New drill core penetrates the Mohorovičić Discontinuity (the ‘Moho’)

In 1909 Croatian geophysicist Andrija Mohorovičić examined seismograms of a shallow earthquake that shook the area around Zagreb. To his surprise the by-then familiar time sequence of P-waves followed by the slower S-waves appeared twice on seismic records up to 800 km away. The only explanation that he could come up with was that the first arrivals had travelled directly through the crust to the detector whereas the second set must have followed a longer path: it had travelled downwards to be refracted to reach the surface when it met rocks denser than those at the surface. His analysis revealed a sharp boundary between the Earth’s crust and its mantle at a depth of about 54 km below what was then Yugoslavia. Later workers confirmed this discovery and honoured its discoverer by naming it the Mohorovičić Discontinuity. Difficulty with pronouncing his name resulted in a geological nickname: ‘the Moho’. It can be detected everywhere: at 20 to 90 km beneath the continental surface and 5 to 10 km beneath the ocean floor, thus distinguishing between continental and oceanic crust.

In the late 1950s accelerating geological and oceanographic research that would culminate in the theory of plate tectonics turned its focus on drilling down to the Moho in much the same way as a lust for space travel spawned getting to the Moon. The difference was that the proposers of what became known as the Mohole Project were members of what amounted to a geoscientific glee club (The American Miscellaneous Society), which included a member of the well-financed US National Science Foundation’s Earth Science Panel. The idea emerged shortly after the Soviet Union had launched the Sputnik satellite and rumours emerged that it was proposing deep drilling into the continental crust beneath the Kola Peninsula.  The Mohole’s initial target was the 3.9 km deep floor of the Caribbean off Guadalupe in Mexico and required advanced methods of stabilisation for a new oceanographic ship that was to host the drilling rig.

Huge (tens of metres high) pillars or ‘chimneys’ of carbonates formed by the Lost City hydrothermal vent near the mid-Atlantic ridge (Credit: ETH Zurich)

The Mohole was spudded in 1961, but the deepest of five holes reached only 200 m beneath the sea floor. It recovered Miocene sediments and a few metres of basalt. Deep water drilling was somewhat more complicated than expected and about US$ 57 million was spent fruitlessly. The project was disbanded in 1966 with considerable acrimony and schadenfreude. Nonetheless, the Mohole fiasco made technical advances and did demonstrate the feasibility of offshore drilling. The petroleum industry benefitted and so did oceanography with the globe-spanning deep-sea drilling of ocean floor sediments. The sediment cores produced the 200 million-year exquisitely detailed record of climate change and vast amounts of geochemical data from the basaltic oceanic crust. In 2005 JOIDES (the Joint Oceanographic Institutions for Deep Earth Sampling) had another crack at the Moho. That venture centred on the intersection of the Mid-Atlantic Ridge and the Atlantis Fracture Zone close to the ‘Lost City’ hydrothermal vent. The area around the vent is the site of a huge low-angled extensional fault that has partly dragged the basaltic ocean crust off the mantle beneath causing it to bulge. This provided an excellent opportunity to drill through the Moho. All went well, but 54 days of drilling yielded 1.4 km of basalt but nothing resembling mantle rock. So, again, the Moho had thwarted Science (and research economics). But finally it is beginning to reveal it secrets (see: Voosen, P. 2023. Ocean drillers exhume a bounty of mantle rocks. Science, v. 380 (News) p. 876-877; DOI: 10.1126/science.adi9899

The area around the ‘Lost City’ vent was originally chosen for drilling to examine the chemical processes going on there. Hydrogen emitted by serpentinisation of mantle rocks can combine with carbon monoxide in hydrothermal fluids to create a wide variety of organic compounds, which could be the initial building blocks for the origin of life. As part of the International Ocean Drilling Programme JOIDES decided to launch IODP Expedition 399 to re-examine the area around ‘Lost City’ in more detail. The expedition first tried to continue drilling the 2005 hole, but failed yet again. Finally a new drill site aimed at penetrating the extensional detachment. Within a few days the drill bit punched into mantle rocks and over a 6-week period the expedition had recovered a kilometre of core. The technical accounts for each week of drilling give a flavour of what it must be like to be a part of such a ship-borne expedition as well as describing what emerged in the drill core. It seems like a bit of a jumble, dominated by the mineral olivine– the principal characteristic of the ultramafic mantle – almost pure in the rock dunite and mixed with pyroxenes in various kinds of peridotite. There are also coarse-grained rocks that contain plagioclase feldspar, which cut through the ultramafic materials – gabbros, troctolites and norites.  They are relics of intrusive basaltic magmas that did not make it to the seabed. The samples are variably altered by interaction with watery hydrothermal fluids, with lots of serpentine, talc and even asbestos: the drilling presented a health hazard for a few days. The rocks have been metamorphosed under pressure-temperature conditions of greenschist to amphibolite facies and subject to ductile deformation, probably because of the effect of extensional deformation. Whatever, there is plenty of material to be analysed, including for signs of microbial activity. So, the dreams of a 1950s academic drinking fraternity (they were all men!) have finally been realised. But since those pre-plate-tectonic times many geologists have seen and collected much the same, even putting their index fingers on the Moho itself in the time-honoured fashion. Intricate 3-D geology in ophiolite complexes such as that in Oman, provide such opportunities at the much lower cost of air travel, Land Cruiser hire and camping. Indeed what we know of the structure of the oceanic lithosphere – pillow lavas, sheeted dyke complexes, gabbro cumulates and serpentinised ultramafic mantle – has come from such bodies thrust onto continental crust at ancient plate margins. So, why the celebration in this case? They are the first samples of mantle from young oceanic lithosphere; the rocks of ophiolites may not have formed at mid-ocean ridges. These should give clues to the long-term magmatism that has created the vast abyssal basins that the mantle eventually reabsorbs by subduction. Then, of course, there is the link to biogenic processes at constructive margins that underpinned the return to the active hydrothermal venting at ‘Lost City’.

Flash: Huge rockslide imminent in Swiss village of Brienz

The rockslide above Brienz in eastern Switzerland marked by a white surface bare of vegetation. Credit CHRISTOPH NÄNNI, TIEFBAUAMT GR, SWITZERLAND via the BBC

On 9 May 2023 the authorities of the Albula/Alvra municipality in the Swiss canton of Graubünden informed people living in the small village of Brienz that they must evacuate the area by 18 May as the threat of rock falls from the mountain beneath which they live had triggered a red alert. By 13 May all 130 dwellings had been abandoned.

The danger is posed by an estimated 5 million tons of rock associated with a developing landslide that is now estimated to be moving at around 32 m per year. The village itself had long been creeping down slope at a few centimetres each year, but recently its church spire had begun to tilt and buildings became riven by cracks. Seemingly, engineering attempts to mitigate the hazards have been unsuccessful, and large boulders have already tumbled into the vicinity of Brienz.

Being situated beneath a crumbling scree slope devoid of vegetation that had been developing since the last glaciation, the geological risk to the village comes as no surprise to its population and local authority. The local geology has a thick limestone resting on the thinly bedded Flysch – a metamorphosed sequence of fine-grained turbidites – from which groundwater escapes very slowly, thereby becoming lubricated. A curved (listric) failure zone has developed beneath the exposed mountainside, hence the danger. Acceleration on the listric surface began about 20 years ago.

At least the people of Brienz have been moved to safety, unlike 144 school children and adults in the mining village of Aberfan in South Wales. On 21 October 1966 they were crushed to death by coal-mining waste that suddenly flowed from waste tips on the steep valley side above the village. In that case no warning was given by the National Coal Board authorities who allowed  the tipping witout a thought for its geological consequences.

See also: Petley, D. 2023. The very large incipient rockslide at Brienz in Switzerland. The Landslide Blog (10 May 2023)

Origin of the genus Homo: a Paranthropus link?

Reconstruction of a Paranthropus head (Credit: Jerry Humphrey, Pinterest)

Paranthropoids had large, broad teeth and pronounced cheekbones plus a bone crest on the top of their skulls that were the attachments for powerful jaw muscles, much as in modern gorillas. Unlike gorillas they were definitely bipedal and were more similar to australopithecines. They have been called ‘robust’ australopithecines but they were not significantly taller or heavier. The first to be unearthed at Olduvai, Tanzania in 1959 (Paranthropus boisei) was dubbed ‘Nutcracker Man’ by its finder, and many have implied that paranthropoids’ teeth and powerful jaws were signs of a vegetarian diet that needed a lot of chewing. Yet their teeth do not show the microscopic pitting associated with living primates that eat hard plant parts and nuts, or the heavy wear that results from eating grasses. They probably ate soft plants, such as semi-aquatic succulents or tubers, but meat-eating that causes little dental wear cannot be ruled out. Some specimens are associated with long bones of other animals whose ends are worn, suggesting that they may have used them as tools for digging. Plant remains found at paranthropoid sites suggests that they inhabited woodland, together with coexisting australopithecines. They were around in the form of three successive species from 2.9 to 1.2 Ma, outlasting australopithecines. The later paranthropoids coexisted with Homo habilis and H. erectus: they were clearly just as successfully adapted to their surroundings as were early humans.

In early 2023 evidence was published that associated Oldowan stone tools with remains of Paranthropus, together with deliberately defleshed and cut bones (see also): though association is not proof of a direct link. Interestingly, the hand of a P. robustus found in the Swartkrans cave system in South Africa is consistent with a human-like precision grip, i.e. it had an opposable thumb. Swarkrans also yielded the earliest evidence for the deliberate use of fire about 1.5 Ma ago, associated with remains of both P. robustus and H. erectus. All this suggests that a case could be made for paranthropoids’ being human ancestors – supporting evidence has just been published (Braga, J. et al. 2023. Hominin fossils from Kromdraai and Drimolen inform Paranthropus robustus craniofacial ontogeny. Science Advances, v. 9, article eade7165; DOI: 10.1126/sciadv.ade7165).

Fossil-bearing breccias beneath the floor of the Kromdraai cave in the Cradle of Humankind World Heritage Site 45 km NW of Johannesburg, South Africa yielded the first near-complete P. robustus skull in 1938, another being found in cave breccias at the nearby Drimolen quarry. These deposits also contained remains of four infants assigned to the species, whose teeth and cranial parts were at different stages of juvenile development (ontogeny). José Braga of the University of Toulouse, France and co-workers from South Africa and the USA compared this growth sequence with those teased out from immature specimens of Australopithecus africanus and early Homo.Their tentative conclusion is that Paranthropus robustus is more closely related to early humans than to australopithecines of the same stratigraphic age.

Skull of a probable adult female P. robustus (left) with that of H. habilis (centre) and A. africanus (right). Credits: all from Wikipedia pages

So, it now seems possible that paranthropoids are not ‘robust’ australopithecines in an acceptable, taxonomic sense. Their closer resemblance in early development to early humans, together with their association with early stone tools used for defleshing prey animals, together with evidence for possible their use of fire, further strengthens their candidacy for an ancestral link to humans. The best preserved skulls of Homo habilis and a female P. robustus (males of that species show the distinctive saggital crest) do show close similarities, that of a roughly contemporary A. africanus having distinctly wider cheeks than both. All three species were in life probably of much the same weight and stature (30 to 40 kg and 110 to 130 cm) but H. habilis had a significantly larger brain volume (500 to 900 cm3) than the other two (each ~450 cm3). However, this isn’t proof that the genus Homo evolved from a paranthropoid ancestor. That would require genetic evidence, unlikely to be extracted from specimens because DNA seems to degrade more quickly under the conditions of the tropics than at high latitudes. Debate on ultimate human origins will probably be endless. Perhaps it would make more sense simply to accept that early humans weren’t the only ‘smart kids on the palaeoanthropological block’, one of which left no issue after 1.2 Ma ago.

See also: Handwerk, B. 2023. Who made the first stone tool kits? Smithsonian Magazine, 8 February 2023, article 180981606

Music based on earthquake waves

Many readers will have heard the vibration signal of an earthquake, as recorded by a seismometer, and replayed through a speaker: listen to some examples here. They are eerily like the sounds of falling, multi-storey buildings. Scary, especially if you think of the horrors of the devastation in SE Turkiye and NE Syria caused by the 6 February 2023 magnitude 7.8 event on the East Anatolian Fault system

Since P-waves are very like sound waves, audibly converting the one to the other is relatively simple. However, earthquakes are rarely single events, each major one being preceded by foreshocks and followed by aftershocks, both recurring over weeks or months. Highly active areas are characterised by earthquake swarms that can go on continuously, as happens with sea-floor spreading at mid-ocean ridges. In the case of Yellowstone National Park there are continual quakes, but there the seismicity results from magma rising and falling above a superplume. Most of such swarm-quakes are diminutive, so playing the speeded-up signal through a loudspeaker just sounds like a low, tremulous hiss.

Domenico Vicinanza a physicist at the Anglia Ruskin University in Cambridge UK specialises in creating music from complex scientific data, including those from CERN’s Large Hadron Collider in Geneva, to help interpret them. He has recently turned his hand to the Yellowstone earthquake swarm, converting the amplitudes and frequencies of its real-time seismograph to notes in a musical score: listen to the results here. They are surprisingly soothing, perhaps in the manner of the song of the humpback whale used by some to help with their chronic insomnia.

See also:  Davis, N. Rock concert: Yellowstone seismic activity to be performed on live flute, The Guardian; 8 May 2023

Extraction of ancient human DNA from artefacts

The Denisova cave in southern Siberia is now famous for the evidence that it has provided for Neanderthals and Denisovans and their interbreeding based on DNA recovered from their bones, even a tiny finger bone of the latter. Indeed we would not know of the former existence of Denisovans without such a clue. Scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, responsible for both breakthroughs, also pioneered the extraction of hominin DNA from soil in the cave. Now they have refined the intricate extraction of genetic material to such an extent that detailed hominin DNA sequences can be analysed from ornaments worn by ancient people, in much the same manner as applied in forensic studies of crime scenes (Essel, E. and 22 others 2023. Ancient human DNA recovered from a Palaeolithic pendant. Nature, early release 3 May 2023; DOI: 10.1038/s41586-023-06035-2).

Elk-tooth pendant found at Denisova cave, before cleaning and DNA extraction (top) and after the ‘washing’ procedure (bottom). Credit: Essel et al., Fig 1.

Russian archaeologists who continue to work at Denisova cave found a pierced pendant made from the tooth of a Siberian elk or wapiti during the 2019 field season. It was sent to Leipzig, where the palaeogenetics team had been trying to extract the DNA of whoever had worn personal artefacts found in French and Bulgarian caves. Their efforts had been unsuccessful, but such an object from Denisova clearly spurred them on. When someone wears next to the skin objects made of porous materials their sweat and the DNA that it carries seeps into the pores. If the materials decay very slowly, as do bone and especially teeth, genetic material can, in principle be extracted. But crushing up important ancient objects is not an option: for such rarities the extraction has to be non-destructive. It can only be done by ‘washing’ it in reagents that do not themselves break down DNA. Elena Essel and her many colleagues experimented with many ‘brews’ of reagents and repeated immersion at steadily rising temperature (up to 90°C). This releases genetic material in a stepwise fashion, allowing separation of contaminants in the host sediment from that which had penetrated into the tooth’s pores from whoever made the pendant and the wearer, and the animal from which it came

 Analysis of the recovered material yielded elk mtDNA, which was compared with that from four other ancient elks of known ages. This suggested that the elk had lived between 19 and 25 ka ago, thereby indirectly dating the time when the pendant was made and worn. A surprisingly large amount human DNA showed that the wearer was a female who was genetically allied with ancient anatomically modern humans who lived further east in Siberia at about that time.

Obviously this astonishing result opens up a wide vista for archaeology, though not from Palaeolithic burials, which are extremely rare. But artefacts of various kinds are much more common that actual human remains. Because the technique is non-destructive museums may be more willing to make objects in their collections available for analysis. Maybe the approach will be restricted to porous bone or tooth ornaments worn for long periods by individuals. Yet stone tools that were handled continually could be a more important target, depending on the rock from which they were made and its porosity.

See also: Lesté-Lasserre, C.. DNA from 25,000-year-old tooth pendant reveals woman who wore it. New Scientist, 3 May 2023.

Hydrogen and how the Earth formed

A third piece with hydrogen as its focus in a couple of months? Well, from a galactic perspective there’s a lot of it about. Modern cosmology suggests that only 4.6% of the energy in the universe consists of elemental atoms made of protons, neutrons and electrons, dwarfed by dark energy and dark matter that are something of mystery. But of the more familiar energy equivalent, tangible matter (as in E=mc2), 74% of the universe is hydrogen, 24% is helium and the other 92 elements amount to just 2%. That tiny proportion of heavier elements was created by nucleosynthesis within stars from the two products of the Big Bang (H and He). Nuclear fusion reactions formed those with atomic numbers (protons in their nuclei) up to that of iron (26), whereas the heavier elements were created through neutron- and proton capture when the largest stars destroyed themselves cataclysmically as supernovae. Yet the planet whose surface we inhabit contains only minute amounts of helium and elemental hydrogen. Of course water at and beneath the surface, in the form of atmospheric vapour and locked within minerals retains some of the cosmically available hydrogen. But current estimates suggest that hydrogen accounts for a mere 0.03% of Earth’s mass. Despite the fact that some forms of radioactive decay generate alpha particles that become helium it forms a vanishingly small proportion of terrestrial mass.

The solar system formed around 4.6 billion years ago by a complex gravitational accretion of the gas and dust of an interstellar cloud: mainly H and He. Its dynamic collapse resulted in gravitational potential energy being transformed into heat: in the case of the Sun, sufficient to set off self-sustaining nuclear fusion. As a body grows in this way so does its gravity and thus the speed needed for matter to escape from its pull (escape velocity). As temperature increases so does the speed at which atoms of each element vibrate; the lower the atomic mass the faster the vibration and the greater the chance of escape. So the ‘blend’ of elements that an astronomical body retains during its early evolution depends on its gravity and its surface temperature. The Sun is so massive that very little has escaped its pull, despite a surface temperature of about 5 to 6 thousand degrees Celsius. Its composition is thus close to the cosmic average. Those of the giant planets Jupiter, Saturn, Uranus and Neptune are not far short because of their large gravities and low surface temperatures. Even today, the smaller Inner Planets are unable to cling on to elemental hydrogen and helium and nearly all that is left of the matter from which they formed is the 2% of heavier cosmic elements locked into solids, liquids and gases.

Processes in the early solar system were far more complicated than they are today. In the mainly gaseous disc, from which the solar system evolved, gravity dragged matter towards its centre. That eventually ignited nuclear fusion of hydrogen to form our star. More remote from its gravitational pull vortices aggregated dust into bodies known as planetesimals that in turn accreted to larger protoplanets. Solar gravity dragged gas from the inner solar system leaving rocky protoplanets, whereas gas was able to be attracted to the surface of what became the gas giants where their gravity outweighed that of the far-off Sun. This was complicated by a sort of Milankovich Effect on steroids in which protoplanets continuously changed their orbits and underwent collisions. The best known of these was between the protoEarth and a Mars-sized body that formed the Earth-Moon system, both bodies having deep magma oceans as a result of the huge energy focussed on them by the collision. What may have happened to the protoplanet that became Earth before the Moon-forming collision has been addressed by three geoscientists at the University of California Los Angeles and the Carnegie Institution for Science Washington DC, USA (Young, E.D. et al. 2023. Earth shaped by primordial H2 atmospheres. Nature, v. 616, p. 306–311; DOI: 10.1038/s41586-023-05823-0 [PDF request to:]).

A thick hydrogen-rich atmosphere’s interacting chemically with a protoplanet (left). A possible later stage (right) where iron oxide in the magma ocean of the Early Hadean after Moon formation oxidises a hydrogen atmosphere to form surface water (Credit: Sean Raymond 2023, Fig 1)

The focus of the work of Edward Young, Anat Shahar and Hilke Schlichting is directed at the possibility that the Earth-forming protoplanets originally retained thick hydrogen atmospheres. They use thermodynamic modelling of the equilibrium between hydrogen and silicate magma oceans that had resulted from the energy of their accretion. The authors’ main assumption is that insufficient time had elapsed during accretion for the protoplanets to cool and crystallise: a distinct possibility because loss of accretionary heat by thermal radiation would have been ‘blanketed’ by actively accreting dust and gas in orbit around the growing protoplanets. Effectively, the equilibrium would have been chemical in nature: reactions between highly reducing hydrogen and oxidised silicate melts or even vaporised rock evaporated from the very hot surface. The authors suggest that protoplanets bigger than Mars (0.2 to 0.3 times that of Earth) could retain a hydrogen-rich atmosphere long enough for the chemical reactions to come to a balance, despite high temperatures. There would have been no shortage of hydrogen at this early stage in solar system evolution: perhaps as much as 0.2% percent the mass of the Earth surrounding a protoplanet about half its present size.

Two outcomes may have emerged. Reaction between hydrogen and anhydrous silicates could produce H2O in amounts up to three times that currently in the Earth’s oceans, some locked in the magma ocean, some in the dense atmosphere. A by-product would have been iron oxide, giving the current mantle its oxidising properties known from the geochemistry of basaltic magmas.  Hydrogen might also have dissolved in molten iron alloys, thereby contributing to the nascent core. That second outcome would help explain why the modern core is less dense than expected for iron-nickel alloy, both solid and liquid. In fact densities calculated by geophysicists from the speeds of seismic waves that have travelled through the core are 5 to 10% percent lower than expected for the alloy. So the core must contain substantial amounts of elements with low atomic numbers.

Several other possibilities have been suggested to account for Earth’s abundance of water. Two popular ideas are comets arriving in the ‘settled’ times of the Hadean or by original accretion of hydrous chondrite meteorites, whose hydrogen isotope proportions match those of ocean water. Hydrogen as the light element needed in the core is but one possibility along with oxygen, sulfur and other ‘light’ elements. Also, the oxidising potential of the modern mantle may have resulted from several billion years of wet lithosphere being subducted. To paraphrase Sean Raymond (below), ‘other hypotheses are available’!

See also: Raymond, S.N. 2023. Earth’s molten youth had long-lasting consequences. Nature (News & Views), v. 616, p. 251-252; DOI: 10.1038/d41586-023-00979-1 [PDF request to:]

The Moon may have water resources in its soil

Apart from signs of water ice in permanently shadowed areas of some polar craters, the Moon’s surface has generally been considered to be very dry. Rocks returned by the various Apollo missions contain minute traces of water by comparison with similar rocks on Earth. They consist only of anhydrous minerals such as feldspars, pyroxenes and olivines. But much of the lunar surface is coated by regolith: a jumble of rock fragments and dust ejected from a vast number of impact craters over billions of years. It is estimated to be between 3 and 12 m deep. Much of the finer grained regolith is made up of silicate-glass spherules created by the most powerful impacts.

The lunar regolith at Tranquillity Base bearing an astronaut’s bootprint (Credit: Buzz Aldrin, NASA Apollo 11, Photo ID AS11-40-5877)

The scientific and economic (i.e. mining) impetus for the establishment of long term human habitation on the lunar surface hangs on the possibility of extracting water from the Moon itself. It is needed for human consumption and as a source through electrolysis of both oxygen and hydrogen for breathing and also for rocket fuel. The stupendous cost, in both monetary and energy terms, of shifting mass from Earth to the Moon clearly demands self-sufficiency in water for a lunar base occupied for more than a few weeks.

Remote sensing that focussed on the ability of water molecules and hydroxyl (OH) ions to absorb solar radiation with a wavelength of 2.8 to 3.0 micrometres was deployed by the Indian lunar orbiter Chandrayaan-1 that collected data for several months in 2008-9. The results suggested that OH and H2O were detectable over a large proportion of the lunar surface at concentrations estimated at between 10 parts per million (ppm) up to about 0.1%. Where did these hydroxyl ions and water molecules come from and what had locked them up? There are several possibilities for their origin: volcanic activity that tapped the Moon’s mantle (magma could not have formed had some water not been present at great depths); impacts of icy bodies such as comets; even the solar wind that carries protons, i.e. hydrogen atoms stripped of their electrons. Conceivably, protons could react with oxygen in silicate material at the surface to produce both OH and H2O to be locked within solid particles. To assess the possibilities a group of researchers at Chinese and British institutions have examined in detail the 1.7 kg of lunar-surface materials collected and returned to Earth by the 2020 Chinese Chang’e 5 lunar sample return mission (He, H. and 27 others 2023. A solar wind-derived water reservoir on the Moon hosted by impact glass beads. Nature Geoscience, online article; DOI: 10.1038/s41561-023-01159-6)

He et al. focussed on glass spherules formed by impact melting of lunar basalts, whose bulk composition they retain. The glass ‘beads’ contain up to 0.2 % water, mainly concentrated in their outermost parts. This alone suggests that the water and hydroxyl ions were formed by spherules being bathed in the solar wind rather than being of volcanic or cometary origin and trapped in the glass. An abnormally low proportion of deuterium (2H) relative to the more abundant 1H isotope of hydrogen in the spherules is consistent with that hypothesis. Indeed, the high temperatures involved in impact melting would be expected to have driven out any ‘indigenous’ water in the source rocks. The water and OH ions seem to have built up over time, diffusing into the glass from their surfaces rather than gradually escaping from within.

An awful lot of regolith coats the lunar surface, as many of the images taken by the Apollo astronauts amply show. So how much water might be available from the lunar regolith? The Chinese-British team reckon between 3.0 × 108 to 3.0 × 1011 metric tons. But how much can feasibly be extracted at a lunar base camp? The data suggest that a cubic metre (~2 t) of regolith could yield enough to fill 4 shot glasses (~0.13 litres). Using a solar furnace and a condenser – the one in full sunlight the other in the shade – is not, as they say, ‘rocket science’. But for a minimum 3 litres per day intake of fluids per person, a team of 4 astronauts would need to shift and process roughly 100 m3 of regolith every day. Over a year, this would produce a substantial pit. But that assumes all the regolith contains some water, yet the data are derived from the surface alone …See also:Glass beads on moon’s surface may hold billions of tonnes of water, scientists say. The Guardian, 27 March 2023.

How humans might have migrated into the Americas

When and how humans first migrated into the Americas are issues that have exercised anthropologists for the last two decades, often sparking off acrimonious debate. In the 20th century both seemed to well established: hunters using the celebrated Clovis fluted spear blades arrived first, no earlier than 13 ka ago. The Beringia land bridge across what is now the Bering Strait was exposed by falling sea level as early as 30 thousand years ago in the lead-up to the last glacial maximum (LGM) to link eastern Siberia and Alaska. However, ice sheets expanding to the south-west of the main area of glaciation on the Canadian Shield barred passage through Interior Alaska and NW Canada. Only around 13 ka had a N-S ice-free corridor opened through the mountains during glacial retreat. Nevertheless, humans had entered Alaska at least ten thousand years earlier, during the LGM, to occupy caves in its western extremity: Alaska was habitable but they were stuck there.

In the early 21st century, it became clear that the ‘Clovis First’ hypothesis was mistaken. Sediments in Texas that contained Clovis blades were found to be underlain by those of an older culture, reliably dated to about 15.5 ka. Furthermore, analysis of the DNA of all groups of native Americans (north and south) indicated a last common ancestor in Siberia more than 30 ka ago: they descended from that ancestor outside of Asia. More recently excavated sites in Mexico and Chile point to human populations having reached there as early at 33 ka (see: Earliest Americans, and plenty of them; July 2020), and there is a host of pre-Clovis sites in North and Central America dating back to 18.2 ka. Such ancient groups could not have walked from the Beringia land bridge because the present topographic grain in the Western Cordillera would have been blocked by ice since about 25 thousand years ago. The only viable possibility was that they followed the Alaskan coast to move southwards, either in boats or over sea ice.

Dated pre-Clovis sites in Mexico and North America and possible expanding distribution of people from 31.3 to 14.2 ka (Credit; Becerra-Valdivia and Higham; Extended Data Fig. 4)

A new focus on when such journeys would have been feasible was published in February 2023 (Praetorius, S.K et al. 2023. Ice and ocean constraints on early human migrations into North America along the Pacific coast. Proceedings of the National Academy of Science, v. 120, article e2208738120; DOI: 10.1073/pnas.2208738120). One advantage of moving along the coast is that, though it would be pretty cold, the warming effect of the Pacific Ocean would make it more bearable than travelling inland, where winter temperatures even today regularly reach -50°C. More important, there would be no shortage of food; fish, marine mammals and shellfish abound at the ice margin or onshore, at any season. But a coastal route may not have been possible at all times during the period either side of the LGM. Large glaciers still reach the ocean from Alaska and there is little more perilous than crossing the huge crevasse fields that they present. Boating would have been highly dangerous because of continual calving of icebergs from extensive ice shelves. Moreover, the Alaska Coastal Current flows northwards and would likely have sped up during episodes of glacial melting as the current is affected by fresh water influx. Yet there may sometimes have been episodes of open water at the ice front frozen to relatively flat sea ice in winter. That would making boat- or foot travel relatively safe. Sea ice would also make glacier-free islands accessible for encampments over the harsh winters or even for hundreds of years, with plenty of marine food resources.

Summer Praetorius of the US Geological Survey and colleagues from Woods Hole Oceanographic Institution, Oregon State University, and the Universities of California (Santa Cruz) and Oregon have attempted to model conditions since 32.5 ka ago in coastal waters off Northwest America. They used simulations of the behaviour of the Alaska Coastal Current during varying climate conditions before and during the LGM, while glaciers were in  retreat that followed and during the Holocene. Their modelling is based on the effects of changing sea level and water salinity on general circulation in the Northern Pacific. The relative abundance of sea ice can be tracked using variation in an alkenone produced by phytoplankton that wax and wane according to sea-surface temperature and sea-ice cover. The other input is the well-documented changing extent of continental glaciation in Alaska and the Yukon Territory. Based on their model they estimate that the most favourable environmental conditions for coastal migration occurred just before the LGM (24.5 to 22 ka) and between 16.4 and 14.8 ka during the initial stages of warming and extensive melting of ice sheets. The Alaskan Coastal Current probably doubled in intensity during the LGM making the use of boats highly dangerous

By 35 ka ocean-going boats are known to have been used by people in northern Japan. Traversing sea-ice was the way in which Inuit people occupied all the Arctic coastal areas of North America and Greenland during the last five thousand years, and is the form of travel favoured by the authors. It is not yet possible to prove and date such coastal journeys because campsites or settlements along the coast would now be inundated by 100 m of post-glacial sea-level rise. Yet such migration was necessary to establish settlements at lower latitudes in North America and Mexico in the period when overland routes from Beringia were blocked by ice sheets. By 32.5 ka falling sea level probably made it possible to cross the Bering Strait for the first time and for the next 7.5 ka an ice-free corridor made it possible for the rest of North America and points further south to be reached on-foot from Alaska. That window of opportunity might have allowed humans to have reached Mexico and South America, where the earliest dates of occupation have been found. But many of the early sites across North America date to the period (25 to 13 ka) when overland access was blocked. Of course, those sites might have been established by expansion from the very earliest migrants who crossed the Beringia land bridge and took advantage of overland passage before 25 ka. But if later migrants from Asia could follow the coastal route, then it seems likely that they did. Later Inuit spread along  the shores of the Arctic Ocean since 5000 years ago probably with a material culture little different from that of the earlier migrants from Siberia.

Naturally occurring hydrogen: an abundant green fuel?

Burning hydrogen produces only water vapour, so it is not surprising that it has been touted as the ultimate ‘green’ energy source, and increasingly attracts the view that the ‘Hydrogen Economy’ may replace that based on fossil fuels. It is currently produced from natural gas by ‘steam reforming’ of methane that transforms water vapour and CH4 to hydrogen and carbon monoxide. That clearly doesn’t make use of the hydrogen ‘green’ as the CO becomes carbon dioxide because it reacts with atmospheric oxygen; it is termed ‘grey hydrogen’. But should it prove possible to capture CO and store it permanently underground in some way then that can be touted as ‘blue hydrogen’ thereby covering up the carbon footprint of all the rigmarole in getting the waste CO into a safe reservoir. However, if carbon-free electricity from renewables is used to electrolyse water into H and O the hydrogen aficionados can safely call it ‘green hydrogen’.   It seem there is a bewildering colour coding for hydrogen that depends on the various options for its production: ‘yellow’ if produced using solar energy; ‘red’ if made chemically from biowaste; ‘black’ by coking coal using steam; ‘pink’ is electrolysis using nuclear power; and even ‘turquoise’ hydrogen if methane is somehow turned into hydrogen and solid carbon using renewables – a yet-to-be-developed technology! Very jolly but confusing: almost suspiciously so!

But not to be forgotten is the ‘white’ variety, applied to hydrogen that is emitted by natural processes within the Earth. Eric Hand, the European news editor for the major journal Science has written an excellent Feature article about ‘white’ hydrogen in a recent issue (Hand, E. 2023. Hidden hydrogen. Science, v. 379, article adh1460; DOI: 10.1126/science.adh1460). Hand’s feature is quirky, but well-worth a read. It is based on the proceedings of a Geological Society of America mini-conference about non-petroleum, geological energy resources  held in October 2022. He opens with a bizarre anecdote related by a farmer who lives in rural Mali. The only drilling that ever went on in his village was for water, and many holes were dry. But one attempt resulted in ‘wind coming out of the hole’. When a driller looked in the hole, the ‘wind’ burst into flame – he had a cigarette in his mouth. The fire burned for months. Some 20 years later the story reached a Malian company executive who began prospecting the area’s petroleum potential, believing the drilling had hit natural gas. Analysis of the gas revealed that it was 98% hydrogen – now the village has electricity generated by ‘white’ hydrogen.

Mantle rock in the Oman ophiolite, showing cores of fresh peridotite, surrounded by brownish serpentinite and white magnesium carbonate veins (credit: Juerg Matter, Oman Drilling Project, Southampton University, UK)

So how is hydrogen produced by geological processes? Some springs in the mountains of Oman also release copious amounts of the gas. The springs emerge from ultramafic rocks of the vast ophiolite that was emplaced onto the Arabian continental crust towards the end of the Cretaceous. The lower part of this obducted mass of oceanic lithosphere is mantle rock dominated by iron- and magnesium-rich silicates, mainly olivine [(Mg,Fe)2SiO4 – a solid solution of magnesium and iron end members]. When saturated with groundwater in which CO2 is dissolved olivine breaks down slowly but relentlessly. The hydration reaction is exothermic and generates heat, so is self-sustaining. Olivine’s magnesium end member is hydrated to form the soft ornamental mineral serpentine (Mg3Si2O5(OH)4) and magnesium carbonate. Under reducing conditions the iron end member reacts with water to produce an iron oxide, silica and hydrogen:

3Fe2SiO4 + 2H2O → 2 Fe3O4 + 3SiO­2 +3H2

Gases emanating from mid-ocean ridges contain high amounts of hydrogen produced in this way, for example from Icelandic geothermal wells. But Mali is part of an ancient craton, so similar reactions involving iron-rich ultramafic rocks deep in the continental crust are probably sourcing hydrogen in this way too. Hydrogen production on the scale of that discovered in Mali seems to be widespread, with discoveries in Australia, the US, Brazil and the Spanish Pyrenees that have pilot-scale production plants. The US Geological Survey has estimated that around 1 trillion tonnes of ‘white’ hydrogen may be available for extraction and use

Hydrogen, like other natural gases, may be trapped below the surface in the same ways as in commercial petroleum fields. But petroleum-gas wells emit little if any hydrogen mixed in with methane. That absence is probably because petroleum fields occur in deep sedimentary basins well above any crystalline basement. The geophysical exploration that discovers and defines the traps in petroleum fields has never been deployed over areas of crystalline continental crust because as far as the oil companies are concerned they are barren. That may be about to change. There is another exploration approach: known hydrogen seepage seems to deter vegetation so that the sites are in areas of bare ground, which have been called ‘fairy circles’. These could be detected easily using remote sensing techniques.

Artificially increasing serpentine formation by pumping water into the mantle part of ophiolites, such as that in Oman, and other near-surface ultramafic rocks is also a means of carbon sequestration, which should produce hydrogen as a by-product (see: Global warming: Can mantle rocks reduce the greenhouse effect?, July 2021). A ‘two-for-the-price-of-one’ opportunity?

Who invented stone tools? A great surprise from Kenya

Up to now the earliest stone tools are objects dated to about 3.3 Ma (Late Pliocene) found in the Turkana basin of Kenya in 2015. They are sharp-edged pieces of rock that seem to have been made simply by striking two lumps of rock together (see: Stone tools go even further back; May 2015). These Lomekwian artefacts are similar to the basic tools made today by some chimpanzees in parts of Africa. Their age matches that for the earliest known animal bones that show signs of having meat cut from them, which were unearthed in Dikika, Ethiopia (see: Another big surprise; September 2010) which, like the Lomekwian tools, are not accompanied by tools or hominin remains. The earliest tools associated with members of the genus Homo are significantly more sophisticated. They were found in close association with H. habilis at what seems to have been a well-used butchering site, dated at 2.0 Ma, in Tanzania’s Olduvai Gorge, hence their designation as the Oldowan ‘industry’. The Oldowan ‘tool kit’ includes choppers and blades deliberately shaped to be wielded by hand and made by striking large cobbles with distinctive hammer stones. Earlier tools with this level of deliberate crafting come from the 2.6 Ma Ledi-Geraru site in the Afar Depression of NE Ethiopia but with no sign of their makers.

Oldowan tools used for pounding and cutting from Nyayanga, Kenya (Credit: Thomas Plummer, James Oliver and Emma Finestone/Homa Peninsula Paleoanthropology Project/SWNS)

The presence of Oldowan tools has now been pushed further back, by about 400 ka, thanks to excavations in Late Pliocene sediments at Nyayanga on the shore of Lake Victoria in western Kenya by Thomas Plummer of Queens College in New York State, USA, and his numerous collaborators from the US, Germany, the UK, China, Italy, Australia, Kenya, South Africa and Poland (Plummer, T.W. and 31 others 2023. Expanded geographic distribution and dietary strategies of the earliest Oldowan hominins and Paranthropus. Science, v. 379, p. 561-566; DOI: 10.1126/science.abo7452). Their work also expands the range of Oldowan culture by about 1300 km. The Nyayanga site yielded over 300 artefacts that closely resemble the previously known range of Oldowan tool shapes. Their makers struck flakes from suitable corestones – made of rhyolite, quartz and quartzite – and trimmed them by more intricate means. They seem to have been used to cut up mainly hippo and buffalo, bones of which bear clear cut marks, but had other uses. Analysis of the wear on tool surfaces not only show signs of butchery, but also processing of plant tissue by pounding; the latter resulted in pitting and polishing of tools that seem to have been used many times. Stable-isotope analysis of the bones and animal teeth suggests that in the Pliocene Nyayanga was a grassy and partly wooded savannah close to a substantial water body needed by hippos.

Reconstruction of a Paranthropus head (Credit: Jerry Humphrey, Pinterest)

The ‘great surprise’ is that the only hominin remains associated with the site are two damaged molar teeth. They are so large that their most likely source was a species of Paranthropus.Paranthropoids have long been considered to be a gorilla-like, ‘robust’ branch of australopithecines. Their large cranial crests anchoring jaw muscles and enormous teeth were reckoned to indicate a diet of tough vegetation – the discoverer of the first specimen of P. boisei dubbed it ‘Nutcracker Man’ – although the wear on individual teeth suggests otherwise. But there is no reason to suppose that they could not eat meat. They survived australopithecines by more than a million years to cohabit the East African savannahs with H. ergaster until about 1 Ma ago.

Lead author Thomas Plummer wonders if paranthropoids would have needed tools because they had the largest jaws and teeth of any hominin. But had his team found close association with smaller H.habilis teeth would he have held a similarly negative view? There is evidence from younger sites in South Africa that paranthropoids used a wide diversity of bone tools and may even have been among the earliest fire users. So why the negativity about stone tools? To paraphrase Ali G, ‘Is it because they is ugly?’

See also: Devlin, H, Discovery of 3m-year-old stone tools sparks prehistoric whodunit. The Guardian, 9 February 2023