geology

saturn’s-moon-titan-has-shorelines-that-appear-to-be-shaped-by-waves

Saturn’s moon Titan has shorelines that appear to be shaped by waves

astronomy, Cassini, geology, planetary science, Saturn, Science, Titan / /

Surf the moon —

The liquid hydrocarbon waves would likely reach a height of a meter.

–

Ligeia Mare, the second-largest body of liquid hydrocarbons on Titan.

Enlarge / Ligeia Mare, the second-largest body of liquid hydrocarbons on Titan.

During its T85 Titan flyby on July 24, 2012, the Cassini spacecraft registered an unexpectedly bright reflection on the surface of the lake Kivu Lacus. Its Visual and Infrared Mapping Spectrometer (VIMS) data was interpreted as a roughness on the methane-ethane lake, which could have been a sign of mudflats, surfacing bubbles, or waves.

“Our landscape evolution models show that the shorelines on Titan are most consistent with Earth lakes that have been eroded by waves,” says Rose Palermo, a coastal geomorphologist at St. Petersburg Coastal and Marine Science Center, who led the study investigating signatures of wave erosion on Titan. The evidence of waves is still inconclusive, but future crewed missions to Titan should probably pack some surfboards just in case.

Troubled seas

While waves have been considered the most plausible explanation for reflections visible in Cassini’s VIMS imagery for quite some time, other studies aimed to confirm their presence found no wave activity at all. “Other observations show that the liquid surfaces have been very still in the past, very flat,” Palermo says. “A possible explanation for this is at the time we were observing Titan, the winds were pretty low, so there weren’t many waves at that time. To confirm waves, we would need to have better resolution data,” she adds.

The problem is that this higher-resolution data isn’t coming our way anytime soon. Dragonfly, the next mission to Titan, isn’t supposed to arrive until 2034, even if everything goes as planned.

To get a better idea about possible waves on Titan a bit sooner, Palermo’s team went for inferring their presence from indirect cues. The researchers assumed shorelines on Titan could have been shaped by one of three candidate scenarios. They first assumed there was no erosion at all; the second modeled uniform erosion caused by the dissolution of the bedrock by the ethane-methane liquid; and the third assumed erosion by wave activity. “We took a random topography with rivers, filled up the basin-flooding river valleys all around the lake. Then, we then used landscape evolution computer model to erode the coast to 50 percent of its original size,” Palermo explains.

Sizing the waves

Palermo’s simulations showed that wave erosion resulted in coastline shapes closely matching those actually observed on Titan.

The team validated its model using data from closer to home. “We compared using the same statistical analysis to lakes on Earth, where we know what the erosion processes are. With certainty greater than 77.5 percent, we were able to predict those known processes with our modeling,” Palermo says.

But even the study that claimed there were waves visible in the Cassini’s VIMS imagery concluded they were roughly 2 centimeters high at best. So even if there are waves on Titan, the question is how high and strong are they?

According to Palermo, wave-generation mechanisms on Titan should work just like they do on Earth, with some notable differences. “There is a difference in viscosity between water on Earth and methane-ethane liquid on Titan compared to the atmosphere,” says Palermo. The gravity is also a lot weaker, standing at only one-seventh of the gravity on Earth. “The gravity, along with the differences in material properties, contributes to the waves being taller and steeper than those on Earth for the same wind speed,” says Palermo.

But even with those boosts to size and strength, could waves on Titan actually be any good for surfing?

Surf’s up

“There are definitely a lot of open questions our work leads to. What is the direction of the dominant waves? Knowing that can tell us about the winds and, therefore, about the climate on Titan. How large do the waves get? In the future, maybe we could tell that with modeling how much erosion occurs in one part of the lake versus another in estimated timescales. There is a lot more we could learn,” Palermo says. As far as surfing is concerned, she said that, assuming a minimum height for a surfable wave of around 15 centimeters, surfing on Titan should most likely be doable.

The key limit on the size and strength of any waves on Titan is that most of its seas are roughly the size of the Great Lakes in the US. The largest of them, the Kraken Mare, is roughly as large as the Caspian Sea on Earth. There is no such thing as a global ocean on Titan, and this means the fetch, the distance over which the wind can blow and grow the waves, is limited to tens of kilometers instead of over 1,500 kilometers on Earth. “Still, some models show that the waves on Titan be as high as one meter. I’d say that’s a surfable wave,” Palermo concluded.

Saturn’s moon Titan has shorelines that appear to be shaped by waves Read More »

east-coast-has-a-giant-offshore-freshwater-aquifer—how-did-it-get-there?

East Coast has a giant offshore freshwater aquifer—how did it get there?

aquifers, Earth science, fresh water, geology, glaciers, Science / /
Image of a large boat with a tall tower at its center, and a crane in the rear. It is floating on a dark blue ocean and set in front of a white cloud.

Enlarge / An oceangoing scientific drilling vessel may be needed to figure out how huge undersea aquifers formed.

One-quarter of the world’s population is currently water-stressed, using up almost their entire fresh water supply each year. The UN predicts that by 2030, this will climb to two-thirds of the population.

Freshwater is perhaps the world’s most essential resource, but climate change is enhancing its scarcity. An unexpected source may have the potential to provide some relief: offshore aquifers, giant undersea bodies of rock or sediment that hold and transport freshwater. But researchers don’t know how the water gets there, a question that needs to be resolved if we want to understand how to manage the water stored in them.

For decades, scientists have known about an aquifer off the US East Coast. It stretches from Martha’s Vineyard to New Jersey and holds almost as much water as two Lake Ontarios. Research presented at the American Geophysical Union conference in December attempted to explain where the water came from—a key step in finding out where other undersea aquifers lie hidden around the world.

As we discover and study more of them, offshore aquifers might become an unlikely resource for drinking water. Learning the water’s source can tell us if these freshwater reserves rebuild slowly over time or are a one-time-only emergency supply.

Reconstructing history

When ice sheets sat along the East Coast and the sea level was significantly lower than it is today, the coastline was around 100 kilometers further out to sea. Over time, freshwater filled small pockets in the open, sandy ground. Then, 10,000 years ago, the planet warmed, and sea levels rose, trapping the freshwater in the giant Continental Shelf Aquifer. But how that water came to be on the continental shelf in the first place is a mystery.

New Mexico Institute of Mining and Technology paleo-hydrogeologist Mark Person has been studying the aquifer since 1991. In the past three decades, he said, scientists’ understanding of the aquifer’s size, volume, and age has massively expanded. But they haven’t yet nailed down the water’s source, which could reveal where other submerged aquifers are hiding—if we learn the conditions that filled this one, we could look for other locations that had similar conditions.

“We can’t reenact Earth history,” Person said. Without the ability to conduct controlled experiments, scientists often resort to modeling to determine how geological structures formed millions of years ago. “It’s sort of like forensic workers looking at a crime scene,” he said.

Person developed three two-dimensional models of the offshore aquifer using seismic data and sediment and water samples from boreholes drilled onshore. Two models involved ice sheets melting; one did not.

Then, to corroborate the models, Person turned to isotopes—atoms with the same number of protons but different numbers of neutrons. Water mostly contains Oxygen-16, a lighter form of oxygen with two fewer neutrons than Oxygen-18.

Throughout the last million years, a cycle of planetary warming and cooling occurred every 100,000 years. During warming, the lighter 16O in the oceans evaporated into the atmosphere at a higher rate than the heavier 18O. During cooling, that lighter oxygen came down as snow, forming ice sheets with lower levels of 18O and leaving behind oceans with higher levels of 18O.

To determine if ice sheets played a role in forming the Continental Shelf Aquifer, Person explained, you have to look for water that is depleted in 18O—a sure sign that it came from ice sheets melting at their base. Person’s team used existing global isotope records from the shells of deep-ocean-dwelling animals near the aquifer. (The shells contain carbonate, an ion that includes oxygen pulled from the water).

Person then incorporated methods developed by a Columbia graduate student in 2019 that involve using electromagnetic imaging to finely map undersea aquifers. Since saltwater is more electrically conductive than freshwater, the boundaries between the two kinds of water are clear when electromagnetic pulses are sent through the seafloor: saltwater conducts the signal well, and freshwater doesn’t. What results looks sort of like a heat map, showing regions where fresh and saltwater are concentrated.

Person compared the electromagnetic and isotope data with his models to see which historical scenarios (ice or no ice) were statistically likely to form an aquifer that matched all the data. His results, which are in the review stage with the Geological Society of America Bulletin, suggest it’s very likely that ice sheets played a role in forming the aquifer.

“There’s a lot of uncertainty,” Person said, but “it’s the best thing we have going.”

East Coast has a giant offshore freshwater aquifer—how did it get there? Read More »

renovation-relic:-man-finds-hominin-jawbone-in-parents’-travertine-kitchen-tile

Renovation relic: Man finds hominin jawbone in parents’ travertine kitchen tile

Archaeology, fossils, geology, Hominin, human fossils, Science / /

Kitchen reno surprise —

Yes, travertine often has embedded fossils. But not usually hominin ones.

–

closeup of fossilized jawbone in a piece of travertine tile

Enlarge / Reddit user Kidipadeli75 spotted a fossilized hominin jawbone in his parents’ new travertine kitchen tile.

Reddit user Kidipadeli75

Ah, Reddit! It’s a constant source of amazing stories that sound too good to be true… and yet! The latest example comes to us from a user named Kidipadeli75, a dentist who visited his parents after the latter’s kitchen renovation and noticed what appeared to be a human-like jawbone embedded in the new travertine tile. Naturally, he posted a photograph to Reddit seeking advice and input. And Reddit was happy to oblige.

User MAJOR_Blarg, for instance, is a dentist “with forensic odontology training” and offered the following:

While all old-world monkeys, apes, and hominids share the same dental formula, 2-1-2-3, and the individual molars and premolars can look similar, the specific spacing in the mandible itself is very specifically and characteristically human, or at least related and very recent hominid relative/ancestor. Most likely human given the success of the proliferation of H.s. and the (relatively) rapid formation of travertine.

Against modern Homo sapiens, which may not be entirely relevant, the morphology of the mandible is likely not northern European, but more similar to African, middle Eastern, mainland Asian.

Another user, deamatrona, who claims to hold an anthropology degree, also thought the dentition looked Asiatic, “which could be a significant find.” The thread also drew the attention of John Hawks, an anthropologist at the University of Wisconsin–Madison and longtime science blogger who provided some valuable context on his own website. (Hawks has been involved with the team that discovered Homo naledi at the Rising Star cave system in 2013.)

For instance, much of the appeal of natural stone like travertine for home decor is its imperfections. But who knew that it’s actually quite common to find embedded fossils? It’s rarer to find hominin fossils but not unprecedented. Hawks specifically mentioned a quarry site near Bilzingsleben, Germany, where an archaeologist named Dietrich Mania discovered parts of two humans skulls and a mandible dating as far back as 470,000 years. And a hominin cranium was found in 2002 in a travertine quarry in southwestern Turkey. It was later dated to between 1.2 million and 1.6 million years old.

The obvious question—asked by numerous Redditors— is how one could possibly install all that kitchen tile without noticing a fossilized human jawbone in the travertine. Hawks offered a reasonable answer:

Quarries rough-cut travertine and other decorative stone into large panels, doing basic quality checks for gaps and large defects on the rough stone before polishing. Small defects and inclusions are the reason why people want travertine in the first place, so they don’t merit special attention. Consumers who buy travertine usually browse samples in a showroom to choose the type of rock, and they don’t see the actual panels or tile until installation. Tile or panels that are polished by machine and stacked in a workshop or factory for shipping are handled pretty quickly.

What this means is that there may be lots more hominin bones in people’s floors and showers.

Most will be hard to recognize. Random cross-sections of hominin bones are tough to make out from other kinds of fossils without a lot of training. Noticing a fossil is not so hard, but I have to say that I’ve often been surprised at what the rest of a fossil looks like after skilled preparators painstakingly extract it from the surrounding rock. The ways that either nature or a masonry saw may slice a fossil don’t correspond to an anatomy book, and a cross-section through part of a bone doesn’t usually resemble an X-ray image of a whole bone.

Cue a horde of amateur fossil enthusiasts excitedly scouring their travertine for signs of important archaeological finds.

But as Hawks notes, chances are that one wouldn’t be able to clearly identify a fossil even if it was embedded in one’s tile, given how thin such tiles and panels are typically cut. And one is far more likely to find fossils of algae, plants, mollusks, crustaceans, or similar smaller creatures than human remains. “Believe me, anthropologists don’t want to hear about every blob of bone in your tile,” Hawks wrote. “But certainly somebody has more pieces of the mandible of the Reddit post.”

Kidipadeli75 posted an update to the Reddit thread providing a few more details, such as that he and his parents live in Europe. He’s also pretty sure the mandible doesn’t belong to Jimmy Hoffa. While Kidipadeli75 originally thought the quarry of origin was in Spain, it is actually located in Turkey—just like the hominin cranium found near Kocabaş in 2002. The story is still developing, given that several researchers have already contacted Kidipadeli75 for more information and to offer their expertise. The bone might turn out to be very old indeed and potentially a scientifically significant find.

Could a new HGTV series be far behind? Renovation Relics, perhaps, or Fossil Fixer-Upper.  Feel free to pitch your own show ideas in the comments.

Renovation relic: Man finds hominin jawbone in parents’ travertine kitchen tile Read More »

tiny-cracks-in-rocks-may-have-concentrated-chemicals-needed-for-life

Tiny cracks in rocks may have concentrated chemicals needed for life

biochemistry, Biology, chemistry, geology, origin of life, Science / /
Cartoon of a geologically active area, showing sub-surface channels in different colors to represent various temperatures.

Enlarge / Active geology could have helped purify key chemicals needed for life.

Christof B. Mast

In some ways, the origin of life is looking much less mystifying than it was a few decades ago. Researchers have figured out how some of the fundamental molecules needed for life can form via reactions that start with extremely simple chemicals that were likely to have been present on the early Earth. (We’ve covered at least one of many examples of this sort of work.)

But that research has led to somewhat subtler but no less challenging questions. While these reactions will form key components of DNA and protein, those are often just one part of a complicated mix of reaction products. And often, to get something truly biologically relevant, they’ll have to react with some other molecules, each of which is part of its own complicated mix of reaction products. By the time these are all brought together, the key molecules may only represent a tiny fraction of the total list of chemicals present.

So, forming a more life-like chemistry still seems like a challenge. But a group of German chemists is now suggesting that the Earth itself provides a solution. Warm fluids moving through tiny fissures in rocks can potentially separate out mixes of chemicals, enriching some individual chemicals by three orders of magnitude.

Feeling the heat (and the solvent)

Even in the lab, it’s relatively rare for chemical reactions to produce just a single product. But there are lots of ways to purify out exactly what you want. Even closely related chemicals will often differ in their solubility in different solvents and in their tendency to stick to various glasses or ceramics, etc. The temperature can also influence all of those. So, chemists can use these properties as tools to fish a specific chemical out of a reaction mixture.

But, as far as the history of life is concerned, chemists are a relatively recent development—they weren’t available to purify important chemicals back before life had gotten started. Which raises the question of how the chemical building blocks of life ever reached the sorts of concentrations needed to do anything interesting.

The key insight behind this new work is that something similar to lab equipment exists naturally on Earth. Many rocks are laced with cracks, channels, and fissures that allow fluid to flow through them. In geologically active areas, that fluid is often warm, creating temperature gradients as it flows away from the heat source. And, as fluid moves through different rock types, the chemical environment changes. The walls of the fissures will have different chemical properties, and different salts may end up dissolved in the fluid.

All of that can provide conditions where some chemicals move more rapidly through the fluid, while others tend to stay where they started. And that has the potential to separate out key chemicals from the reaction mixes that produce the components of life.

But having the potential is very different from clearly working. So, the researchers decided to put the idea to the test.

Tiny cracks in rocks may have concentrated chemicals needed for life Read More »

webb-telescope-spots-hints-that-eris,-makemake-are-geologically-active

Webb telescope spots hints that Eris, Makemake are geologically active

astronomy, dwarf planet, Eris, geology, Kuiper belt, Makemake, planetary science, Science / /
Image of two small planets, one more reddish, the second very white.

Enlarge / Artist’s conceptions of what the surfaces of two dwarf planets might look like.

Active geology—and the large-scale chemistry it can drive—requires significant amounts of heat. Dwarf planets near the far edges of the Solar System, like Pluto and other Kuiper Belt objects, formed from frigid, icy materials and have generally never transited close enough to the Sun to warm up considerably. Any heat left over from their formation was likely long since lost to space.

Yet Pluto turned out to be a world rich in geological features, some of which implied ongoing resurfacing of the dwarf planet’s surface. Last week, researchers reported that the same might be true for other dwarf planets in the Kuiper Belt. Indications come thanks to the capabilities of the Webb telescope, which was able to resolve differences in the hydrogen isotopes found on the chemicals that populate the surface of Eris and Makemake.

Cold and distant

Kuiper Belt objects are natives of the distant Solar System, forming far enough from the warmth of the Sun that many materials that are gasses in the inner planets—things like nitrogen, methane, and carbon dioxide—are solid ices. Many of these bodies formed far enough from the gravitational influence of the eight major planets that they have never made a trip into the warmer inner Solar System. In addition, because there was much less material that far from the Sun, most of the bodies are quite small.

While they would have started off hot due to the process by which they formed, their small size means a large surface-to-volume ratio, allowing internal heat to radiate out to space relatively quickly. Since then, any heat has come from rare collision events or the decay of radioactive isotopes.

Yet New Horizons’ visit to Pluto made it clear that it doesn’t take much heat to drive active geology, although seasonal changes in sunlight are likely to account for some of its features. Sunlight is less likely to be an influence for worlds like Makemake, which orbits at a distance one and a half times Pluto’s closest approach to the Sun. Eris, which is nearly as large as Pluto, orbits at over twice Pluto’s closest approach.

Sending a mission to either of these planets would take decades, and none are in development at the moment, so we can’t know what their surfaces look like. But that doesn’t mean we know nothing about them. And the James Webb Space Telescope has added to what we know considerably.

The Webb was used to image sunlight reflected off these objects, obtaining its infrared spectrum—the amount of light reflected at different wavelengths. The spectrum is influenced by the chemical composition of the dwarf planets’ surfaces. Certain chemicals can absorb specific wavelengths of infrared light, ensuring they don’t get reflected. By noting where the spectrum dips, it’s possible to figure out which chemicals are present.

Some of that work has already been done. But Webb is able to image parts of the spectrum that were inaccessible earlier, and its instruments are even able to identify different isotopes of the atoms composing each chemical. For example, some molecules of methane (CH4) will, at random, have one of their hydrogen atoms swapped out for its heavier isotope, deuterium, forming CH3D. These isotopes can potentially act as tracers, telling us things about where the chemicals originally came from.

Webb telescope spots hints that Eris, Makemake are geologically active Read More »

it’s-a-fake:-mysterious-280-million-year-old-fossil-is-mostly-just-black-paint

It’s a fake: Mysterious 280 million-year-old fossil is mostly just black paint

Archaeology, forgeries, fossils, geology, paleontology, Science, Tridentinosaurus antiquus / /

A cautionary tale —

The long bones of the hind limbs appear to be genuine. The rest? Not so much.

–

image of a reptilian fossil in a rock

Enlarge / Discovered in 1931, Tridentinosaurus antiquus has now been found to be, in part, a forgery.

Valentina Rossi

For more than 90 years, scientists have puzzled over an unusual 280 million-year-old reptilian fossil discovered in the Italian Alps. It’s unusual because the skeleton is surrounded by a dark outline, long believed to be rarely preserved soft tissue. Alas, a fresh analysis employing a suite of cutting-edge techniques concluded that the dark outline is actually just bone-black paint. The fossil is a fake, according to a new paper published in the journal Paleontology.

An Italian engineer and museum employee named Gualtiero Adami found the fossil near the village of Piné. The fossil was a small lizard-like creature with a long neck and five-digit limbs. He turned it over to the local museum, and later that year, geologist Giorgio del Piaz announced the discovery of a new genus, dubbed Tridentinosaurus antiquus. The dark-colored body outline was presumed to be the remains of carbonized skin or flesh; fossilized plant material with carbonized leaf and shoot fragments were found in the same geographical area.

The specimen wasn’t officially described scientifically until 1959 when Piero Leonardi declared it to be part of the Protorosauria group. He thought it was especially significant for understanding early reptile evolution because of the preservation of presumed soft tissue surrounding the skeletal remains. Some suggested that T. antiquus had been killed by a pyroclastic surge during a volcanic eruption, which would explain the carbonized skin since the intense heat would have burnt the outer layers almost instantly. It is also the oldest body fossil found in the Alps, at some 280 million years old.

Yet the fossil had never been carefully analyzed using modern analytical techniques, according to co-author Valentina Rossi of University College Cork in Ireland. “The fossil is unique, so this poses some challenges, in terms of analysis that we can do when effectively we cannot afford to make any mistakes, i.e., damaging the fossil,” Rossi told Ars. “Previous preliminary studies were carried out in the past but were not conclusive and the results not straightforward to interpret. The incredible technological advancement we are experiencing in paleontology made this study possible, since we can now analyze very small quantities of precious fossil material at the molecular level, without the risk of damaging the whole specimen.”

The fossil under normal light (left) and under UV light (right).

Enlarge / The fossil under normal light (left) and under UV light (right).

Valentina Rossi

Rossi et al. focused on the dark body outline believed to be carbonized soft tissue for their analysis. This involved photographing the fossil—plus some fossilized plants found in the same area—in both white light and UV light, and using those images to build a photogrammetric map and 3D model. They also took minute samples and examined them with scanning electron microscopy, micro X-ray diffraction, Raman spectroscopy, and ATF-FTIR spectroscopy.

The entire specimen, both the body outline and the bones, fluoresced yellow under UV light; the plant specimens did not. But coatings like lacquers, varnishes, glues, and some artificial pigments do fluoresce yellow under UV light. There was no evidence of fossilized melanin, which one might expect to find in preserved soft tissue. Also, fossils with preserved soft tissue are typically flattened with little topography; the T. antiquus specimen showed a lot of topographical variation in the dark outline areas.

The authors thought this was consistent with some kind of mechanical preparation, perhaps to (unsuccessfully) expose more of the skeleton. They concluded that one or more layers of some kind of coating had been applied to the body outline and the bones. The granular texture of what had been presumed to be soft tissue was more consistent with manufactured pigments used in historical paintings—specifically, “a manufactured carbon-based pigment mixed with an organic binder,” i.e., bone black paint. Conclusion: T. antiquus is a forgery and scientists therefore should be wary of using the specimen in comparative phylogenetic analysis.

Tridentinosaurus antiquus.” height=”428″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/02/fakefossil2-640×428.jpg” width=”640″>

Enlarge / Valentina Rossi with an image of Tridentinosaurus antiquus.

Zixiao Yang

How could scientists have presumed the dark outline of carbonized soft tissue for so many decades? “This fossil was discovered in 1931 and back then fossils were treated very differently than today,” said Rossi. “Application of paints, consolidates and lacquers on fossil bones was the norm, because that was the only way to protect the specimens for further deterioration. It was also sometimes to embellish specimens by making them sleek and shiny. Unfortunately, in the case of Tridentinosaurus, the mechanical preparation did most of the damage and then the application of a black paint created the illusion of a lizard-like animal impression on the surface of the rock.”

This analysis also casts doubt on the validity of the fossil’s assigned taxon, which was based on observations of the body proportion and measurements of limbs, neck, and abdomen. Part of the fossil, at least, appears to be genuine—the long bones of the hind limbs—but that doesn’t mean it will be easier now to determine species or where the specimen fits in the fossil record. “The bones that are recognizable appear to be very poorly preserved, so it might be very difficult to extrapolate any information,” said Rossi. “But perhaps the discovery of new fossil material from the same area where this specimen was found might help identify this ancient animal.”

So how can paleontologists prevent this kind of error from happening in the future? Rossi recommends reporting such finds via scientific journals with a detailed explanation of the methods that were used to characterize the surface materials on both the fossil and the rock. “It’s important to be aware that certain practices are not acceptable anymore, and not just because it creates—whether intentionally or by genuine mistake—misinformation and distorts our perception of a specimen,” said Rossi. “But also because the fossil will be irreparably damaged, and we might have lost key information about the original aspect and preservation state of the fossil.”

Paleontology, 2024. DOI: 10.1111/pala.12690  (About DOIs).

It’s a fake: Mysterious 280 million-year-old fossil is mostly just black paint Read More »

what-would-the-late-heavy-bombardment-have-done-to-the-earth’s-surface?

What would the late heavy bombardment have done to the Earth’s surface?

asteroids, craters, Earth science, geology, Impacts, planetary science, Science, tsunamis / /

Under fire —

Early in Earth’s history, bombardment by enormous asteroids was common.

–

Image of a projection of the globe, with multi-colored splotches covering its surface.

Enlarge / Each panel shows the modeled effects of early Earth’s bombardment. Circles show the regions affected by each impact, with diameters corresponding to the final size of craters for impactors smaller than 100 kilometers in diameter. For larger impactors, the circle size corresponds to size of the region buried by impact-generated melt. Color coding indicates the timing of the impacts. The smallest impactors considered in this model have a diameter of 15 kilometers.

Simone Marchi, Southwest Research Institute

When it comes to space rocks slamming into Earth, two stand out. There’s the one that killed the dinosaurs 65 million years ago (goodbye T-rex, hello mammals!) and the one that formed Earth’s Moon. The asteroid that hurtled into the Yucatan peninsula and decimated the dinosaurs was a mere 10 kilometers in diameter. The impactor that formed the Moon, on the other hand, may have been about the size of Mars. But between the gigantic lunar-forming impact and the comparatively diminutive harbinger of dinosaurian death, Earth was certainly battered by other bodies.

At the 2023 Fall Meeting of the American Geophysical Union, scientists discussed what they’ve found when it comes to just how our planet has been shaped by asteroids that impacted the early Earth, causing everything from voluminous melts that covered swaths of the surface to ancient tsunamis that tore across the globe.

Modeling melt

When the Moon-forming impactor smashed into Earth, much of the world became a sea of melted rock called a magma ocean (if it wasn’t already melted). After this point, Earth had no more major additions of mass, said Simone Marchi, a planetary scientist at the Southwest Research Institute who creates computer models of the early Solar System and its planetary bodies, including Earth. “But you still have this debris flying about,” he said. This later phase of accretion may have lacked another lunar-scale impact, but likely featured large incoming asteroids. Predictions of the size and frequency distributions of this space flotsam indicate “that there has to be a substantial number of objects larger than, say, 1,000 kilometers in diameter,” Marchi said.

Unfortunately, there’s little obvious evidence in the rock record of these impacts before about 3.5 billion years ago. So scientists like Marchi can look to the Moon to estimate the number of objects that must have collided with Earth.

Armed with the size and number of impactors, Marchi and colleagues built a model that describes, as a function of time, the volume of melt this battering must have produced at the Earth’s surface. Magma oceans were in the past, but impactors greater than 100 kilometers in diameter still melted a lot of rock and must have drastically altered the early Earth.

Unlike smaller impacts, the volume of melt generated by objects of this size isn’t localized within a crater, according to models. Any crater exists only momentarily, as the rock is too fluid to maintain any sort of structure. Marchi compares this to tossing a stone into water. “There is a moment in time in which you have a cavity in the water, but then everything collapses and fills up because it’s a fluid.”

The melt volume is much larger than the amount of excavated rock, so Marchi can calculate just how much melt might have spilled out and coated parts of the Earth’s surface with each impact. The result is an astonishing map of melt volume. During the first billion years or so of Earth’s history, nearly the entire surface would have featured a veneer of impact melt at some point. Much of that history is gone because our active planet’s atmospheric, surface, and tectonic processes constantly modify much of the rock record.

Balls of glass

Even between 3.5 and 2.5 billion years ago, the rock record is sparse. But two places, Australia and South Africa, preserve evidence of impacts in the form of spherules. These tiny glass balls form immediately after an impact that sends vaporized rock skyward. As the plume returns to Earth, small droplets begin to condense and rain down.

Spherule bed from impact S3 in drill core. Here, S3’s spherule beds were deposited in deep enough water to not be diluted by other detritus.” data-height=”2560″ data-width=”1735″ href=”https://cdn.arstechnica.net/wp-content/uploads/2024/01/Image2-IMG_1552-scaled.jpg”><span class=Spherule bed from impact S3 in drill core. Here, S3’s spherule beds were deposited in deep enough water to not be diluted by other detritus.” height=”1446″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/01/Image2-IMG_1552-980×1446.jpg” width=”980″>

Enlarge / Spherule bed from impact S3 in drill core. Here, S3’s spherule beds were deposited in deep enough water to not be diluted by other detritus.

Nadja Drabon, Harvard

“It’s remarkable that we can find these impact-generated spherule layers all the way back to 3.5 billion years ago,” said Marchi.

What would the late heavy bombardment have done to the Earth’s surface? Read More »