u/Geoscopy

The "Earth's core reversed direction" headlines have been doing the rounds again, and most of them oversell what the science actually shows. The inner core isn't reversing direction in any absolute sense, it's still rotating eastward with the rest of the planet. What changed is its rotation relative to the mantle and crust above it. For decades the inner core was running slightly faster than the surface. Around 2010 it slowed, and since then it's been drifting backwards through the same path at roughly 2.5x the slower rate.

The part I find more interesting than the headline is how seismologists figured this out at all. The inner core is 5,150 km down. No instrument has ever reached it. The only way to read what is happening down there is with seismic waves passing through it.

The 2024 Nature study used repeating earthquakes from the South Sandwich Islands, recorded at seismic arrays in Alaska and northern Canada. Earthquakes recurring on the same fault patch produce nearly identical seismograms, unless something has changed along the path between source and receiver. When the team found that waveforms from 2023 were lining up with waveforms from before 2008, that was the signal that the inner core had drifted forward and then drifted back to roughly where it started.

None of this is going to stop the planet or flip the magnetic field. The effect on the length of day is on the order of a millisecond per year, smaller than the effect of melting ice sheets.

I wrote the full piece going from Inge Lehmann's 1936 discovery of the inner core through to the February 2025 follow-up paper, where the same team found that the surface of the inner core itself may be deforming.

https://geoscopy.com/earths-inner-core-reverses-its-spin-learn-why/

Two papers published earlier this year revised the standard Snowball Earth picture in different directions, and I wrote a long-form piece tying them into how we got the Cryogenian glaciation hypothesis in the first place.

The new work:

• Minsky, Wordsworth, Johnston & Knoll (PNAS, April 2026) argue the 56-Myr Sturtian glaciation was not one continuous freeze but a limit cycle, repeated short Snowball and hothouse swings driven by weathering of the Franklin Large Igneous Province. This addresses the duration problem: conventional models say a hard Snowball should self-terminate in ~5–15 Myr, not 56.

• Griffin, Gernon et al. (EPSL, February 2026) measured 2,640 annual varves in the Port Askaig Formation on the Garvellach Islands and pulled out Schwabe (~11 yr) and Gleissberg (~80–90 yr) solar cycles plus interannual ENSO-band periodicities. Their coupled-model runs only reproduce the multidecadal signal if roughly 15% of the ocean stayed ice-free.

The article also covers the four classical lines of evidence (tropical diamictites, low-latitude paleomagnetism, cap carbonates, the return of banded iron formation), the Franklin LIP weathering trigger, Kirschvink's 1992 paragraph, the Hoffman et al. 1998 Science reframing, the deglaciation pCO₂ threshold debate from Caldeira & Kasting through Pierrehumbert to the recent melt-pond physics work, and the refugia question for Cryogenian eukaryotes. The Tasistro-Hart et al. 2025 PNAS paper constraining the Marinoan to ~4 Myr is in there too.

Curious what people here think about the limit-cycle model: does it actually solve the duration problem, or does it push it down to a different question about whether the Franklin basalt inventory really stays weatherable for 56 Myr?

Tanis is a fossil deposit in the Hell Creek Formation, southwestern North Dakota, that preserves the day the asteroid hit, 66 million years ago, 3,050 kilometres from the Chicxulub impact crater in Mexico. The site contains articulated paddlefish and sturgeon with impact-melt spherules wedged between their gill rakers, capped by an iridium- and shocked-quartz-rich clay layer that matches K-Pg boundary sites worldwide.

The deposit also tells us the season the dinosaurs went extinct (boreal spring, confirmed independently by two research teams), what kind of asteroid hit Earth (a carbonaceous chondrite from beyond Jupiter's orbit, based on ruthenium isotope analysis published in Science in 2024), and how a 10-metre surge of water reached an inland river within an hour of impact (seismically induced seiche from the Western Interior Seaway, not a direct tsunami).

The article covers the geology, the dating evidence, the seasonality debate, the impactor provenance, the LeVeque et al. 2024 surge modelling, and the Robert DePalma data-handling controversy and Manchester misconduct investigation. Full references included.

The article looks at why the Siberian Traps were so destructive: not only because of lava, but because magma intruded into coal, evaporites, and organic-rich sediments, releasing carbon, sulphur, halogens, and toxic metals into the atmosphere and oceans.

It covers the Meishan boundary, Siberian sill intrusions, ocean anoxia, acidification, the “Lystrosaurus world” after the collapse, and why recovery took millions of years.

The largest earthquake in North American history happened in 1700. Nobody on the continent wrote it down. The date was pinned to a single winter night, three centuries later, by cross-referencing buried marshes in Washington with Japanese village records of a tsunami that hit Honshu with no felt earthquake.

About 200 km beneath New England, seismic waves slow down inside a roughly 350 to 400 km wide zone of unusually hot mantle known as the Northern Appalachian Anomaly.

A 2025 paper argues that this “heat blob”suggests a migrating mantle instability triggered when Greenland and North America split apart near the Labrador Sea around 80–90 million years ago.

If the model is right, the Appalachians may still be partly supported from below by deep mantle buoyancy.

I wrote a long-form explainer on Tuzo and Jason, the two continent-sized Large Low Shear-Wave Velocity Provinces sitting at the base of Earth’s mantle, one beneath Africa and one beneath the Pacific.

The article covers how seismologists found them through tomography, why their margins are often linked to mantle plumes, how they may relate to hotspots and flood-basalt provinces like Hawaii, Réunion/Deccan, and Siberia, and what the current origin debate looks like.

The most interesting part to me is that we still do not know what they are made of. Some models treat them as ancient piles of subducted oceanic crust. A newer 2025 Nature Geoscience paper argues they may instead be primordial residues formed when material exsolved from Earth’s cooling core into a basal magma ocean. The Theia-impact idea is also still in play.

I tried to keep the article readable while still being careful about the uncertainties, especially around plume reconstructions, LLSVP stability, ULVZs, and the “graveyard of slabs” vs primordial-origin debate.

Would be very interested to hear what people here think, especially from anyone working on mantle geophysics, geochemistry, tomography, or plume modelling.

Natural hydrogen, the kind generated underground by water reacting with iron-rich rocks, has gone from a Malian curiosity to a multi-billion-dollar exploration category in a decade. The geology, the discoveries in Mali, Albania, Kansas and Lorraine, and where the skeptics are right.

5.3 million years ago, the Mediterranean nearly stopped being a sea.

Cut off from the Atlantic, it became a vast evaporating basin of salt. Then the ocean broke back in.

The story of the Messinian Salinity Crisis and the Zanclean megaflood:

https://geoscopy.com/when-the-mediterranean-vanished-the-600000-year-drought-and-the-megaflood-that-ended-it/

At Pozzuoli, near Naples, three Roman marble columns carry a strange dark band: holes bored by marine molluscs.

They are a biological watermark from the centuries when the ground sank below the Mediterranean, and later rose again.

That slow rise and fall is called bradyseism. At Campi Flegrei, it is the visible pulse of a restless volcanic caldera beneath one of Europe’s densest coastal regions. INGV says the current bradyseismic phase began in 2005 and had produced about 144 cm of uplift by April 2025.

The full story, from a Roman market to modern earthquake swarms, is now on geoscopy.com.

Image source: “Macellum - 161010.jpg,” described on Wikimedia Commons as the ruins of the Macellum in October 2017. Photo by Rolf Cosar / Wikimedia Commons, CC BY-SA 4.0.

#Geoscopy #CampiFlegrei #Volcanoes #Geology #EarthScience