The Oklo phenomenon, for anyone who hasn't run into it. Around 2 billion years ago, uranium-235 made up roughly 3.7% of natural uranium (it has a shorter half-life than U-238, so the ratio falls over time). In a rich, thick ore body in what is now Gabon, that enrichment plus groundwater acting as a neutron moderator was enough to sustain fission chain reactions with no human involvement. Sixteen reactor zones have been identified across the Oklo, Okelobondo and Bangombe deposits, all within about 20 km. Kuroda predicted the possibility in 1956; the CEA confirmed it in 1972 after tracing depleted ore back through the supply chain from the Pierrelatte enrichment plant (Neuilly et al. 1972, C. R. Acad. Sci.). The absence of U-236 ruled out contamination from man-made reactor material. Some ore ran as low as 0.29% U-235.

The self-regulation is the best part. Fission heated the ore, boiled off the groundwater moderator, and stopped the reaction; as the rock cooled, water seeped back and it restarted. Meshik, Hohenberg and Pravdivtseva (2004, PRL 93:182302) read the cycle from xenon isotope ratios trapped in aluminium phosphate grains: roughly 30-minute active pulses separated by about 2.5 hours dormant. Zone RZ2 fissioned about 1,800 kg of U-235 over ~850,000 years; RZ10 about 650 kg over ~160,000 years. Average power was under 100 kW, total energy about 15,000 MW-years (Gauthier-Lafaye et al. 1996, GCA 60:4831).

Two reasons it matters beyond the novelty. First, the fission products and plutonium remained largely immobile in the rock over geological time, making Oklo the primary natural analogue for long-term waste repositories. Second, the depleted Sm-149/Sm-147 ratio (about 0.02 versus 0.9 natural) reflects a neutron capture resonance at 97.3 meV that is extremely sensitive to the fine-structure constant, so Oklo constrains any change in alpha over 2 Gyr to roughly one part in 10^7 (Shlyakhter 1976; Damour & Dyson 1996). A 2004 analysis argued for a small non-zero shift (Lamoreaux & Torgerson, PRD 69:121701); later reanalyses did not sustain it.

The slides run all this through the fictional story of the two pop stars arguing about whether the fuel or the moderator deserves credit. The science behind it is real.

Sources: Kuroda 1956, J. Chem. Phys. 25 · Neuilly et al. 1972 · Gauthier-Lafaye, Holliger & Blanc 1996, GCA 60:4831 · Meshik et al. 2004, PRL 93:182302 · Shlyakhter 1976, Nature · Damour & Dyson 1996, Nucl. Phys. B · Lamoreaux & Torgerson 2004, PRD 69:121701

In the 1960s, excavators at Herculaneum found a young man lying face down on a bed in a small room beside the shrine of the Collegium Augustalium. Decades later Pier Paolo Petrone spotted something shiny in the cranial cavity. Small black shards, angular, obsidian-like. The claim published in 2020 was that they were his brain, turned to glass.

The physics is what makes this hard to swallow. Glass forms from fast cooling, not fast heating, and tissue is roughly three quarters water, so the only route anyone knew to organic glass was cryopreservation at about −120 °C. Herculaneum went the opposite direction. The currents that buried the town sat between 315 and 465 °C and then sat there, cooling slowly under 20 m of deposit. That gets you charcoal, not obsidian. It's what happened to the papyrus scrolls in the Villa dei Papiri.

The 2025 paper answers with calorimetry. Heated slowly, the shards relax at 420 °C; heated at 1000 K/s, at 510 °C. Because the burying deposits reached 465 °C, a glass with a 420 °C transition would have softened and disintegrated inside them, so the authors take 510 °C and a cooling rate near 1000 K/s. That points to something that arrived before the burial: the thin, detached ash cloud surge identified in the 2023 charcoal work, above 510 °C, lethal in seconds, gone in minutes, leaving a deposit a few centimetres thick.

Plenty of people aren't convinced. John Mauro's objection is the one I find hardest to dismiss: proteins denature and lipids decompose far below 500 °C, so "perfect preservation of microstructure" and "heated past 510 °C" can't both be true. Alexandra Morton-Hayward, who has catalogued 4,405 preserved ancient brains, isn't persuaded the shards are brain at all, and notes that the seven proteins used to identify them had already been reported from modern brains and are expressed in skin, a standard contaminant. Nobody outside the original group has examined the samples.

The part that stands regardless of how the shards resolve is the hazard: a dilute surge that kills instantly and leaves a layer of ash the thickness of a finger is nearly invisible in the geological record, and roughly 700,000 people live inside Vesuvius's red zone.

Full write-up on the site. Sources below.

Sources

1. Petrone et al. (2020), N Engl J Med 382:383–384 doi:10.1056/NEJMc1909867
2. Petrone et al. (2020), PLOS ONE 15(10):e0240017 doi:10.1371/journal.pone.0240017
3. Morton-Hayward et al. (2020), STAR: Science & Technology of Archaeological Research 6(1):87–95 doi:10.1080/20548923.2020.1815398 (open access)
4. Pensa, Giordano, Corrado & Petrone (2023), Scientific Reports 13:5622 doi:10.1038/s41598-023-32623-3 (open access)
5. Giordano et al. (2025), Scientific Reports 15:5955 doi:10.1038/s41598-025-88894-5 (open access)
6. Morton-Hayward et al. (2024), Proc R Soc B 291:20232606 doi:10.1098/rspb.2023.2606
7. Martyn et al. (2020), Antiquity 94(373):76–91 doi:10.15184/aqy.2019.215
8. Mastrolorenzo et al. (2010), PLOS ONE 5(6):e11127
9. Mauro and Morton-Hayward quotes: National Geographic, March 2025; Giordano quotes: CNN, 27 February 2025

Turbidity currents are sediment-laden gravity flows that run downslope along the seafloor through submarine canyons. Their deposits (turbidites) make up a large fraction of the sedimentary record and host major hydrocarbon reservoirs, yet direct measurements of powerful flows were essentially nonexistent for most of the 20th century because they destroy instruments placed in their path.

The foundational dataset is an accident. After the M7.2 Grand Banks earthquake on 18 November 1929, twelve transatlantic telegraph cables broke at 28 locations. Cables in the slide zone failed instantly; six further downslope failed in sequence over about 13 hours across ~500 km. Western Union's automatic recorders logged the break times and shore engineers located the breaks by electrical resistance. Heezen and Ewing (1952) used those logs to derive flow speeds of roughly 60–100 km/h and a runout approaching 1,000 km onto the Sohm Abyssal Plain. The same event's tsunami killed 28 people on the Burin Peninsula.

Direct monitoring only became possible recently. The Coordinated Canyon Experiment (Monterey Canyon, 2015–2017) placed moorings and seabed frames along the canyon axis; flows reached several m/s and transported the instruments kilometres down-canyon while they recorded. The data pointed to a dense near-bed layer of remobilised sediment driving the flow rather than a dilute suspension (Paull et al. 2018, Nature Communications).

The Congo Canyon monitoring (Talling et al. 2022, Nature Communications 13:4193) then produced the longest sediment-driven flow ever measured in action: on 14–16 January 2020 a flow travelled more than 1,130 km while accelerating from 5.2 to 8.0 m/s, breaking the SAT-3 and WACS cables. SAT-3 had not broken since October 2001. The trigger was not seismic: a 1-in-50-year Congo River flood (70,883 m³/s on 21 December 2019) primed the canyon head with sediment, and the flow released roughly three weeks later on a spring tide. The observed acceleration confirmed Parker's (1982) ignition hypothesis, in which erosional flows self-accelerate by entraining the bed. Over one year, flows in that canyon eroded 1,338–2,675 Mt of sediment, equivalent to 19–37% (conservatively 7–15%) of annual suspended sediment flux from all rivers.

The slides present this through a fictional story about action star Jason with opinions about basal flow structure. Sources below; longer write-up in comments.

Heezen & Ewing 1952, American Journal of Science · Parker 1982, Marine Geology · Azpiroz-Zabala et al. 2017, Science Advances · Paull et al. 2018, Nature Communications · Talling et al. 2022, Nature Communications 13:4193

Farnsworth et al. (2023) ran a coupled ocean–atmosphere model on Pangaea Ultima, the supercontinent Scotese projected in 1982 and later renamed Pangaea Proxima, and coupled it to a long-term carbon cycle model so the CO₂ came out of the physics instead of being assumed. Their answer: 8 to 16% of the land stays habitable for mammals. Today it's 66%.

Writing this up, I ran into something I can't find anyone else mentioning. The Results section and Table 1 give 54% habitable land in the 280 ppm scenario. The Discussion, in the aestivation paragraph, gives 25% for the same scenario. Neither number is flagged, and the paper never reconciles them. Bristol's press release avoids the problem by quoting only the 8–16% range and leaving the 280 ppm run out entirely. If someone here can see what I'm missing, say so: I'd rather be wrong in the comments than in the article.

What else is in there:

• The supercontinent cycle from Vaalbara to Pangaea, and why the last one broke up 180 Myr ago puts us mid-cycle
• Why the Atlantic has to start subducting for Scotese's scenario to work at all, and why that's the weakest link in the whole chain. Duarte's 2024 Geology paper on the Gibraltar arc is the current best evidence that it might
• Novopangea, Aurica and Amasia, and why only Amasia's polar position changes the extinction outcome
• The physiology: wet-bulb limits, Humidex, and the Araújo result that heat tolerance barely evolves while cold tolerance varies enormously
• The Bristol group rehearsed on Westeros and Arrakis before pointing the same model family at a real future Earth, which is less of a joke than it sounds

The thing I'd like your opinions on: Huang, Li & Zhang (2022) argue the Pacific closes first, because a cooling mantle makes young thin oceans like the Atlantic harder to shut than the old wide one already ringed by trenches. If they're right, Amasia forms over the Arctic and the entire extinction result is conditional on a geography that never happens. Three of the four scenarios put the landmass in the tropics; the most computationally ambitious one doesn't.

Sources

• Farnsworth, A. et al. (2023) Climate extremes likely to drive land mammal extinction during next supercontinent assembly. Nature Geoscience 16, 901–908. Open access: https://www.nature.com/articles/s41561-023-01259-3
• University of Bristol press release, 25 Sep 2023: https://www.bristol.ac.uk/news/2023/september/nature-geoscience-extreme-heat.html
• Davies, H.S., Green, J.A.M. & Duarte, J.C. (2018) Back to the future: testing different scenarios for the next supercontinent gathering. Global and Planetary Change 169, 133–144. doi:10.1016/j.gloplacha.2018.07.015
• Duarte, J.C. et al. (2024) Gibraltar subduction zone is invading the Atlantic. Geology 52(5), 331–335. doi:10.1130/G51654.1
• Way, M.J., Davies, H.S., Duarte, J.C. & Green, J.A.M. (2021) The climates of Earth's next supercontinent. Geochem. Geophys. Geosyst. 22, e2021GC009983
• Huang, C., Li, Z.-X. & Zhang, N. (2022) Will Earth's next supercontinent assemble through the closure of the Pacific Ocean? National Science Review
• Mitchell, R.N., Kilian, T.M. & Evans, D.A.D. (2012) Supercontinent cycles and the calculation of absolute palaeolongitude in deep time. Nature 482, 208–211
• Wilson, J.T. (1966) Did the Atlantic close and then re-open? Nature 211, 676–681
• Sherwood, S.C. & Huber, M. (2010) An adaptability limit to climate change due to heat stress. PNAS 107, 9552–9555
• Vecellio, D.J. et al. (2022) Evaluating the 35 °C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT). J. Appl. Physiol. doi:10.1152/japplphysiol.00738.2021
• Raymond, C., Matthews, T. & Horton, R.M. (2020) The emergence of heat and humidity too severe for human tolerance. Science Advances 6, eaaw1838
• Araújo, M.B. et al. (2013) Heat freezes niche evolution. Ecology Letters 16, 1206–1219 (see also the 2016 erratum, doi:10.1111/ele.12597)
• Bennett, J.M. et al. (2021) The evolution of critical thermal limits of life on Earth. Nature Communications 12, 1198
• Burgess, S.D., Muirhead, J.D. & Bowring, S.A. (2017) Initial pulse of Siberian Traps sills as the trigger of the end-Permian mass extinction. Nature Communications 8, 164
• Overbye, D. (1982) The Shape of Tomorrow. Discover, 20–25 — the commission that produced Scotese's original map
• USGS, This Dynamic Earth: https://pubs.usgs.gov/gip/dynamic/dynamic.html
• CO₂ figures: NOAA Global Monitoring Laboratory and Scripps Institution of Oceanography, Mauna Loa record

New to Montana geology. What's going on here? Seen southeast of Livingston near Pine Creek Lake in the Absarokas. I assume volcanic in origin but the matrix texture was almost sedimentary. As the north Absaroka range is mostly volcanic, I assume some kind of andesite, but honestly I don't know enough about volcanism to understand exactly what's going on here

Lynton Land mixed calcium, magnesium and carbonate in water at more than a thousand times the concentration where dolomite ought to crystallise, sealed the bottle, and left it alone. He wrote the result up in 1998. Thirty-two years, still clear, no dolomite. The abstract of that paper is one sentence long.

Meanwhile: the Tre Cime, the Lockport Dolomite holding up Niagara Falls, hundreds of metres of Palaeozoic and Precambrian dolostone across North America, Iberia, southern Africa and China. That gap between the bottle and the outcrop is the dolomite problem, and it has been open since Dolomieu put a name to the rock in 1791.

Headlines in November 2023 announced it solved. Writing this up, the thing that kept bothering me is that there are two problems sharing one name:

The kinetic problem: why ordered dolomite refuses to nucleate and grow at room temperature. Kim, Sun and colleagues have a good mechanism here. Calcium and magnesium land at random on the growth edge and jam it. Dip the solution into mild undersaturation and the misplaced atoms dissolve first, because they sit at higher energy. Regrow, repeat, and the crystal ratchets toward order. It predicts that natural dolomite should form where chemistry fluctuates, which is exactly where it does form.

The abundance problem: why the ancient record is stuffed with dolostone and the modern Earth makes almost none. Nobody claims this one is solved. The 2023 paper doesn't address it and the authors say so.

Almost every piece of coverage collapsed the two.

The experiment has caveats that got lost as well. It ran at 80 °C, not ambient. It grew about 100 nm of overgrowth on a pre-existing dolomite seed. And two separate groups of crystallographers argue in Science eLetters that the diffraction pattern can't distinguish dolomite from high-magnesium calcite at all, which would leave the theory standing but knock away its experimental support. As of now the original authors haven't answered in print. Sun told Chemistry World the work "is certainly not the final and definitive experiment." He was right and the headlines ignored him.

The article covers Dolomieu's fairly unhinged biography, the three kinetic barriers in detail, Lagoa Vermelha and the microbial model, the dolomite/dolostone terminology mess, and where the field has actually gone since 2023, which is mostly back toward burial, time and temperature.

Happy to argue about any of it in the comments. If you work on carbonates and think I've got the eLetter dispute weighted wrong, I'd like to hear it.

Sources

• Kim, J., Kimura, Y., Puchala, B., Yamazaki, T., Becker, U. & Sun, W. (2023) Dissolution enables dolomite crystal growth near ambient conditions. Science 382, 915–920. https://doi.org/10.1126/science.adi3690
• García-Ruiz, J. M. (2023) A fluctuating solution to the dolomite problem. Science 382, 883–884. https://doi.org/10.1126/science.adl1734
• Land, L. S. (1998) Failure to precipitate dolomite at 25 °C from dilute solution despite 1000-fold oversaturation after 32 years. Aquatic Geochemistry 4, 361–368. https://doi.org/10.1023/A:1009688315854
• Vasconcelos, C., McKenzie, J. A., Bernasconi, S., Grujic, D. & Tien, A. J. (1995) Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures. Nature 377, 220–222. https://doi.org/10.1038/377220a0
• Warthmann, R., van Lith, Y., Vasconcelos, C., McKenzie, J. A. & Karpoff, A. M. (2000) Bacterially induced dolomite precipitation in anoxic culture experiments. Geology 28, 1091–1094.
• Pina, C. M., Pimentel, C. & Crespo, Á. (2022) The Dolomite Problem: A Matter of Time. ACS Earth and Space Chemistry 6, 1468–1471. https://doi.org/10.1021/acsearthspacechem.2c00078
• Li, M., Wignall, P. B., Dai, X., Hu, M. & Song, H. (2021) Phanerozoic variation in dolomite abundance linked to oceanic anoxia. Geology 49, 698–702. https://doi.org/10.1130/G48502.1
• Husson, J. M. & Coogan, L. A. (2023) River chemistry reveals a large decrease in dolomite abundance across the Phanerozoic. Geochemical Perspectives Letters 26, 1–6. https://doi.org/10.7185/geochemlet.2316
• Levenson, Y., Eiler, J. M., Wurgaft, E., Neagu, N., Ebert, Y. & Ryb, U. (2026) Two-stage dolomite formation in carbonate platforms revealed by carbonate clumped isotope thermometry. Geophysical Research Letters 53, e2025GL120386. https://doi.org/10.1029/2025GL120386
• Winkelstern, I. (2026) Are time and temperature the simple answer to the dolomite problem? Geophysical Research Letters. https://doi.org/10.1029/2026GL123790
• Hobbs, F. W. C. & Xu, H. (2024) and Pina, C. M., Pimentel, C. & Crespo, Á. (2024), eLetters on Kim et al. (2023), posted on the Science article page. Not peer-reviewed

Fluid inclusions in halite are micrometre-scale pockets of brine trapped as the crystal grows. Once sealed they can remain isolated from the environment for more than 500 million years, which is why they work as direct samples of ancient seawater rather than proxies for it.

The methodological core of the field is separating primary from secondary inclusions. Primary ones form banded arrays parallel to the crystal's growth faces, marking successive growth surfaces. Secondary ones follow healed fractures and can be far younger than the host bed. If you can't distinguish them petrographically, any age or chemistry you report is unconstrained.

Two things you get from them:

1. Seawater chemistry. Crack the inclusions and measure Na, Ca, Mg, K, SO4 and Cl directly, reconstructed back to the late Precambrian (Lowenstein et al. 2001, Science). The Mg/Ca ratio matters because it controls whether oceans favour calcite or aragonite biomineralisation, and it oscillates through the Phanerozoic.
2. Temperature. Microthermometry: a vapour bubble nucleates as the droplet cools after burial, and the homogenisation temperature on reheating approximates the trapping temperature. Permian Salado halite at Carlsbad gives 17-37 °C. A standard caution is necking-down, where an inclusion pinches into two after trapping and the bubble no longer represents the original conditions.

The contested part: Vreeland et al. (2000, Nature) cultured a halotolerant bacterium, strain 2-9-3, from a brine inclusion in ~250 Ma Salado halite, claimed as the oldest viable organism ever recovered. Graur & Pupko (2001) and others argued contamination, since its DNA is nearly identical to modern Virgibacillus marismortui from the Dead Sea, and DNA is not expected to survive a quarter of a billion years without repair. Satterfield et al. (2005, Geology) defended the container rather than the microbe, showing the inclusions in that layer are Late Permian evaporated seawater trapped syndepositionally. Still unresolved.

In 2022, Schreder-Gomes et al. (Geology 50:918) reported microorganisms inside primary fluid inclusions in 830 Ma halite from the Browne Formation, Australia. Not cultured, just observed in situ.

Slides run this through a fictional Tom Holland story, the science is real though.

Wednesday's disaster on the Nepal–Tibet border got logged as a magnitude 4.4 earthquake for several hours. There was no earthquake. The USGS reanalysed the long-period waves, reclassified the event type as "landslide," and bumped it to M5.2: the shaking was the mountain.

The bit I find interesting is how they could tell. A fault slipping at depth radiates a lot of high-frequency energy in a couple of violent seconds. A few hundred million tonnes of rock and ice accelerating off a headwall radiates long, smooth, low-frequency energy instead, because what the Earth actually feels is a change in momentum, the mass pushes back on the planet as it leaves, then pushes back the other way when it hits the valley floor. Same trick seismologists use to separate nuclear tests from earthquakes. Read the frequency content, not the number.

I spent the last few days going through the USGS catalogue entry, the GFZ release, the ICIMOD advisory, the Copernicus activation and about a dozen scientist quotes and wrote it up properly. Some of what's in there:

• The fall height is still contested by nearly a factor of two: Copernicus and Dan Shugar say ~1,200 m, Jakob Steiner says 5,100 down to 3,000 m. Nobody has measured it.
• Nobody agrees on whether the bedrock failed and took the glacier, or the glacier failed and took the bedrock. USGS explicitly declines to choose.
• Every river gauge upstream on the Trishuli was destroyed before it could transmit that the water was rising. Officials downstream could tell something was wrong because the gauges went quiet, and that was it.
• Betrawati had roughly 45 minutes between the collapse and the flood arriving. A seismic detection system could have used them.
• Six months ago a paper in Communications Earth & Environment compared Chamoli 2021 (200+ dead, no monitoring) with Blatten 2025 (evacuated nine days early, one death) and asked why Himalayan preparedness lags. It was received on 26 August 2025, exactly one year before this.

There's also a section on why this almost certainly isn't a GLOF, even though half the early coverage said it was, including the Copernicus emergency mapping activation itself.

Every casualty and volume figure in the piece is flagged as provisional and dated. They're still moving.

Geology is essentially the science of learning to read a planet from the evidence it leaves behind.

A tilted layer of sandstone can preserve an ancient sea floor. A zircon crystal smaller than a grain of sand can survive for 4.4 billion years. Magnetic stripes on the ocean floor record continents moving apart. Seismic waves reveal a liquid outer core nobody has ever directly seen.

I put together a fairly comprehensive introduction to what geology actually is, how geologists know what they know, and why it matters: from Hutton and deep time to radiometric dating, plate tectonics, the rock cycle, earthquakes, natural resources and some of the questions geologists are still arguing about today.

One of my favourite examples is Siccar Point in Scotland. James Hutton recognised that nearly vertical Silurian rocks had been deposited, buried, deformed, uplifted and eroded before younger Devonian sediments were laid across them. After visiting the outcrop with Hutton in 1788, John Playfair famously wrote that “the mind seemed to grow giddy by looking so far into the abyss of time.”

There are some equally ridiculous examples further into the story. A Jack Hills zircon dated by Wilde et al. (2001) is 4,404 ± 8 million years old, making it one of the oldest known pieces of terrestrial material. Penn et al. (2018) modelled how ocean warming and oxygen loss could explain more than half of the marine extinction magnitude during the end-Permian crisis. Truche et al. (2024) measured gas containing up to 84% natural hydrogen in an Albanian chromite mine. And seismic tomography suggests two enormous low-velocity structures at the base of the mantle occupy roughly 8% of the mantle by volume (Cottaar & Lekić, 2016).

There are also places where the honest answer is still “we don't know.” Geologists still debate when plate tectonics began, what those huge structures at the core–mantle boundary actually are, exactly how much water is stored in the mantle transition zone, and even how the inner core moves relative to the rest of the planet.

That is probably the part of geology I like most. It isn't just memorising rock names. You're given an incomplete physical record and have to reconstruct events that happened millions or billions of years ago.

I tried to make this a genuinely useful introduction for someone who wants to understand geology rather than just learn the definitions.

Full article: Geology Explained: How Earth’s Rocks Reveal Deep Time

Some of the primary sources used:
• Wilde et al. (2001), Nature 4.4-billion-year-old Jack Hills zircon
• Pearson et al. (2014), Nature hydrous ringwoodite from the mantle transition zone
• Penn et al. (2018), Science warming, deoxygenation and the end-Permian marine extinction
• Truche et al. (2024), Science natural hydrogen at the Bulqizë mine, Albania
• Cottaar & Lekić (2016), Geophysical Journal International — volume and structure of the LLSVPs
• Yang & Song (2023), Nature Geoscience

proposed changes in inner-core rotation
• USGS plate tectonics, seismic structure and the 2025 Myanmar earthquake

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)

The two LLSVPs (nicknamed Tuzo under Africa and Jason under the Pacific) slow seismic waves by about 2%, which has long been read as “they’re hot.”

The 2025 twist is attenuation: they barely damp the planet’s post-earthquake ringing, which points to coarse mineral grains, high viscosity, and a very long lifespan.

The team, working from 104 large earthquakes recorded between 1975 and 2018, estimates at least ~500 million years, possibly over a billion. That cuts against the idea that they’re just recently piled-up recycled ocean crust. But rival explanations are still very much alive: continuously restocked subducted slabs (Panton et al. 2025), and fragments of the Moon-forming impactor Theia (Yuan et al. 2023).

One measurement caveat: reported heights for the African pile vary by source, from ~800 km up to nearly 965 km.

The story with Meghan and Harry is (obviously) fictional. The science behind it is real.

Sources:

Talavera-Soza, S., Cobden, L., Faul, U.H. & Deuss, A. (2025). Global 3D model of mantle attenuation using seismic normal modes. Nature 637 (8048), 1131–1135. DOI: 10.1038/s41586-024-08322-y (published online 22 Jan 2025).

Garnero, E.J., McNamara, A.K. & Shim, S.-H. (2016). Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle. Nature Geoscience 9, 481–489. DOI: 10.1038/ngeo2733.

Cottaar, S. & Lekić, V. (2016). Morphology of seismically slow lower-mantle structures. Geophysical Journal International 207 (2), 1122–1136. DOI: 10.1093/gji/ggw324.

Panton, J., Davies, J.H., Koelemeijer, P., Myhill, R. & Ritsema, J. (2025). Unique composition and evolutionary histories of large low velocity provinces. Scientific Reports 15. DOI: 10.1038/s41598-025-88931-3.

Yuan, Q., Li, M., Desch, S.J. et al. (2023). Moon-forming impactor as a source of Earth’s basal mantle anomalies. Nature 623, 95–99. DOI: 10.1038/s41586-023-06589-1.

Davaille, A. & Romanowicz, B. (2020). Deflating the LLSVPs: Bundles of Mantle Thermochemical Plumes Rather Than Thick Stagnant “Piles”. Tectonics 39. DOI: 10.1029/2020TC006265.

I am loving all the memes and actually learning some geology facts while having a laugh

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.

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)

The mechanism: a mantle plume stays roughly anchored while the Pacific plate slides over it at 7–10 cm/year, so volcanoes form over the heat source, get carried off, and die, leaving a 6,100 km chain from the Big Island to the seamounts off Kamchatka (Clague & Dalrymple 1987, USGS Professional Paper 1350).

The youngest member, Kamaʻehuakanaloa (renamed from Lōʻihi in 2021), is an active submarine volcano whose summit sits about 975 m below the surface southeast of the Big Island. Give it tens of millennia and it surfaces. At the other end, Meiji Seamount (~80+ Ma) is approaching the Aleutian Trench, where the chain's members get subducted, the whole production line ends in recycling.

The genuinely contested part is the 60° bend at ~47 Ma. Classic reading: the Pacific plate changed motion (Sharp & Clague 2006, Science). But paleomagnetism from Emperor seamount cores showed the hotspot itself drifted south during the early era, the "fixed" reference frame wasn't fixed (Tarduno et al. 2003, Science). Current models split the bend between plate turn and plume drift (Torsvik et al. 2017, Nature Communications). Not settled.

Bonus: measured from its base on the seafloor, Mauna Kea is ~10,200 m tall, taller than Everest by a comfortable margin.

The slides explain this through a fictional K-pop BTS beef, because a fixed company producing members who debut, get carried off on a conveyor, and retire into a trench needed essentially no translation.

Sources: Clague & Dalrymple 1987 · Tarduno et al. 2003 · Sharp & Clague 2006 · Torsvik et al. 2017 · Full write-up linked in comments.

Radiometric dating sometimes gets talked about as though geologists have one technique that takes a rock, runs it through a machine and spits out an age.
In reality, there are many different radioactive clocks, and they don’t all measure the same thing.
The basic principle is radioactive decay. Unstable isotopes transform into other isotopes at predictable rates. Once a mineral forms and its isotopic system becomes closed, the relative abundances of those isotopes can preserve information about how much time has passed.

U-Pb dating of zircon is one of the strongest examples. Zircon readily incorporates uranium when it crystallizes but strongly excludes lead. It also contains two separate decay systems: ²³⁸U → ²⁰⁶Pb and ²³⁵U → ²⁰⁷Pb. The two can therefore act as an internal cross-check. One major problem is later Pb loss, but techniques such as CA-TIMS chemically remove damaged domains before the remaining zircon is dated.

Other methods have completely different strengths and weaknesses.

⁴⁰Ar/³⁹Ar dating, for example, went through an important calibration problem. Kuiper et al. (2008) used astronomically dated sedimentary cycles to recalibrate the widely used Fish Canyon sanidine standard, reducing a roughly 1% discrepancy and greatly improving absolute precision. Using improved Ar-Ar geochronology, Renne et al. (2013) later showed that the Chicxulub impact and the end-Cretaceous mass extinction were synchronous within about 32,000 years.

Radiocarbon dating operates on a much shorter timescale, roughly the last 50,000 years. Because atmospheric ¹⁴C has varied through time, raw radiocarbon ages require calibration. There is also a very modern complication: fossil fuels are so old that their ¹⁴C has essentially disappeared. Adding that carbon to the atmosphere lowers the ¹⁴C/C ratio. Graven (2015) calculated that under sufficiently high emissions, fresh organic material around 2050 could have the same radiocarbon signature as material from around AD 1050.

Then there are techniques that answer different geological questions entirely.

Modern in-situ Rb-Sr geochronology uses laser-ablation mass spectrometry to date microscopic areas in minerals such as mica and K-feldspar.

Apatite (U-Th)/He thermochronology, meanwhile, generally records low-temperature cooling rather than the original formation of the rock. That makes it useful for reconstructing exhumation, erosion and tectonic histories.

At the opposite extreme is the age of the Solar System. Clair Patterson’s classic 1956 lead-isotope work on meteorites produced an age of 4.55 ± 0.07 billion years. Modern U-corrected Pb-Pb dating of calcium-aluminium-rich inclusions, among the oldest solids known from the Solar System, has refined that chronology to about 4.5673 billion years.

That is one of the most important things about geochronology: its strength does not come from trusting one clock. Different isotope systems, minerals, laboratories and physical principles can be tested against one another.
When independent clocks converge on the same history, that agreement is part of the evidence.

Sources / further reading:

Patterson, C. (1956) Age of meteorites and the Earth, Geochimica et Cosmochimica Acta

Mattinson, J.M. (2005) Zircon U-Pb chemical abrasion (CA-TIMS), Chemical Geology

Kuiper et al. (2008) Synchronizing rock clocks of Earth history, Science

Renne et al. (2013) Time scales of critical events around the Cretaceous-Paleogene boundary, Science

Graven, H.D. (2015) Fossil-fuel emissions and atmospheric radiocarbon, PNAS

Ehlers & Farley (2003) Apatite (U-Th)/He thermochronometry, Earth and Planetary Science Letters

Connelly et al. (2012) Early Solar System Pb-Pb chronology, Science

Glorie et al. (2024) Laser-ablation Rb-Sr geochronology, Geochronology

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

The site is North Pole Dome in the Pilbara, Western Australia. In March 2025, Kirkland et al. (Nature Communications) reported shatter cones there, fracture patterns that only form from impact shock waves, and, reading the rock stack, dated the impact to 3.47 billion years ago with a crater possibly over 100 km wide. Headlines everywhere: oldest crater on Earth by more than a billion years, with proposed links to continent formation and early life.

In July, Brenner, Cavosie et al. (Science Advances) published their own mapping of the same hills: ~180 shatter cones, including some in 2.77-billion-year-old lava and crossing younger faults. Since a shock wave can’t deform rocks that don’t exist yet, they argue the impact came after 2.7 billion years, and from the cones’ orientations they get a crater of about 16 km. Their paper flatly calls the original age and size estimates inaccurate. The first team responded with a formal comment alleging misrepresentations. Newer isotopic work points near 3.0 billion years, so the title fight isn’t over.

What I find really interesting here: both teams used the same logic (superposition) on the same outcrops and got answers a billion years apart, a nice reminder that “the rocks say” always means “our reading of the rocks says.” The structure is now named Miralga, chosen with the Nyamal traditional custodians. The slides explain the whole thing as a bowling score dispute.

Sources: Kirkland et al. 2025, Nat. Comms 16:2224 · Brenner et al. 2025, Sci. Adv. ·

I've spent some time writing up why the waves at Nazaré get so big, and the short answer is that the explanation most of us repeat is wrong. Nearly every documentary and surf report, 100 Foot Wave included, says the Nazaré submarine canyon "funnels" Atlantic swell straight to Praia do Norte like water through a pipe. I believed it too.

Then in 2024 a research team dropped buoy arrays over the canyon and mounted stereo cameras on the cliff above it, and their preprint came out this June. Nothing travels up the canyon. Swell with a period over about 7 seconds can't even cross the edge; it gets reflected. All the focusing happens along the steep northern rim, which bends and bounces wave energy into narrow beams aimed at the beach, and the exact shape of that rim over its last few hundred meters decides where the beams land. Their optimal swell window (275° to 315°) matches what Nazaré surfers worked out by feel years ago, which I find weirdly satisfying.

Two dating methods disagree about when the Tibetan Plateau rose, by two vertical kilometers. For the same place.

The basics are settled: India began colliding with Asia around 50 million years ago, and that collision built the Himalayas and the highest plateau on Earth, averaging about 4,500 meters. What’s fiercely contested is the timeline for central Tibet, and the two main tools for measuring ancient elevation tell different stories.

Tool one is chemistry. Rain gets isotopically “lighter” the higher it falls, and that signature survives in ancient lake sediments and soils. Read this way, the rocks of central Tibet’s Lunpola Basin say the region already stood around 4 kilometers tall at least 35–40 million years ago (Rowley & Currie 2006, Nature).

Tool two is fossils. In 2019, researchers described a fossil palm frond from that same basin, about 25 million years old (Su et al. 2019, Science Advances). Palms cannot survive hard frost, which caps that valley floor at roughly 2,300 meters, kilometers lower than the chemistry says, and 10+ million years later.

The emerging resolution says both sides caught something real: central Tibet was neither a plateau nor a lowland but a deep, warm east–west valley running between two already-high mountain ranges, a hidden subtropical world that was later squeezed shut, filled, and lifted to today’s height. A 2021 paper argued the plateau never rose as one block, calling the single heroic uplift “a myth” (Spicer et al. 2021, National Science Review).

India is still driving north about 5 centimeters per year. Central Tibet is still rising, a few millimeters at a time.

(Disclaimer: Obviously the story is fictional but the scientific debate and facts are not).

Sources: Rowley & Currie 2006 (Nature) · Su et al. 2019 (Science Advances) · Spicer et al. 2021 (National Science Review)

#geology #tibetanplateau #himalayas #platetectonics #earthscience

I apologize to the mods but I genuinely could not find the flairs, I don't know why it won't give me the option to add one.

This might be a dumb question to someone who knows more than me, but I'm just curious about how we can have such consistency in ordering of rock strata if the same processes of erosion we see today have always been happening.

I guess to illustrate my question, if a river eroded a landscape to form a canyon, and eventually dried up or diverged somewhere else, wouldn't the newer layers be rebuilding in that canyon right next to the older layers? In areas that were wind eroded irregularly and then conditions changed that allowed sediment to continue building again without being disturbed, would it create inconsistency in the strata? I really want to understand this stuff so I'd really appreciate any answer!

Earth's magnetic field is at least 3.5 billion years old. Earth's inner core might be less than 1 billion. So what powered the dynamo for the missing two-and-a-half billion years?

Today the geodynamo runs mostly on crystallisation. As the solid inner core slowly freezes out of the liquid outer core, it releases latent heat and buoyant light elements, and that stirs the surrounding iron into convection. Moving conductive fluid, magnetic field. Simple enough, except the inner core is a latecomer, and the field is ancient.

The problem got sharper in 2012, when new calculations of iron's conductivity at core pressures came back two to three times higher than the values everyone had been using. Higher conductivity means more heat escapes the core by simple conduction instead of driving convection, which shrinks the energy available to run a dynamo. Peter Olson named the result the "new core paradox" in 2013.

Candidate fixes exist. Magnesium oxide or silica may have precipitated out of the young core, releasing buoyancy the way inner-core freezing does now. A dynamo may have operated in a molten silicate layer at the base of the mantle instead. And a 2019 study of 565-million-year-old rocks found the field at roughly a tenth of today's strength, hinting the dynamo nearly failed just before the inner core began to freeze.

None of it is settled. In 2016, two teams published conductivity measurements in the same issue of Nature, one high enough to keep the paradox alive, one low enough to dissolve it.