Past and future Milankovitch cycles via VSOP model Graphic shows variations in five orbital elements: Axial tilt or obliquity (ε). Eccentricity (e). Longitude of perihelion (sin(ϖ)). Precession index (e sin(ϖ)) Precession index and obliquity control insolation at each latitude: Daily-average insolation at top of atmosphere on summer solstice () at 65° N Ocean sediment and Antarctic ice strata record ancient sea levels and temperatures: Benthic forams (57 widespread locations) Vostok ice core (Antarctica) Vertical gray line shows present (2000 CE)
Another awkward chapter in Earth's history has emerged from the darkness of Peruvian caves — and it stretches back some 450,000 years. For young-Earth creationists, that is an inconvenient amount of climate history to squeeze into a universe supposedly created only a few thousand years ago. For scientists, it is an opportunity to investigate how the rainfall systems on which ecosystems and human societies depend respond to a changing planet.
The research, published in Nature was led by Elizabeth Olson, a former postdoctoral researcher at Union who is now at Wesleyan University. The team examined stalagmites from caves in the Peruvian Andes, using their chemical composition to reconstruct the history of the South American summer monsoon. The resulting record has an average resolution of about 50 years, providing an unusually detailed view of changes across several glacial–interglacial cycles.
Stalagmites grow upwards as dripping water deposits minerals on cave floors. As they accumulate, their layers can preserve changes in oxygen-isotope composition that reflect the climatic history of the water reaching the cave. Uranium–thorium dating provides the chronology, while the oxygen isotopes provide evidence of past monsoon behaviour. These are complementary measurements: the researchers are reading a dated chemical archive, not simply assuming that every stalagmite grows at a constant rate.
Location of caves where speleothems were recovered.
Credit:Olson, E.J., et al (2026)
Some of those departures involved prolonged weakening of monsoons in both hemispheres. That matters because a rainfall system can sustain abundant life without being a guaranteed, permanently reliable water supply. The evidence describes a dynamic Earth whose climate responds to physical conditions, sometimes with disruptive consequences. It gives little comfort to the claim that our surroundings were perfectly arranged to ensure human wellbeing.
The chronological problem for biblical literalism is more direct still. A reconstruction extending across approximately 450,000 years reaches back roughly 75 times further than the familiar 6,000-year creationist chronology permits. The challenge is not merely to explain how mineral formations can grow, but to account for their dated chemical histories and the relationships between climate records on different continents. Once again, researchers investigating how the real world works have produced evidence profoundly incompatible with a literal reading of Genesis — without needing to make creationism the subject of their research.
Background^ Milankovitch Cycles — Earth's Changing Orbital Rhythms. Milankovitch cycles are long-term changes in Earth's orbit and the orientation of its rotational axis. Named after the Serbian mathematician Milutin Milankovitch, who calculated their climatic effects, they alter the distribution of sunlight between seasons and latitudes. Their main climatic importance is therefore where and when solar energy arrives, rather than a large change in the total energy Earth receives each year.The research published in Nature is also described in a Union College news report:
Why does Earth's orbit change? Earth does not orbit an isolated Sun. Every planet exerts gravitational forces on the others, gradually changing the shapes and orientations of their orbits. These interactions produce overlapping, approximately repeating variations rather than one perfectly regular cycle. Jupiter and Saturn are particularly influential because of their enormous masses.
Earth's spin axis also responds to gravity. Rotation gives our planet a slight equatorial bulge, on which the Sun and Moon exert a gravitational turning force. Like a spinning top responding to gravity, Earth changes the direction of its axis. Meanwhile, planetary perturbations change the orientation of Earth's orbital plane. Together, these movements alter the relationship between its axis and its orbit.
The three main components
- Eccentricity — changes in orbital shape. Earth's orbit varies between almost circular and slightly more elliptical. Important variations occur on timescales of approximately 100,000 years, with a prominent longer cycle of about 405,000 years. Greater eccentricity increases the difference between Earth's nearest and furthest distances from the Sun, strengthening the seasonal effects of precession.
- Obliquity — changes in axial tilt. Earth's axis varies between approximately 22.1° and 24.5° from the perpendicular to its orbital plane, over about 41,000 years. Greater tilt increases seasonal contrasts, especially at high latitudes. Reduced tilt produces cooler high-latitude summers, helping winter snow survive and ice sheets accumulate.
- Precession — changes in the direction of the axis. Earth's axis traces a slow circle relative to the stars in approximately 26,000 years. The orbital ellipse itself also turns. Together, these movements produce climatic precession cycles of roughly 19,000–23,000 years, changing whether a hemisphere's summer occurs nearer Earth's closest approach to the Sun or its greatest distance from it.
A useful distinction: Earth's axial tilt causes the annual seasons. Milankovitch cycles slowly modify their intensity and their relationship to Earth's position along its orbit.
How do these cycles affect climate? Summer conditions are particularly important for ice sheets. A cold winter can deliver abundant snow, but whether that snow survives depends on the following summer. If successive summers leave some snow unmelted, ice can accumulate. Expanding snow and ice then reflect more sunlight, amplifying the initial cooling. Changes in greenhouse gases and ocean circulation can further modify the response.
Monsoons also respond to changes in seasonal heating and atmospheric circulation. Precession can favour stronger summer heating in one hemisphere while reducing it in the other, helping explain why Asian and South American monsoon records often show opposing trends. However, ice sheets, greenhouse gases and ocean temperatures also influence rainfall, so the monsoons do not follow a simple astronomical timetable.
How do scientists test the explanation? Astronomical calculations predict changes in sunlight through time. Scientists compare those predictions with climate evidence preserved in marine sediments, ice cores and cave deposits. In the Peruvian study, uranium–thorium dates establish the stalagmites' chronology, while oxygen isotopes provide evidence of past monsoon behaviour. Agreement between these different kinds of evidence makes the explanation testable.
The resulting picture is of a planet governed by interacting physical processes across tens and hundreds of thousands of years. Even one of the shorter climatic precession cycles lasts several times longer than the entire history allowed by a conventional young-Earth creationist chronology.
Peruvian caves sound the alarm for global long-term drought, a team of researchers at Union discover
Caves in the tropical Peruvian Andes hold clues amassed over the past 450,000 years, which suggest a strong possibility for an alarming reduction in rainfall across a third of the globe, according to a new study.
The long-term drought is a troubling issue for the more than 2.7 billion people on Earth who depend on monsoon rains for fresh water.
The research was published this week in Nature, the world’s leading journal of peer-reviewed science research.
Elizabeth Olson, a former post-doctoral researcher in geosciences at Union, collecting drip waters inside Haugapo cave in the Peruvian Andes. Now a visiting professor of earth and environmental sciences at Wesleyan University, Olson is the lead author of new study that shows caves in the tropical Peruvian Andes hold clues amassed over the past 450,000 years which suggest a strong possibility for an alarming reduction in rainfall across a third of the globe. The research was published this week in Nature, the world’s leading journal of peer-reviewed science research.
The article is exciting because it provides scientists with a half-million-year rainfall history for most of the South American continent. The future of freshwater resources is increasingly uncertain as the human population grows and weather patterns shift in response to the changing climate. This record is very high-resolution, with an average resolution of 50 years. That resolution let us investigate changes between the South American and Asian monsoons at a scale that has never been accessible before.
Professor Elizabeth J. Olson, lead author.
Formerly - Union College, Schenectady, NY, USA.
Now - Wesleyan University, Connecticut, USA.
Caves in the tropical Peruvian Andes hold clues amassed over the past 450,000 years, which suggest a strong possibility for an alarming reduction in rainfall across a third of the globe, according to a new study. The long-term drought is a troubling issue for the more than 2.7 billion people on Earth who depend on monsoon rains for fresh water.
Elizabeth Olson, a former post-doctoral researcher in geosciences at Union, collecting drip waters inside Haugapo cave in the Peruvian Andes. Now a visiting professor of earth and environmental sciences at Wesleyan University, Olson is the lead author of new study that shows caves in the tropical Peruvian Andes hold clues amassed over the past 450,000 years which suggest a strong possibility for an alarming reduction in rainfall across a third of the globe. The research was published this week in Nature, the world’s leading journal of peer-reviewed science research.
Researchers spent six years examining cave stalagmites – mineral formations created by water dripping onto cave floors – to determine monsoon strength. Monsoon rainfall is the primary fresh water source for Earth’s most diverse ecosystems and for much of the Earth’s population.
Researchers sampled rainwater, cave drip water, air and rocks to determine the seasonality of stalagmite formation. At Union’s Stable Isotope Laboratory, they analyzed the samples’ isotopic composition to reconstruct monsoon strength over time. They discovered that the global monsoon system has periodically oscillated, strengthening in one hemisphere while weaking in the other. However, during intervals of warmth and warming climate, monsoons in both hemispheres failed for millennia.
These instances of monsoon systems collapsing in both hemispheres during intervals of natural warming are alarming, the study asserts, raising the likelihood of long-term drought.
The Southern and Northern Hemisphere monsoons are normally out of phase with each other but the record shows that there were times in the past when this was not the case. This means that there is a gap in our understanding of how these important systems work. In the article, we explore what might have caused that behavior. But this work has opened up a research area that will be explored for decades to come.
Professor Elizabeth J. Olson.
Co-authors include David Gillikin, the William D. Williams Professor of Geosciences and chair of the department; Osamu Miyawaki, assistant professor of geosciences; Laura Piccirillo ’20, a Ph.D. student at Duke; Donald Rodbell, the Jane and John Wold Professor of Geosciences; and Anouk Verheyden-Gillikin, senior lecturer in geosciences.
David Gillikin, the William D. Williams Professor of Geosciences and chair of the department, and Donald Rodbell, the Jane and John Wold Professor of Geosciences, with students Patrik O’Brien ’27, Lucy Andersen ’27, Sophia Gomes ’27 and Bess DiNorcia ’28 deep inside Pacupahuain cave in the Peruvian Andes.
In addition, the research was built on the senior thesis projects of 16 Union students over the past six years.
This is a prime example of how paleoclimatology can shed light on our climate future. Studying how the world has responded to warming episodes in Earth's distant past can inform us about what we might expect in our future. It is especially gratifying that so many of my colleagues in the Geoscience Department collaborated on this work, and that so many students participated through their senior thesis research projects.
Professor Donal T. Rodbell, co-author
Union College
Schenectady, NY, USA.
The latest research highlighted in Nature is part of an ongoing project, led by Rodbell and Gillikin, to develop the longest continuous paleoclimate record from the region known as the “heat engine” of Earth. Researchers are collecting lake sediments and cave deposits from the tropical Andes of Central Peru that hold important data about the Earth’s climate history and suggest what the future may hold.
Publication:
Once again, scientists investigating an aspect of the natural world have produced evidence that incidentally demolishes the young-Earth creationist chronology. These stalagmites preserve a climate history extending back approximately 450,000 years, with changes that can be compared with records from another continent and understood in the context of Earth's orbital cycles. This is not simply a question of accepting an inconvenient date: it is a question of explaining the agreement between radiometric dating, cave chemistry, climate records and celestial mechanics.
The planet revealed by this research is also far removed from the reassuring picture of an environment perfectly arranged for human welfare. Rainfall systems respond to changing seasonal sunlight, ocean temperatures, greenhouse gases and ice cover. They can shift substantially, and the usual relationship between monsoons in opposite hemispheres can break down. A world capable of supporting human life is plainly not the same thing as a world engineered to guarantee its inhabitants reliable water supplies.
Nor does the discovery that the monsoons sometimes departed from their usual pattern undermine the scientific explanation. Those departures are precisely what make the findings valuable: they reveal where a simple account is insufficient and identify further processes that researchers need to investigate. Science advances by examining such complications and revising its models accordingly. Biblical literalism, by contrast, requires the evidence to accommodate a chronology fixed before the investigation begins.
The researchers did not need to invoke supernatural intervention to explain the record, nor did they need to set out to refute Genesis. They asked how Earth's climate behaved, measured the evidence and compared competing physical explanations. The embarrassment for creationism arises because the answers describe a real history that its preferred story cannot accommodate.
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