Astronomy Meets Climate

A 100,000 year climate cycle on Earth can be explained by Earth's orbit.

The 100,000-year problem concerns the dominant period of glacial-interglacial cycles over the past 800,000 years and their correlation with Earth's orbital eccentricity, despite eccentricity's weak influence on solar radiation. 

Two theories compete: the astronomical theory, in which orbital forcing drives the cycles with amplification from Earth system feedbacks, and the geochemical theory, in which internal dynamics dominate with orbital forcing synchronising oscillations. We investigate these theories using conceptual models. 

Augmentations to the Budyko energy balance model fail to reproduce the 100,000-year period, revealing formulation limitations. Linearised versions of existing non-linear ice volume models perform comparably to their full counterparts, indicating the data does not necessitate non-linear dynamics. We develop two simple linear models: a feedforward model aligned with the astronomical theory and a feedback model aligned with the geochemical theory. 

The feedforward model reproduces the ice volume record well and offers a novel explanation for the absence of eccentricity's 400,000-year period, arising from oceanic heat storage and tropospheric energy responding with differing phase lags. Conservative estimates show bulk ocean temperature variation can be explained by eccentricity alone, challenging the geochemical theory's core assumption. 

We also show that widespread use of Q65 may bias models towards geochemical explanations by underrepresenting eccentricity. The feedback model's improvement is concentrated around Marine Isotope Stage 11, suggesting this anomalous interglacial reflects Earth-based events rather than a general requirement for feedback mechanisms. We conclude that 800,000 years of glacial cycles can be largely reproduced by a linear astronomical model, emphasising the importance of parsimony when interpreting palaeoclimate data.

Liam Wheen, "A First Principles Approach to the 100,000-year Problem" arXiv:2604.12143 (April 14, 2026).

Quick Hits

* The Sumerians had different number words and symbols to count numbers of different kinds of things. So, for example, the word for five pieces of fruit would be different than the word for five logs.

* Egyptian pyramids were built as trapezoids and then cut down to pyramids with the left over rock used to make new pyramids.

* Reputedly, Emperor Basil II of the Byzantine Empire was cruel.

* The Anglo-Saxons kept slaves in the middle ages.

* According to Gerald of Wales ca. 1316 CE, at that time the Irish were predominantly herders.

* Harsh murder sentences for newborns killed or neglected in the throes of unattended child birth are still common today even though the death penalty is almost never sought now in these circumstances.

* The TYRP1 gene variant discovered in 2012, is the cause of blond hair in the Solomon Islands in Melanesia, which is a different gene than the one that causes blond hair in Europeans.

* Before 1480, India and Sri Lanka were nearly connected by a land bridge known as Adam’s Bridge.

* There were once oceans on Mars.

High-resolution orbital images of Mars' largest canyon reveal ancient river deltas, proving the Red Planet once held an ocean the size of Earth's Arctic.

New high-resolution imagery from the European Space Agency’s ExoMars Trace Gas Orbiter has provided the most definitive evidence to date that Mars was once a blue planet. Researchers at the University of Bern identified distinct fan-shaped sediment deposits in the southeast Coprates Chasma region, part of the massive Valles Marineris canyon system. These structures, remarkably similar to river deltas on Earth, all sit at a consistent elevation between 3,650 and 3,750 meters. This geological alignment points to one unmistakable conclusion: the presence of an ancient coastline where rivers once emptied into a vast, stable sea approximately 3.37 billion years ago.

While previous theories about Martian oceans relied on lower-resolution data, this study offers direct geomorphological proof of a shoreline. The findings suggest that a massive body of water, comparable in size to Earth’s Arctic Ocean, once covered the entirety of Mars’ northern hemisphere. Though today these ancient deltas are buried beneath wind-sculpted dust and dunes, their distinctive shapes remain preserved. This discovery drastically alters our view of Martian history; the existence of a planet-wide water cycle and a stable ocean suggests that the conditions necessary for life were not isolated occurrences but a global phenomenon.

Source: Argadestya, P., et al. "Geomorphological and sedimentological evidence of a coastline in Southeast Coprates Chasma." npj Space Exploration (2026).

* There are social octopi that build homes for themselves off the coast of Australia.

* This very little bugger ,who is part of this clade of animals (and more specifically this one) is kind of cute in a Disney monsters way. They are the most heat-tolerant complex animal known to science after tardigrades (or water bears), which are able to survive temperatures over 150 °C. They were discovered in 1980 off the Galapagos islands.

When they grow up, they look like this (the "fur" is a symbiotic species of bacteria):

* A photograph of the February 19, 2026 solar eclipse in Antarctica (not AI).

* Nature can be amazing (also not AI).

* In West Texas, ca. 4500 BCE, hunter-gatherers used non-returnable boomerang sticks for small game and atlatl to throw their carefully crafted spears further for big game.

A cache of ancient weapons, more than 6,000 years old, has been uncovered in a remote rock shelter in West Texas, offering one of the clearest pictures yet of early life in North America.

The discovery was made at the San Esteban rock shelter in the Big Bend region, an area known for its dry climate and rugged desert landscape. That dryness turned out to be a gift to archaeologists. Items that would normally rot away wood, leather bindings, plant fibers remained intact for thousands of years. Inside the shelter, researchers found a carefully stored hunting kit dating to around 4,500 B.C., including wooden spear shafts wrapped in leather, stone projectile points, and parts of atlatls, the spear-throwing tools that dramatically increased a hunter’s range and power.

An atlatl works like a lever, giving a thrown spear greater speed and force. With it, hunters could strike animals from distances that would otherwise be impossible with a simple hand throw. Tests and prior studies show these tools could send projectiles well over 100 feet with deadly accuracy. The craftsmanship seen in the newly uncovered pieces shows careful shaping, balance, and planning. These were not rough survival tools; they were refined hunting systems built by people who deeply understood their environment.

Researchers also identified curved wooden throwing weapons often described as straight or non-returning boomerangs. Unlike the returning boomerangs many people picture today, these were designed to fly straight and hit small game with strong impact. Their presence adds another layer to what appears to have been a well-organized toolkit, likely stored together for repeated use.

The San Esteban site has a long history of human occupation stretching back thousands of years. Findings from this latest excavation reinforce the idea that the Big Bend region was not a temporary stop for wandering groups but a place where people lived, adapted, and developed sophisticated survival strategies. The tools show planning, skill, and an ability to work with available materials in smart, efficient ways.

Archaeologists involved in the project say the discovery helps rewrite outdated ideas about early North American societies. These communities were not primitive in the way older textbooks sometimes suggested. They engineered effective hunting technology, understood animal behavior, and created tools built to last.

As research continues, scientists hope to learn more about how these weapons were used, how they were stored, and what they reveal about daily life 6,000 years ago. For now, the dry rock shelter in West Texas has delivered something rare: a direct, tangible connection to hunters who once stood in the same desert landscape, preparing their tools for the next expedition.

* Maize farmers in Peru’s Chincha Valley were fertilizing their crops with seabird poop as early as the year 1250 CE.

* According to this source:

Around 3,800 years ago, a magnitude-9.5 megaquake struck northern Chile's coast, creating the largest earthquake known in human history. The rupture extended roughly 620 miles along the fault line—longer than the devastating 1960 Valdivia earthquake—and generated tsunamis with waves reaching 66 feet that traveled 5,000 miles across the Pacific Ocean to New Zealand. Archaeologists discovered marine deposits, boulders, shells, and sea life displaced far inland in the Atacama Desert, along with toppled stone structures buried beneath tsunami sediment, all radiocarbon-dated to this single catastrophic event.

The disaster forced complete coastal abandonment. Communities that depended on the ocean for survival relocated inland, staying away from the coast for over 1,000 years—an extraordinary response that demonstrates the quake's devastating impact on human populations. Researchers now recognize this megathrust earthquake, caused when tectonic plates suddenly unlocked after building massive strain, as both the oldest discovered earthquake-tsunami disaster in the Southern Hemisphere and a critical warning for modern coastal populations across the Pacific.

* Every recorded earthquake worldwide, 2015 to 2025 (my source didn't cite a source).

 

The Amazon Is Older Than The Andes

 The fascinating deep history of the Amazon River.

How Did The Depression In The Indian Ocean Arise?

There is a hundred meter deep dimple in the middle of the Indian Ocean discovered in 1948. It is officially called the "Indian Ocean geoid low." Proximately, it exists because the density of the planet there is different than it is in adjacent places causing gravity in its vicinity to be weaker.

Scientists think may be related to a magma plume that arose 20 million years ago or so when the ocean between the Indian subcontinent collided with Asia as continent drift sent it moving North. But, this theory for how it formed, tested in simulations, isn't a perfect fit the data:

[I]t completely fails to reproduce the powerful mantle dynamic plume that erupted 65 million years ago under the present-day location of Réunion Island,” he said. “The eruption of lava flows that covered half of the Indian subcontinent at this time — producing the celebrated Deccan Traps, one of the largest volcanic features on Earth — have long been attributed to a powerful mantle plume that is completely absent from the model simulation.”

Another issue, Forte added, is the difference between the geoid, or surface shape, predicted by the computer simulation and the actual one: “These differences are especially noticeable in the Pacific Ocean, Africa and Eurasia. The authors mention that there is a moderate correlation, around 80%, between the predicted and observed geoids, but they don’t provide a more precise measure of how well they match numerically (in the study). This mismatch suggests that there may be some deficiencies in the computer simulation.”

The paper and its introductory summaries are as follows:

Abstract

The origin of the Earth's lowest geoid, the Indian Ocean geoid low (IOGL) has been controversial. The geoid predicted from present-day tomography models has shown that mid to upper mantle hot anomalies are integral in generating the IOGL. Here we assimilate plate reconstruction in global mantle convection models starting from 140 Ma and show that sinking Tethyan slabs perturbed the African Large Low Shear Velocity province and generated plumes beneath the Indian Ocean, which led to the formation of this negative geoid anomaly. We also show that this low can be reproduced by surrounding mantle density anomalies, without having them present directly beneath the geoid low. We tune the density and viscosity of thermochemical piles at core-mantle boundary, Clapeyron slope and density jump at 660 km discontinuity, and the strength of slabs, to control the rise of plumes, which in turn determine the shape and amplitude of the geoid low. 

Key Points

* Employing time dependent global mantle convection models since the Cretaceous we simulate the origin of the enigmatic Indian Ocean geoid low

* Plumes forming along the edges of the African Large Low Shear Velocity province (LLSVP) control the regional geoid in the Indian Ocean

* These plumes, in turn are generated by lower mantle Tethyan slabs that perturb the African LLSVP

Plain Language Summary

The origin of the deepest geoid on Earth, the Indian Ocean geoid low (IOGL), is debated. Several competing hypotheses exist, amongst which, a recent study employing tomography models suggested that hot anomalies at mid to upper mantle depths are crucial in generating this elusive feature. Assimilating plate motion in global mantle convection models from the Mesozoic till the present day, we attempt to trace the formation of this geoid low. We show that flow induced by downwelling Tethys slabs perturbs the African Large Low Shear Velocity province and gives rise to plumes that reach the upper mantle. These plumes, along with the mantle structure in the vicinity of the geoid low, are responsible for the formation of this negative geoid anomaly. Exploring a wide model parameter space, such as the density and intrinsic viscosity of the thermochemical piles, Clapeyron slope and density jump at 660 km depth, strength of slabs, we show that plumes are integral in generating the IOGL. The contribution of lower mantle Tethys slabs is secondary but also necessary in generating this geoid low.

Debanjan Pal, Attreyee Ghosh, "How the Indian Ocean Geoid Low Was Formed" Geophysical Research Letters (May 5, 2023). 

We don't know everything. One of the things we are continuing to deepen our understanding of are the details of our own planet's composition and inner structure. Improvements in sophisticated geo-sensors and the computational power necessary to run models of how the geology has evolved over time are giving us better answers to these questions. 

A Long, Long Time Ago, On Earth

 The names are obviously anachronistic.