fourth-class lathe operator. Later, he worked primarily at seventh and sometimes at eighth class. He worked 12-hour shifts with an hour-long lunch break. True, food, like everywhere else, was scarce. At the plant, they served bran noodle soup, mashed potatoes for the second course, and unlimited hot salty water for the third. His constant thought was: where to eat? He lived almost entirely on 800 grams of bread a day. During their winter lunch breaks, the lathe operators would warm themselves near the pipes and dream: summer will soon be here, sorrel, stilt grass, and wild onions will be in season. tablespoonSpartak slept in the factory dormitory, where the large hall (formerly a movie theater) was stacked with two-story iron beds. In the summer of 1942, he slept on a felt mat in the workshop. He didn't have to walk the three kilometers to and from the dormitory during the summer, so he had more time to prepare for his first-year exams at the Moscow State Geological Survey.The plant had a technical school, but not a geological one. The geology department was at the Gorky Institute. But traveling to Gorky was difficult, mainly because of the time involved. On a friend's advice, Spartak enrolled in a technical school specializing in cold metalworking. The director of the technical school admitted him to the third year without any documents.Student years. In 1943, Spartak's mother transferred his application for admission to the Moscow State Geological Prospecting Institute (MGRI) to the Institute of Non-Ferrous Metals and Gold, since he had the right to be called to classes, while MGRI did not. Spartak was a student at the Institute of Non-Ferrous Metals and Gold for 25 days. At the same time, he took his first-year exams at MGRI. He received excellent and good grades, but struggled with mathematics and decided to enroll in his first year at MGRI, not his second.In 1945, Spartak, as an excellent student, was awarded a Stalin scholarship and elected to the Komsomol committee and the MGRI trade union. In May 1947, he married fellow student Masha Eremina, and they had a daughter, Marina.Student internships took place in 1946 and 1947 in the Carpathians, as part of the MGRI Carpathian Expedition. They often went on routes accompanied by border guards, since they repeatedlyTHE FATES OF THE CREATORS OF RUSSIAN SCIENCE AND CULTUREVOLUME 10But they met with Banderites. Alexey Alexeyevich Bogdanov instructed against any political discussions with local residents, and all documents were left in Lviv. Based on his work in the Carpathians, Spartak published his first scientific article: "Geology of Paleogene Deposits in the
Western Part of the Transcarpathian Region" (Afanasyev, 1949). In 1947, the Student Scientific Society was established at MGRI. Spartak was elected Chairman of the SSS Council, and Gleb Kaleda his deputy. A school sector was organized within the SSS, which later became the school faculty. Students began organizing geological clubs in Pioneer Houses and schools, formed friendships with the Leningrad SSS, visiting them, and hosting representatives of the Leningrad SSS.Two Moscow meetings were organized and held, based on the resultsin which student reports were published in 1949 and 1950.Beginning of his career. After graduating from MGRI, Spartak Leonidovich initially worked as a foreman for Nikolai Mikhailovich Strakhov at the Institute of Geological Sciences of the USSR Academy of Sciences (now the Geological Institute of the Russian Academy of Sciences).In 1950, he joined the Museum Expedition of the Moscow State University Geology Research Institute as a junior research fellow. In the summer of 1950, the expedition worked in the Tien Shan and Pamirs, collecting geological samples for the Moscow State University Museum of Geosciences. Along the Naryn River, Spartak Leonidovich described a section of Carboniferous carbonate layered deposits, and along the Isfayram River, near the mouth of the Tegermach, he compiled a 375-meter-thick carbonate section of the Upper Devonian–Lower Carboniferous layer by layer.On April 26, 1951, Spartak Leonidovich was arrested as the son of an enemy of the people and exiled to the Sukhobuzimsky District of Krasnoyarsk Krai for five years. In December 1951, Spartak Leonidovich, while in the village of Tatarskoye, began working as a senior worker in the survey party of the Krasnoyarsk Design Office of the Krai Agricultural Administration. In the spring of 1952, geologists arrived. They asked for a secondment. Spartak was chosen. The workers drilled shallow boreholes by hand, and the foreman described the core. Spartak Leonidovich suggested the Jurassic age of the core, which caused a sensation. Spartak was immediately promoted from senior worker to senior technician, equipped with a theodolite, and given the task. But the work of geologists in the Sukhobuzimsky district ended, and Spartak was relieved of his duties in the office due to the impossibility of using him for work in other districts of the Krasnoyarsk Territory. In the autumn of 1952, Spartak Leonidovich was transferred943 Afanasyev Spartak Leonidovich. // Repressed geologists. Biographical materials. 2nd ed. Moscow, St. Petersburg, 1995. - P. 14.944 Afanasiev-Yakobson Spartak Leonidovich. // Blokh Yu., Skoptsova V. Repressed MGRI geologists. Version 1.2 M., 2018. – P. 90.SERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"He was sent to the village of Shilinka in the Sukhobuzimsky District, where he found work as a draftsman at P.O. Box 126, Krasnoyarsk-2. He was assigned to draw the façade of the Beloyarsk Power Plant. The work was completed, and the Beloyarsk Power Plant still exists today. In March 1953, Spartak Leonidovich's wife, Maria Mikhailovna, and their young daughter, Marina, came to Shilinka. But in June, they all returned to Moscow after an amnesty was declared.After returning from exile in Krasnoyarsk, Spartak Leonidovich spent three years as a senior geologist with the Krasnodar Geological Exploration Expedition of the Mosgeolnerud Trust. He was one of the discoverers of the richest limestone deposits for the Novolipetsk Metallurgical Plant;
in the Tuapse region, he participated in the exploration of the Krivenkovskoye limestone deposit on the slopes of Mount Neveb.Lomonosov Moscow State University. After his rehabilitation on May 26, 1956, Spartak Leonidovich was given the opportunity to join the Moscow State University Caucasus Expedition as a geologist, and later as a team leader. The Moscow State University Caucasus Expedition was established in 1955 on the initiative of Professor A.A. Bogdanov, Head of the Department of Historical and Regional Geology. G.D. Azhgirey led the expedition, and V.E. Khain led the westernmost party from Adler to Anapa.Spartak Leonidovich led one of the teams in V.E. Khain's party 945, 946. He and his team mapped the area between Anapa, Novorossiysk, Gelendzhik, and Tuapse, surveyed flysch strata on the Black Sea coast with centimeter-level accuracy, and then continued the same line of work in the Carpathians. In the fall of 1960, on the recommendation of Nikolai Mikhailovich Strakhov, he became a graduate student under Viktor Efimovich in the Geology Department of Moscow State University.While working on the Caucasus Expedition, Spartak Leonidovich participated in assessing Novorossiysk's "gray gold" reserves of marly limestone, a native raw material for the production of high-quality cement at the Novoroscement cement plants. Geologists noted gas shows in the Pshada-Shapsukho interfluve, and at their suggestion, the Doobskaya well was drilled. In 1963, a gas field was discovered in the Doobskaya area.The Caucasian expedition was replaced by the Carpathian one, organized and headed by V.I. Slavin. Spartak Leonidovich led one of the parties of the Carpathian expedition of Moscow State University in 1961-1963. On January 18, 1963, in Leningrad at the Uche-945 Khain V.E. From the memoirs of a geologist. Moscow: GEOS, 1997. – 188 p.946 Khain V.E. Days of my life: (memories of a geologist). – M.: Scientific World, 2009. – 223 p.THE FATES OF THE CREATORS OF RUSSIAN SCIENCE AND CULTUREVOLUME 10The VNIGRI Scientific Council successfully defended Afanasyev's candidate dissertation, "Upper Cretaceous–Lower Paleocene Flysch Formation of the Northwest Caucasus." The doctoral dissertation took Afanasyev a long time to prepare; on December 29, 1989, it was successfully defended at the Academic Council of the Geological Faculty of Moscow State University.Scientific directions. Flysch formations are formed at the foot of materic slope. They are typical representatives and indicators of the perioceanic type of lithogenesis. Spartak Leonidovich dedicated his entire scientific life to studying the formation conditions and structural patterns of flysch formations.Beginning in 1946, Spartak Leonidovich processed and studied a vast amount of factual material collected during geological survey expeditions and through personal research in the Caucasus, Altai, the Siberian and Russian platforms, the Carpathians and Tien Shan, the Sayan Mountains, and Western Siberia. In the Greater Caucasus alone, he studied and layer-by-layer described over 300 Upper Cretaceous sediment sections, comprising approximately one million layers. Based on his study of this colossal body of factual material, he arrived at highly interesting and revolutionary
conclusions about the structure of Upper Cretaceous lithologies in the Greater Caucasus, the structural patterns and formation conditions of flysch formations, and the determination of geological age using nanocycles. His extensive scientific training, interest in science, and geological instinct helped him correctly evaluate the data obtained and, for the first time, develop a method for studying flysch formations, create a detailed stratigraphic scheme of the Greater Caucasus, and propose an innovative nanocyclite method for determining geological age.The problem of cycles and rhythms has been resolved. Cyclites are defined by their duration, measured in seconds. Rhythms are measured in hertz, or seconds to the power of minus one. Geological bodies at all levels of organization form cyclites, i.e., successive series of lithomes reflecting the spiral turns of geological development from pulsites and microlayers to the Earth's crust as a whole. For all categories of cyclites, the first elements are defined by an increased sedimentation rate, the second by a decreased sedimentation rate.Duration of lithome development: determined by the nanocyclite method based on fluctuations in the thickness of sandstone and siltstone layers in rocks with a horizontal microlayered texture. Using tables of nanocyclite spectra, the nanocyclite age in millions (thousands) of years is determined with high accuracy. Time estimates made it possible to identify 21 classes of cyclites and evaluate the reliability of interzonal correlation of sections. Mega-, macro-, meso-, micro-, nano-, and picocycles are distinguished. Based on the cyclesSERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"A Phanerozoic nanocyclite geochronological scale has been constructed and published. Thirty-three complexes of cycles and rhythms, ranging in duration from one tertium to 5 billion years, have been published.However, Spartak Leonidovich also encountered opposition to his ideas about the cyclical nature of flysch formations, which made him a consistent champion and advocate of this scientific approach. Afanasyev wrote: "The 'flysch formation hypothesis' must include and take into account completely different methods of formation of various layers of flysch assemblage. However, the bulk of the rocks in the axial parts of a flysch trough are nevertheless formed from material from turbidity currents. The development of a flysch formation over time is characterized by the replacement of relatively long, stable periods by comparatively short, unstable periods. During stable periods, slow, particle-by-particle sedimentation of predominantly biogenic deposits occurred over the course of several geological seconds." During unstable periods, when there was a relatively small drop in the level of the World Ocean, often accompanied by a sharp increase in seismicity, and sometimes volcanic activity of deep faults limiting the flysch trough, the balance was disturbed.Large collapses and landslides of marl-limestone and sand-silt-silt material led to the formation of underwater landslides, which developed into turbidity flows, which, sliding down the slope, transported debris to the axial part of the trough, where it was picked up by a constantly acting unidirectional median current and spread throughout the entire flysch trough.The alternation of seismic activity periods with stable periods was the primary cause of the formation of flysch cyclicity. Cyclites of class 21 are distinguished by their duration. In the flysch formation, cyclites of classes 6-13 are most clearly manifested, with an average duration of 14 million years to 220 years. 947
Teaching activities, students. Spartak Leonidovich was not only one of the most prominent geologists in Russia and carried out extensive scientific work, but was also a remarkable teacher. He participated in educational and upbringing work. For half a century, from October 1963, Spartak Leonidovich worked as an associate professor and professor in the Department of Geology and Hydrogeology at the All-Union Correspondence Polytechnic Institute (VZPI), on the basis of which the Moscow State Open University named after V.S. Chernomyrdin (MGOU) was created in 1992. In 1992, Spartak Leonidovich was awarded the academic title of professor of MGOU. Afanasyev S.L. was947 Afanasyev S.L. Geology of the Western Caucasus. Moscow: Voentekhizdat, 2004.THE FATES OF THE CREATORS OF RUSSIAN SCIENCE AND CULTUREVOLUME 10the academic supervisor of the candidate's dissertation of the Moscow State University postgraduate student Lyudmila Vasilievna Konstantinovskaya, who successfully defended her dissertation at the Academic Dissertation Council of the Geological Faculty of Moscow State University (1998), and subsequently became an associate professor of the Ecology Faculty of Peoples' Friendship University of Russia (RUDN).Scientific legacy. During his time at VZPI-MGOU, Spartak LeonidovichHe has published numerous scientific papers, geological excursion guides, and textbooks. He researched flysch formations and wrote his doctoral dissertation, "Flysch Formation: Patterns of Structure and Formation Conditions." The results of his research are used in his lectures and laboratory work with students. At VZPI, he taught original lecture courses: "Main Structural Elements of the Earth's Crust," "Structural Geology and Geological Mapping," and "General and Regional Geotectonics."Spartak Leonidovich left a vast scientific legacy in many fields: lithology, flysch formations, natural cycles, mathematical methods, stratigraphy, correlation, tectonics, and geochronology. He published 373 scientific papers, including:four monographs devoted to the deposits of the flysch formation of the Western Caucasus, the problems of studying geological time and the nanocyclite method of determining geological age;articles in publications: Geology of the USSR (volume IX, 1968), Stratigraphic Dictionary of the USSR (Triassic, Jurassic, Cretaceous, 1979; Paleogene, Neogene, Quaternary system, 1982) and Stratigraphy of the USSR (Cretaceous System, 1986);Geological map and map of mineral resources of the USSR (Caucasian series, 1971);- excursion guides for the IV and VI All-Union and X International School of Marine Geology (Moscow: Institute of Oceanology, 1980, 1984, 1992).Spartak Leonidovich's scientific legacy remains highly sought after by geological science and industry today. A new methodology for studying flysch formations has contributed to the increased efficiency of geological exploration in complex flysch formation development areas in the Caucasus, Carpathians, Central Asia, Siberia, the Sayan Mountains, and other regions. The nanocyclite method was used to determine the age of several units of Jurassic oil-bearing deposits
in Western Siberia, Quaternary formations along the Ob, Irtysh, and Yenisei rivers, Vendian oil-bearing rocks in the Eastern Sayan Mountains, and Sarmatian deposits in Taman. The paleotectonic scheme of the Greater Caucasus has improved the efficiency and quality of mineral deposit forecasting. The developed methodology for studying flysch formations and the detailed stratigraphic scheme of the Greater CaucasusSERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"The nanocyclite method for determining geological age is still successfully used without modification by researchers in Russia, Armenia, Georgia, and Azerbaijan. Today, geologists conducting research in the Tuapse region, near Novorossiysk and Anapa, rely on the work of this outstanding figure.The Moscow Society of Naturalists (MOIP) Intersectional Seminar (Commission) "Mathematics in Geology" was founded in 1964 by Professor Mark Vladimirovich Ratz, who served as its first chairman. In 1970, Spartak Leonidovich took over as the seminar's chair, and Lyudmila Vasilyevna Konstantinovskaya, PhD in Geology and Mineralogy and Associate Professor at Peoples' Friendship University of Russia (RUDN), became the permanent Academic Secretary. The Commission consisted of 50 full members (including six doctors of science and 18 candidates of science), representing 15 organizations.Seminars were held regularly, approximately once a month, at the Polytechnic Museum or the Moscow State University Zoological Museum. These seminars focused on two main topics: "Space and Cycles" and "Geological Cycles and Their Relationship to Space." More than 650 papers were presented. Every even year, beginning in 1982, international conferences under the general title "Mathematical Methods for Analyzing Cyclicity in Geology" were held at the Moscow State University of Geology. Scientists from Russia, Georgia, Zambia, Kazakhstan, Canada, and Ukraine presented at the conferences. Since 1984, 15 collections of scientific papers have been published based on the materials of these seminars and conferences, containing over 600 papers. The conference proceedings have been used in the educational process at Moscow State University of Geology, Peoples' Friendship University of Russia, and Moscow State University.The MOIP Intersectional Seminar (Commission) closely cooperates with many scientific organizations and associations: Lomonosov Moscow State University, Chernomyrdin Moscow State Open University, Vernadsky Geological Museum, Sternberg State Astronomical Institute, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences, Peoples' Friendship University of Russia, Academy of Forecasting (section "Security: Threat from Space"), "Forecasts and Cycles" Association, World Data Center for Solar-Terrestrial Physics, Polytechnic Museum, Russian Geographical Society, Stavropol Scientific Center "Cycles of Nature and Society", Helios Foundation for the Promotion of the Scientific Heritage of A.L. Chizhevsky, N.D. Kondratieva, the F.Yu. Zigelev Foundation. Together, they hold roundtables and conferences, and publish joint collections of scientific papers.THE FATES OF THE CREATORS OF RUSSIAN SCIENCE AND CULTUREVOLUME 10Awards and membership in academies in Russia and abroad. Spartak Leonidovich was awarded the medals "Forty Years of Victory in the Great Patriotic War 1941-1945", "For Valiant Labor in the Great Patriotic War 1941-1945", "50 Years of Victory in the Great Patriotic War 1941-1945"; medals in commemoration of the 800th and 850th anniversaries of Moscow; the Honorary Diploma
of the Moscow Society of Naturalists; the "Higher School", "For Excellent Achievement in Work" badges in the field of higher education, "Geological Service of Russia"; the N.D. Kondratyev medal.Afanasyev S.L. was a full member of the International Academy of Mineral Resources (IAMR, 1994), the International Academy of Informatization (MAI, 1994), and the Russian Academy of Natural Sciences (RANS, 1998). Spartak Leonidovich was a member of the Council of MOIP and its honorary member. For 30 years of educational work and leadership of the "Mathematics in Geology" section, he was awarded an honorary diploma of MOIP (2013). Spartak Leonidovich was a very sociable, energetic, and cheerful person. He sang well, with a strong and very pleasant voice. He wrote poetry and short stories about the lives of the inhabitants of Losinny Ostrov National Park, where he loved to walk. Despite all the trials and tribulations of life, he was an optimist. He always tried to help people in difficult situations. He was very attentive and kind to students, graduate students, and colleagues.Spartak Leonidovich passed away on May 5, 2014, and was buried in Moscow at the Novodevichy Cemetery.Selected Works of S. L. AfanasyevAfanasyev S.L. Geology of Paleogene deposits of the western part of the Transcarpathian region. // Scientific works of students of mining and metallurgical institutes of Moscow. M., 1949. - P. 45-69.Afanasyev S.L. Guide to the excursion of the IV All-Union School of Marine Geology. Upper Cretaceous flysch formation of the North-West Caucasus. Moscow: Institute of Oceanology, 1980. – 34 p.Afanasyev S. L. Upper Cretaceous flysch formation of the North-West Caucasus: Guidebook of the excursion of the VI All-Union School of Marine Geology, Gelendzhik, 1984. – M.: Institute of Oceanology, 1984. – 56 p.Afanasyev S.L. Geochronological scale of the Phanerozoic and the problem of geological time. Moscow: Nedra, 1987. – 143 p.Afanasyev S.L., Arkhipov A.A. Nanocyclite method for determining the geological age of Quaternary deposits. Novosibirsk: "Nauka", Siberian Branch, 1990. - 122 p.SERIES "MOSCOW UNIVERSITY: EPOCHS AND PEOPLE"Afanasyev S.L. Nanocyclite method for determining geological age by microlayers, varves, and salt layers. Moscow: VZPI Publishing House, Rosvuz-nauka JSC, 1991. – 216 p.Afanasyev S.L. Geology of the Western Caucasus. – M.: Voentekhizdat, 2004. 167 p.

First published: 2026

Brief summary

Review of multi-million-year cyclicity in major geologic events (extinctions, impacts, volcanism) comparing internal-Earth versus astronomical pacing mechanisms, with updated crater and extinction datasets.

Article

The Temporal Characteristics of the Geologic Record: Global Correlations of Multi-Million-Year Cycles is a peer-reviewed journal article published by Earth-Science Reviews (ScienceDirect) in 2026. It reviews multi-million-year cyclicity in major geologic events (extinctions, impacts, volcanism) comparing internal-Earth versus astronomical pacing mechanisms, with updated crater and extinction datasets.

The analysis focuses on ~26-30 My cycle in mass extinctions and impact craters. The study includes figure comparing crater-formation rate for 37 dated craters against 12 marine extinction times. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: An apparent cycle of 26-My to 30-My in the record of marine mass extinctions over geologic time was followed by the discovery of a similar cycle in coincident mass extinctions of vertebrates on land, and in the ages of dated impact craters. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together geologic cycles, mass extinctions, impact craters, volcanism. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a peer-reviewed journal article, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: Earth-Science Reviews (ScienceDirect)
• Source type: Peer-reviewed journal article
• URL type: WWW
• Credits: Earth-Science Reviews (ScienceDirect)
• URL: https://www.sciencedirect.com/science/article/pii/S2950117226000129

First published: 2025

Brief summary

Finds ~26-36 My cycles common to stratigraphic sequence boundaries, tectonism, sea-level, climate and biotic change, potentially linked to modulation of Earth's 2.4-My and 9-My orbital eccentricity cycles.

Article

Correlation and Cyclicity of Stratigraphic Sequence Boundaries and Chronostratigraphic Stage Boundaries of the Last 253 My is a peer-reviewed journal article published by Earth-Science Reviews (ScienceDirect) in 2025. It finds ~26-36 My cycles common to stratigraphic sequence boundaries, tectonism, sea-level, climate and biotic change, potentially linked to modulation of Earth's 2.4-My and 9-My orbital eccentricity cycles.

The analysis focuses on ~26-36 My. It also considers also references orbital eccentricity modulation cycles of 2.4 My and 9 My. The data source is global stratotype (GSSP) chronostratigraphic record spanning 253 My. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: Similar ~26 to 36 My cycles have been reported in various forms of tectonism, intra-plate volcanism, climatic change, ocean anoxia, biodiversity and mass-extinction events, implying causal linkages among these phenomena. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together stratigraphic cyclicity, sequence boundaries, 26–36-million-year cycles, orbital eccentricity. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a peer-reviewed journal article, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: Earth-Science Reviews (ScienceDirect)
• Source type: Peer-reviewed journal article
• URL type: WWW
• Credits: Earth-Science Reviews (ScienceDirect)
• URL: https://www.sciencedirect.com/science/article/abs/pii/S0012825225000613

First published: 2024

Brief summary

Accessible overview explaining that stratigraphic cycles occur at scales from millimetres to hundreds of metres thick, driven by sea-level, sediment supply, and tectonic controls, with periodicity often difficult to measure precisely.

Article

Stratigraphic Cycles: What Are They? is a general/educational published by Geological Digressions in 2024. It presents an accessible overview explaining that stratigraphic cycles occur at scales from millimetres to hundreds of metres thick, driven by sea-level, sediment supply, and tectonic controls, with periodicity often difficult to measure precisely.

General overview, notes periodicities are hard to measure especially below biostratigraphic/radiometric resolution. It also considers example of 5 shale-sandstone cycles over ~35m outcrop. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: All these cycles have periodicities, although measuring them continues to be a problem for stratigraphers, particularly those of durations less than the resolution of biostratigraphic or radiometric measures of age. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together stratigraphic cycles, sequence stratigraphy, sea-level change, sediment supply. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because this is a general/educational, it is best used as an accessible introduction or perspective rather than as conclusive evidence. Forum discussion should follow its references back to the primary data and original research wherever possible.

Source details and credits

• Source / publisher: Geological Digressions
• Source type: General/educational
• URL type: WWW
• Credits: Geological Digressions
• URL: https://www.geological-digressions.com/stratigraphic-cycles-what-are-they/

First published: 2021

Brief summary

Historical and conceptual review of cyclicity thinking in stratigraphy, tracing ideas from Eduard Suess and Barrell's diastem concept through to modern orbital-cyclicity-based stratigraphic methods.

Article

Cycles in Earth Sciences, Quo Vadis? Essay on Cyclicity Concepts is a peer-reviewed journal article published by History of Geo- and Space Sciences (Copernicus) in 2021. It focuses on historical and conceptual review of cyclicity thinking in stratigraphy, tracing ideas from Eduard Suess and Barrell's diastem concept through to modern orbital-cyclicity-based stratigraphic methods.

Conceptual/historical review rather than a single measured period. It also considers covers base-level cyclicity and orbital forcing concepts used to interpret stratigraphic record. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: Current stratigraphic research integrates several methods to identify repetitive patterns in the stratigraphic record and to interpret oscillatory geological processes; Barrell pioneered understanding of cyclic erosion and accumulation processes. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together earth science cycles, stratigraphic cyclicity, orbital forcing, history of geology. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a peer-reviewed journal article, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: History of Geo- and Space Sciences (Copernicus)
• Source type: Peer-reviewed journal article
• URL type: PDF
• Credits: History of Geo- and Space Sciences (Copernicus)
• URL: https://hgss.copernicus.org/preprints/hgss-2021-21/hgss-2021-21.pdf

First published: 2020

Brief summary

Meta-review of 58 published spectral analyses of impact crater ages and 35 analyses of extinction events; finds a majority support significant cycles averaging ~29.7 Myr (craters) and ~26.5 Myr (extinctions), with mutual ~26 Myr phase alignment.

Article

Are Impact Craters and Extinction Episodes Periodic? Implications for Planetary Science and Astrobiology is a peer-reviewed review article published by Astrobiology (journal) in 2020. It focuses on meta-review of 58 published spectral analyses of impact crater ages and 35 analyses of extinction events; finds a majority support significant cycles averaging ~29.7 Myr (craters) and ~26.5 Myr (extinctions), with mutual ~26 Myr phase alignment.

The analysis focuses on ~29.7 Myr (craters, ~60% of 58 analyses significant), ~26.5 Myr (extinctions, ~67% of 35 analyses significant). It also considers cross-wavelet transform analysis used. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: About 60% of the crater trials support a statistically significant cycle averaging approximately 29.7 million years, and about 67% of the trials of extinction episodes found a significant cycle averaging approximately 26.5 million years. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together impact craters, extinction cycles, astrobiology, meta-analysis. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a peer-reviewed review article, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: Astrobiology (journal)
• Source type: Peer-reviewed review article
• URL type: WWW
• Credits: Astrobiology (journal)
• URL: https://pubmed.ncbi.nlm.nih.gov/32865423/

First published: 2020

Brief summary

News coverage of a study finding that mass extinctions of land animals follow the same ~26-27 million year cycle already known from marine extinctions, coinciding with major impact and flood-basalt volcanism events.

Article

Mass Extinctions of Land-Dwelling Animals Occur in 27-Million-Year Cycle is a science news summary of peer-reviewed study published by ScienceDaily (reporting NYU/Rampino study) in 2020. It presents a news coverage of a study finding that mass extinctions of land animals follow the same ~26-27 million year cycle already known from marine extinctions, coinciding with major impact and flood-basalt volcanism events.

The analysis focuses on 26-27 million years. It also considers ties together land extinction, marine extinction, impact crater, and flood-basalt volcanism records. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: These new findings of coinciding, sudden mass extinctions on land and in the oceans, and of the common 26- to 27-million-year cycle, lend credence to the idea of periodic global catastrophic events as triggers for the extinctions. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together land animal extinctions, 27-million-year cycle, mass extinctions, flood-basalt volcanism. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a science news summary of peer-reviewed study, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: ScienceDaily (reporting NYU/Rampino study)
• Source type: Science news summary of peer-reviewed study
• URL type: WWW
• Credits: ScienceDaily (reporting NYU/Rampino study)
• URL: https://www.sciencedaily.com/releases/2020/12/201211083113.htm

First published: 2015

Brief summary

Circular spectral analysis of 37 dated impact craters and marine extinction events over 260 Myr finds statistically significant cycles of 25.8±0.6 Myr (craters) and 27.0±0.7 Myr (extinctions), in common phase.

Article

Periodic Impact Cratering and Extinction Events Over the Last 260 Million Years is a peer-reviewed journal article published by Monthly Notices of the Royal Astronomical Society (Oxford) in 2015. It focuses on circular spectral analysis of 37 dated impact craters and marine extinction events over 260 Myr finds statistically significant cycles of 25.8±0.6 Myr (craters) and 27.0±0.7 Myr (extinctions), in common phase.

The analysis focuses on 25.8 ± 0.6 Myr (craters), 27.0 ± 0.7 Myr (extinctions). The data source is 37 well-dated craters + 8 marine extinction events, redated to Gradstein et al. 2012 timescale. This gives the cycle claim a specific numerical and evidential setting rather than presenting periodicity only as a visual impression.

The article reports the following result: A digital circular spectral analysis of 37 crater ages yielded evidence for a significant 25.8 ± 0.6 Myr cycle, and using the same method a significant 27.0 ± 0.7 Myr cycle was found in the dates of eight recognised marine extinction events. The interpretation is strongest when it survives dating uncertainty, preservation bias, alternative event selections and correction for multiple statistical tests.

For cycles researchers, the article brings together impact cratering cycles, extinction periodicity, circular spectral analysis, 26-million-year cycle. It is relevant to debates over whether recurring patterns in the geological record reflect astronomical forcing, internal Earth processes, preservation bias or dating uncertainty.

Because it is a peer-reviewed journal article, the article is a strong starting point for discussion in the Geology & Paleontology forum, although its conclusions should still be compared with later replications and updated datasets.

Source details and credits

• Source / publisher: Monthly Notices of the Royal Astronomical Society (Oxford)
• Source type: Peer-reviewed journal article
• URL type: WWW
• Credits: Monthly Notices of the Royal Astronomical Society (Oxford)
• URL: https://academic.oup.com/mnras/article/454/4/3480/992970