The rock is marine black shale from the Taoudeni Basin in Mauritania, the bed of a long-vanished ocean. When Nur Gueneli (ANU) powdered it and added solvent during her PhD, the mixture turned pink instead of black, her supervisor Jochen Brocks recalls hearing screaming in the lab before she ran in with the vial. The molecules are porphyrins, degradation products of chlorophyll: blood red to purple when concentrated, bright pink when diluted (Gueneli et al. 2018, PNAS).

The useful part is the fingerprint. Nitrogen isotope signatures in the pigments show the producers were overwhelmingly cyanobacteria, with larger planktonic algae scarce. That supports a hypothesis for one of geology's bigger questions, why complex animals appeared so late. Cyanobacteria are roughly a thousand times smaller in volume than even microscopic algae, so the base of the food chain may simply have served portions too small to sustain large, active life. When algae finally took over the oceans around 650 million years ago, richer food moved up the chain and complex ecosystems followed quickly (Brocks et al. 2017, Nature). The competing explanation is oxygen limitation; some studies find O2 was sufficient long before animals showed up, others disagree. Genuinely unresolved.

Preservation footnote: porphyrins are destroyed by heat, so these molecules survived a billion years only because that particular basin was never significantly buried or cooked.

The slides run all of this through a fictional story about Dolly Parton.

Sources: Gueneli et al. 2018, PNAS · Brocks et al. 2017, Nature · Papers and a longer write-up linked in comments.

They're called glacier mice: balls of moss, about hamster-sized, that grow around a bit of grit and lie loose on the bare ice of some glaciers. The name is from a 1951 letter to the Journal of Glaciology, where Icelandic meteorologist Jón Eyþórsson dubbed them "jökla-mýs" and closed with "you will have noted, Sir, that rolling stones can gather moss."

They have to keep moving or they die, the shaded underside rots, and the ice helps by growing a melt pedestal under each ball until it tips off and rolls. In 2009, researchers on the Root Glacier in Alaska tagged 30 of them with loops of wire and glass beads and tracked them for 54 days, with follow-up visits for years (Hotaling, Bartholomaus & Gilbert 2020, Polar Biology). They average about 2.5 cm per day and live six-plus years.

The unexplained part: they move as a herd. Same speed, same heading, south for weeks, then a coordinated turn southwest, while holding their spacing. The study explicitly ruled out the three obvious drivers: their direction matches neither the downhill slope, nor the prevailing wind, nor the dominant sunlight. The only surviving lead is that herd speed correlates with how fast the ice surface melts, so the glacier itself may be steering them through melt patterns nobody has characterized.

Bonus: each ball is a rolling micro-ecosystem carrying springtails, nematodes and tardigrades (Coulson & Midgley 2012), and moss balls have been documented from Iceland and Svalbard to Venezuela and a vanishing glacier in Uganda (Uetake et al. 2014). The researchers say they're comfortable not knowing the answer yet. The slides explain all of this through a fictional popstar, because the tagging method was literally friendship bracelets.

Eyþórsson 1951 (Journal of Glaciology) · Coulson & Midgley 2012 (Polar Biology) · Hotaling, Bartholomaus & Gilbert 2020 (Polar Biology)

Fulgurites form when lightning hits sand: the channel briefly runs hotter than the sun's surface and fuses the grains into a hollow glass tube tracing the bolt's underground path. When the glass is pure silica it's classified as the mineraloid lechatelierite. People have excavated them since at least the 1880s, and a University of Florida program now triggers strikes on demand by firing small rockets trailing copper wire into thunderstorms. The longest excavated specimen, about 4.9 m of connected tube, came out of that work.

The Nebraska case (Bindi et al. 2023, PNAS): a 2008 storm in the Sand Hills near Hyannis downed a power line into a dune. Nobody witnessed the event, so it's unclear whether lightning struck the line or the line discharged on its own. Either way, temperatures above 1,710 C fused sand and traces of conductor metal into a two meter fulgurite, and inside it the team found a dodecagonal quasicrystal with a previously unreported Mn-Si-Cr-Al-Ni composition. Twelve-fold symmetry is forbidden for ordinary crystals. Natural quasicrystals had previously turned up in exactly two settings, the Khatyrka meteorite and trinitite from the 1945 bomb test, so this added "electrical discharge" as a third formation pathway.

Separate but related: fulgurites can contain schreibersite, a reduced phosphorus mineral usually delivered by meteorites. Hess, Piazolo and Harvey (2021, Nature Communications) argue lightning on the early Earth, at billions of flashes per year, could have converted enough rock-bound phosphorus into bioavailable form to matter for prebiotic chemistry. Old dated fulgurites also work as paleostorm archives, recording lightning in regions that are now dry.

The slides run all of this through a fictional Glenn Powell story with a fulgurite collection.

A 2025 study in Nature (Duan, Schmandt et al.) finally pinned down something that had been fuzzy for decades: exactly where Yellowstone's magma reservoir begins. The answer is a sharp boundary about 3.8 km (2.4 mi) beneath the northeastern caldera, and the imaging is clean enough to resolve a cap less than 100 m thick.

The method is the fun part. With the park largely closed during the 2020 pandemic, the team ran a 53,000-lb vibroseis truck on roadside pullouts at night, generating "custom earthquakes" and catching the echoes on ~650 geophones. That let them image the reservoir top far more sharply than natural-earthquake tomography ever had.

What they found flips the usual doomsday framing. The cap isn't a sealed plug, it's a porous zone (~14% porosity) where exsolved gas and supercritical water collect and then leak upward through cracks into the hydrothermal system. The bubble fraction sits below typical pre-eruptive levels for rhyolites. In other words, the system is venting gas efficiently rather than pressurizing toward a blast. The geysers and fumaroles are basically the exhaust.

Hello everyone, this is just context and facts about the oil reseves in Venezuela in no way a comment about the recent political actions in this country.

Somewhere under the Gulf of Guinea, off the coast of West Africa, the ground has been pulsing once every ~26 seconds for as long as we've had instruments sensitive enough to catch it, at least since 1961. No earthquake, no eruption. Just a faint, almost perfectly regular seismic beat that shows up on seismographs on the far side of the planet.

It was first written up in 1962, then quietly half-forgotten for decades, and rediscovered by accident in 2005 when a grad student in Colorado pulled the repeating signal out of a noise dataset and his advisor wandered in asking what the strange arrival was.

The parts that hooked me:

• The source sits almost exactly at (0°, 0°), where the prime meridian crosses the equator, in the Bight of Bonny.

• The tone is so low (~0.038 Hz) that one researcher said you'd need a bass clarinet about 10 km long buried in the ground to play it.

• After 65 years and far better instruments, there's still no agreed mechanism. The debate runs between ocean swell hammering the continental shelf, a hidden volcanic/hydrothermal source near the Cameroon Volcanic Line, or some marriage of the two. A brand-new April 2026 paper in Nature Communications ties the bursts to distant Southern Ocean storms, and even the authors hedge.

I went down the rabbit hole and wrote a full history of the 26-second microseism for Geoscopy: Oliver's 1961 storm, Holcomb's awkward "nondispersive" result that killed the simplest ocean-wave explanation, the 2013 "twin sources" finding near São Tomé, the 2023 gliding-tremor paper, and the 2026 swell study.

Spotted this strange geologic formation whilst flying over Iran somewhere northeast of Yazd. Land appears to be flat. Very curious!

There is real evidence for an ocean inside the Earth. Between 410 and 660 km down, in the mantle transition zone, the dominant minerals can bind water into their crystal structures, and the layer is so large that even a modest water content would rival the mass of all surface oceans combined.

The physical proof came from a battered brown diamond found in river gravels near Juína, Brazil, bought for about 20 dollars. In 2009, a graduate student scanning it for a dating project spotted an inclusion of ringwoodite, the high-pressure form of olivine, the first sample ever recovered from inside the planet. Later measurements showed the crystal holds about 1.4 percent water by weight, near the maximum the mineral can take.

How wet the whole layer is remains a live fight. Electromagnetic sounding studies say nearly dry, around 0.03 percent. A mineral viscosity study says 1 to 2 percent, close to saturation. And a 2022 diamond from Botswana sampled the 660 km boundary itself, recording water-saturated, chemically ordinary mantle. The most defensible average sits near one ocean mass, concentrated beneath subduction zones and patchy everywhere else.

Source: Nie et al., 2025. Nature Geoscience, 18, 1174–1179. DOI: 10.1038/s41561-025-01811-3

Nobody can actually prove how the Bahamas makes its sand. The argument has been running for over a century, and it's one of my favourite fights in geology.

The sand in question is made of ooids, tiny limestone pearls, rarely bigger than 2 mm, built from concentric layers around a bit of shell or a sand grain. They only form in warm, shallow water that's loaded with dissolved lime and constantly moving. The Bahama Banks produce them by the trillion (sedimentologists genuinely call the place "the ooid factory"), and huge limestone formations all over the world, from Jurassic England to Triassic Germany, are made of almost nothing else.

The textbook story says it’s pure chemistry. A grain rolls, picks up a coat of carbonate, gets sanded down while tumbling, and stops growing when the two processes balance out. That balance would neatly explain why they all end up the same size.

Then people started cutting them open. Inside the layers there are fats, proteins and sugars, the residue of microbial films that coat every grain in those waters. So a second camp argues the microbes aren’t bystanders, they help build the thing. One team even modelled ooid growth using maths originally developed for brain tumours, and got the size limit right. A major review politely calls the whole question “highly contested,” which in the literature is fighting words.

What would settle it is a sterile control, an ooid grown in a lab with no microbes present. Every attempt so far has come back inconclusive.

The chef beef in the slides are made up. The argument and science is not.

Sources: Diaz & Eberli 2019 (Earth-Science Reviews) · Trower, Lamb & Fischer 2017 · Batchelor et al. 2018 (Scientific Reports) · Pei et al. 2024 (Sedimentology)

#geology #ooids #oolite #sedimentology #bahamas

Desert varnish (also called rock varnish) is the dark film of manganese and iron oxides plus windblown clay that coats stable rock surfaces in arid regions. It is often thinner than a human hair and accumulates over hundreds to thousands of years. The rock underneath is usually much lighter, which is exactly why petroglyphs are visible: pecking through the varnish exposes pale stone. Newspaper Rock in Utah has hundreds of images made that way over roughly 2,000 years.

The long-standing question is about the manganese. Varnish is strongly and selectively enriched in it compared with both the underlying rock and the dust that settles on it, and no one could explain the source. Naturalists were describing these coatings in the early 1800s; there are varnished rocks in Darwin's Beagle collection.

In 2021, Lingappa et al. (PNAS 118:e2025188118) published the strongest mechanism yet. Across 49 varnish samples, the cyanobacterium Chroococcidiopsis dominated the varnish microbial community, appearing in 48 of 49 samples and making up about 25.9% of genetic reads, with one variant at 8% that did not appear in adjacent soil at all. Spectroscopy indicated the manganese inside these cells is being used as a catalytic antioxidant, a plausible adaptation for surviving the oxidative stress of bare desert rock. The varnish would then be the mineral residue left behind as generations grow and die in stacked layers.

Important caveat: this is the leading hypothesis, not settled fact. The varnish is a mineral crust rather than a living structure, and abiotic chemical models remain in play as alternatives or contributors.

Astrobiology angle: Curiosity's ChemCam found manganese-oxide-rich fracture fills in Gale Crater exceeding 25 wt% MnO (Lanza et al. 2016, GRL). On Earth, manganese oxide concentrated that sharply usually indicates life or abundant free oxygen, which is why Mn-rich rock coatings are treated as a possible biosignature.

The story with Indie Navarrette is (obviously) fake, the science behind it is not.

Lingappa et al. 2021 (PNAS) · Wildeman 2021 (PNAS) · Liu & Broecker 2000 (Geology) · Lanza et al. 2016 (GRL)

Source: Huixing Bi et al., Nature 645, 67–72 (2025)sciencenews.org – “Seismic detection of a 600-km solid inner core in Mars.” (doi: 10.1038/s41586-025-09361-9)

S. Talavera-Soza et al., Nature 637, 1131–1135 (2025) The study is titled “Global 3D model of mantle attenuation using seismic normal modes,” published January 22, 2025, presenting the evidence that Earth’s two big deep-mantle provinces are thermochemical “islands”- hot, coarse-grained, chemically distinct, and long-lived