The eastern inner core located beneath Indonesia's Banda Sea is growing faster than the western side beneath Brazil.
More than 5,000 kilometres beneath us, Earth's solid metal inner core wasn't discovered until 1936.
Almost a century later, we're still struggling to answer basic questions about when and how it first formed.
These aren't easy puzzles to solve. We can't directly sample the inner core, so the key to unravelling its mysteries lies in collaboration between seismologists, who indirectly sample it with seismic waves, geodynamicists, who create models of its dynamics, and mineral physicists, who study the behaviour of iron alloys at high pressures and temperatures.
Combining these disciplines, scientists have delivered an important clue about what's happening miles beneath our feet. In a new study, they reveal how Earth's inner core is growing faster on one side than the other, which could help explain how old the inner core is, and the intriguing history of Earth's magnetic field.
Earth's core was formed very early in our planet's 4.5 billion-year history, within the first 200 million years. Gravity pulled the heavier iron to the centre of the young planet, leaving the rocky, silicate minerals to make up the mantle and crust.
Earth's formation captured a lot of heat within the planet. The loss of this heat, and heating by ongoing radioactive decay, have since driven our planet's evolution. Heat loss in Earth's interior drives the vigorous flow in the liquid iron outer core, which creates Earth's magnetic field. Meanwhile, cooling within Earth's deep interior helps power plate tectonics, which shape the surface of our planet.
As Earth cooled over time, the temperature at the centre of the planet eventually dropped below the melting point of iron at extreme pressures, and the inner core started to crystallise. Today, the inner core continues to grow at roughly 1mm in radius each year, which equates to the solidification of 8,000 tonnes of molten iron every second. In billions of years, this cooling will eventually lead to the whole core becoming solid, leaving Earth without its protective magnetic field.
One might assume that this solidification creates a homogeneous solid sphere, but this isn't the case. In the 1990s, scientists realised that the speed of seismic waves travelling through the inner core varied unexpectedly. This suggested that something asymmetrical was happening in the inner core.
Specifically, the eastern and western halves of the inner core showed different seismic wavespeed variations. The eastern part of the inner core is beneath Asia, the Indian Ocean and the western Pacific Ocean, and the west lies under the Americas, the Atlantic Ocean and the eastern Pacific.
Sanne Cottaar, Author provided
The new study probed this mystery, using new seismic observations combined with geodynamic modelling and estimates of how iron alloys behave at high pressure. They found that the eastern inner core located beneath Indonesia's Banda Sea is growing faster than the western side beneath Brazil.
You can think of this uneven growth as like trying to make ice cream in a freezer that's only working on one side: ice crystals form only on the side of the ice cream where the cooling is effective. In the Earth, the uneven growth is caused by the rest of the planet sucking heat more quickly from some parts of the inner core than others.
But unlike the ice cream, the solid inner core is subject to gravitational forces which distribute the new growth evenly through a process of creeping interior flow, which maintains the inner core's spherical shape. This means that Earth is in no danger of tipping, though this uneven growth does get recorded in the seismic wavespeeds in our planet's inner core.
Dating the core
So does this approach help us understand how old the inner core might be? When the researchers matched their seismic observations with their flow models, they found that it's likely that the inner core – at the centre of the entire core which formed much earlier – is between 500 million and 1,500 million years old.
The study reports that the younger end of this age range is the better match, although the older end matches an estimate made by measuring changes in the strength of Earth's magnetic field. Whichever number turns out to be correct, it's clear that the inner core is a relative youngster, somewhere between a ninth and a third as old as Earth itself.
This new work presents a powerful new model of the inner core. However, a number of physical assumptions the authors made would have to be true for this to be correct. For example, the model only works if the inner core consists of one specific crystalline phase of iron, about which there is some uncertainty.
And does our uneven inner core make the Earth unusual? It turns out that many planetary bodies have two halves which are somehow different to each other. On Mars, the surface of the northern half is lower-lying while the southern half is more mountainous. The Moon's near-side crust is chemically different to the far-side one. On Mercury and Jupiter it's not the surface which is uneven but the magnetic field, which doesn't form a mirror image between north and south.
So while the causes for all of these asymmetries vary, Earth appears to be in good company as a slightly asymmetrical planet in a solar system of lopsided celestial bodies.
Long before Alexandria became the center of Egyptian trade, there was Thônis-Heracleion. But then it sank.
- Egypt's Thônis-Heracleion was the thriving center of Egyptian trade before Alexandria — and before earthquakes drove it under the sea.
- A rich trade and religious center, the city was at its height from the six to the fourth century BCE.
- As the city's giant temple collapsed into the Mediterranean, it pinned the newly discovered military vessel underwater.
Before Alexander the Great established Alexandria around 331 BCE, one of Egypt's primary ports on the Mediterranean Sea between the sixth and fourth centuries BCE was a place called Thônis-Heracleion.
Now researchers from the European Institute for Underwater Archaeology (IEASM), the same organization that first found the city in 2001, have announced the discovery of a couple of fascinating items from the city's heyday. Pinned beneath fallen temple stones is a surprisingly intact Egyptian military vessel from the second century BCE, and researchers have excavated a large cemetery from the fourth century BCE.
Thônis-Heracleion was one of the two primary access points to ancient Egypt from the Mediterranean. (The other, Canopus, was discovered in 1999.) For millennia, experts assumed Thônis-Heracleion were two different lost cities, but it's now known that Thônis is simply the city's Egyptian name, while Heracleion is its Greek name.
Thônis-Heracleion had been the stuff of legend before it was located, mentioned only in rare ancient texts and stone inscriptions. Herodotus seems to have been referring to Thônis-Heracleion's temple of Amun as the place where Heracles first arrived in Egypt. He also described a visit there by Helen with her lover Paris just before the outbreak of the Trojan War. In addition, 400 years later, geographer Strabo wrote that Heraclion, containing the temple of Heracles, had been located opposite Canopus across a branch of the Nile. Today we know Thônis-Heracleion's location as Egypt's Abu Qir Bay. The sunken port is about 6.5 kilometers from the coast and lies beneath ten meters of water.
Both Thônis-Heracleion and Canopus were wealthy in their day, and the temple was an important religious center. This all ended when the Egyptian dynasty created by Ptolemy set out to establish Alexandria as Egypt's center. Thônis-Heracleion and Canopus' trade — and thus wealth — was diverted to the new capital.
It was perhaps just as well, given that natural forces eventually destroyed Thônis-Heracleion. Located on the Mediterranean, the ground upon which it was built became saturated and eventually began to destabilize and liquefy. The temple of Amun probably collapsed around 140 BCE. A series of earthquakes sealed the cty's' fate around 800 CE, sending a 100 square-kilometer chunk of the Nile delta on which it was constructed under the waves. The Mediterranean's rising sea level over the next couple thousand years completed the drowning of Thônis-Heracleion.
Researchers have recovered a large collection of Thônis-Heracleion's treasures revealing an economically rich culture. Coins, bronze statuettes, and over 700 ancient ship anchors have been pulled from the waters. Divers have also identified over 70 shipwrecks. A giant statue of the Nile god Hapi took two and a half years to bring up.
An ancient vessel and a cemetery
Gold mask found in a submerged Greek cemetery.Credit: Egyptian Ministry of Tourism and Antiques
The newly discovered ship was found beneath 16 feet of hard clay, "thanks to cutting-edge prototype sub-bottom profiler electronic equipment," says Ayman Ashmawy of the Egyptian Ministry of Tourism and Antiques.
The military vessel had been moored in Thônis-Heracleion when the temple of Amun collapsed. The temple's enormous blocks fell onto the ship, sinking it. The boat is a rare find — only one other ship of its period has been found. As underwater archaeologist Franck Goddio, one of the scientists who found the city, puts it, "Finds of fast ships from this age are extremely rare."
At 80 feet long, the boat is six times as long as it is wide. Like its dually-named city, it's an amalgam of Greek and Egyptian ship-building techniques. According to expert Ehab Fahmy, head of the Central Department of Underwater Antiquities at IEASM, the boat has some classical construction features such as mortar and tenon joints. On the other hand, it was built to be rowed, and some of its wood was reused lumber, signature traits of Egyptian boat design. Its flat bottom suggests it was built for navigating the shallows of the Nile delta where the river flows into the Mediterranean.
Also found alongside the city's submerged northeastern entrance canal was a large Greek cemetery. The funerary is adorned with opulent remembrances, including a mask made of gold, shown above. A statement by the Egyptian Ministry of Tourism and Antiques describes its significance, as reported by Reuters:
"This discovery beautifully illustrates the presence of the Greek merchants who lived in that city. They built their own sanctuaries close to the huge temple of Amun. Those were destroyed simultaneously and their remains are found mixed with those of the Egyptian temple."
Excavation is ongoing, with more of Egypt's ancient history no doubt waiting beneath the waves.
The Younger Dryas impact hypothesis argues that a comet strike caused major changes to climate and human cultures on Earth about 13,000 years ago.
- A recent study overviewed the existing research on the Younger Dryas impact hypothesis.
- The study notes that there is a "synchronicity" of geochemical signals suggesting that fragments of a comet struck Earth approximately 13,000 years ago.
- Still, further research is needed to illuminate how the alleged impact might have shaped the future of human civilization.
Scientists generally agree that a massive asteroid or comet killed off the dinosaurs when it struck Earth 66 million years ago. Could a more recent cosmic impact have had the opposite effect on humans by helping usher in the dawn of civilization?
The "overwhelming consensus of the evidence" suggests that a comet did just that about 13,000 years ago, according to a new study published in Earth-Science Reviews. The study reviewed the existing research on the Younger Dryas impact hypothesis, which, in various forms, argues that a comet caused significant extinctions, climate changes, and shifts in human culture around 10,900 BCE.
The idea isn't exactly new. In his 1883 book Ragnarok: The Age of Fire and Gravel, the writer and Minnesota Congressman Ignatius L. Donnelly wrote about how a huge comet struck Earth about 12,000 years ago, destroying the mythical "lost continent" of Atlantis. But the hypothesis first entered the scientific mainstream with a 2007 study that proposed:
"...one or more large, low-density [extraterrestrial] objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering [Younger Dryas] cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America."
In other words, prehistoric humans might have witnessed a catastrophic cosmic impact that triggered widespread wildfires, global cooling, and the extinction of large animals, some of which might have preyed on humans. It's still unclear whether the impact occurred. But in the centuries after the comet allegedly struck Earth, human cultures made broad transitions away from hunter-gatherer societies toward agricultural-based civilizations.
What caused Earth's most recent cooling?
One mystery this hypothesis aims to solve is the cause of the Younger Dryas, which is the brief ice age that Earth experienced about 12,900 to 11,700 years ago. An "impact winter" might have been the culprit: it's a hypothesized scenario where a cosmic impact causes global cooling because the impact and its resulting ground fires would eject enough material into the atmosphere to significantly block radiation from the sun.
This alleged comet left no crater; proponents of the impact hypothesis argue that much of the comet likely fragmented high in the atmosphere and might have struck a large ice sheet on Earth's surface. But crater aside, the comet did seem to leave behind other evidence. One example is the Younger Dryas "black mats," which are distinctive soil layers (or "YD boundaries") that have been discovered at more than 100 sites across four continents.
A smoking gun?
It is unclear how the mats got their blackish color. One explanation is that it came from charcoal produced by wildfires. But what is clear is that the mats serve as a dividing line between epochs on Earth, mainly because only certain materials and fossils are found above or below this layer. For example, no spearheads or other archaeological evidence of the prehistoric PaleoAmerican Clovis culture has been found above the black mats.
Location map showing 53 YD boundary sites.
"More generally, many extinct megafaunal species are found below the black mat, but not within or above, including horse, camel, mastodon, direwolf, American lion," the researchers wrote.
The black mats also contain strange geochemical signals whose origins seem to fit the impact hypothesis, including:
Platinum group elements: Samples taken from ice in Greenland and boundary sites on multiple continents contain unusually high levels of platinum group elements (PGEs). Earth's crust doesn't contain many PGEs, but comets do. Volcanoes can also produce PGEs, but this process would leave behind chemical signs, which aren't found at the black mat sites. Together, this "strongly indicates an [extraterrestrial] source," the researchers wrote.
Microspherules: YD boundary sites also contain high levels of small particles called microspherules that include minerals with signs "of melting at very high temperatures," the researchers wrote. A cosmic impact can generate high temperatures, as can humans, volcanoes, and lightning. But considering the lack of evidence pointing to a terrestrial source, combined with analyses indicating that the particles mixed with extraterrestrial materials, data suggests that an impact is the most likely source.
"The only reasonable explanation for their occurrence is a major cosmic impact event," the researchers wrote. "They are found together with other high temperature melts with similar compositions at three sites. Those at Abu Hureyra, Syria, can only be explained by a cosmic impact."
Nanodiamonds: At least 22 black mat sites contain unusually high amounts of nanodiamonds, which are "extremely" rarely produced by natural terrestrial processes. "The widespread existence of all these nanodiamond forms can only be reasonably explained by a cosmic impact," the researchers wrote. Previous research has shown that the shock of a cosmic impact can generate nanodiamonds.
There is no better explanation
Opponents of the impact hypothesis could propose reasonable terrestrial explanations for some of the evidence. But proponents have synchronicity on their side: It's hard to explain how these different anomalous geochemical signals all manifested in a narrow time window, represented stratigraphically by the Younger Dryas black mats.
This synchronicity is even more compelling when you consider that we have undeniable evidence that 13,000 years ago Earth went through many species extinctions and a brief ice age. A 2008 study touched on the extinction component of the hypothesis, noting, "Stratigraphically and chronologically the extinction appears to have been catastrophic, seemingly too sudden and extensive for either human predation or climate change to have been the primary cause."
The researchers behind the recent study wrote:
"No YD [boundary] site has yet been found to be obviously inconsistent with a synchronous event circa 10,785 [BCE, plus or minus 50 years]. The only reasonable conclusion is that a major cosmic impact event occurred at this time. Its timing is so close to the onset of YD cooling that a causal link is highly likely."
Still, even if a comet caused the Younger Dryas, it remains unclear exactly how it might have affected the future of human civilization.
"Such an event might plausibly lead to human culture changes and megafaunal extinctions as proposed, but more detailed research is needed to investigate this," the researchers wrote.
The Taupo volcano was responsible for one of the most violent eruptions on record.
- The Taupo volcano is a rhyolitic supervolcano, whose caldera is filled by the largest freshwater lake in New Zealand.
- About 26,500 years ago, the Taupo volcano generated the Ōruanui eruption, one of the most violent on record.
- A recent study found that the Taupo volcano was likely responsible for increased seismic activity in nearby areas, suggesting the need for increased monitoring.
From the shores of Lake Taupo, a large freshwater lake in the center of New Zealand's North Island, visitors would have a hard time discerning the geological anomaly lurking below the surface: the Taupo volcano.
Around 26,500 years ago, the supervolcano produced one of the most powerful eruptions in geological history, spewing 750 cubic miles of ash and pumice into the air, covering far-away islands with inches of ash and forever changing the topography of the nation. The Ōruanui eruption was so strong that the volcano collapsed in on itself, forming a 360-foot-deep caldera that's now mostly filled by Lake Taupo.
The Taupo volcano has since remained active. It last erupted about 1,800 years ago, filling nearby valleys with so much ignimbrite that the valleys were leveled out. But like all volcanoes, its activity isn't limited to magmatic eruptions; it also includes earthquakes and ground deformation, which can occur without eruptions.
A study recently published in the journal Geochemistry, Geophysics, Geosystems found that the Taupo volcano underwent a period of unusually high volcanic unrest in 2019. The results don't suggest a supereruption will occur anytime soon, but it's possible that the Taupo volcano system could produce smaller eruptions in the near future, highlighting the need for improved monitoring techniques.
Taupō supervolcano and caldera – Ōruanui eruption, 25,500 years ago www.youtube.com
Volcanic unrest on North Island
It was no secret that powerful underground processes have been at work on New Zealand's North Island. After all, the region near the Taupo volcano was struck by more than 750 earthquakes in 2019 alone. But it wasn't immediately obvious that those earthquakes were caused by the sprawling volcano system; local tectonic processes unrelated to the magmatic system could have caused the quakes.
To determine the cause of the unrest, the researchers behind the new study analyzed data on the time, location, and magnitudes of recent earthquakes on North Island. The analysis showed that the likely cause of the 2019 earthquake "swarms" was an inflating magma reservoir about 3.1 miles below ground.
"This inflation was contemporaneous with the earthquake activity that was occurring at both the NE and SW edges of the broader magma reservoir," the researchers wrote. "We suggest that the reason for this seismicity distribution is that in the aseismic region below the Horomatangi Reefs the brittle-ductile transition is very shallow due to the presence of a large magma reservoir."
Will Taupo erupt soon?
Because volcanic activity can signal imminent eruptions, the researchers noted that New Zealand officials probably should have issued an alert for "minor volcanic unrest." However, they acknowledged that it would have been difficult for officials to determine the cause of the earthquakes in real time. After all, it's not easy to monitor volcanoes, especially Taupo, much of which lies under a 238-square-mile lake. It's even harder to forecast eruptions. One key reason is that volcanic unrest always precedes eruptions, but eruptions don't always follow volcanic activity.
Since the Ōruanui eruption, the Taupo volcano has erupted at least 28 times, the most powerful of which was the eruption that occurred around the year 232. What are the chances of Taupo erupting with similar force in our lifetimes? Not great. A 2020 paper published in Earth and Planetary Science Letters put the annual odds of such an eruption occurring over the next 500 years between 0.5 and 1.3 percent. Magma needs more time to accumulate before a super-eruption is likely.
Still, volcanic eruptions worldwide have killed about 2,000 people since 2000, 22 of whom died when a stratovolcano on New Zealand's White Island erupted in 2019. The researchers behind the new study said their findings highlight the need for improved monitoring techniques.
"Our findings show that Taupo needs to be carefully monitored to better understand the processes at depth and the factors that might cause similar unrest to escalate into an eruption in the future," the researchers wrote.
Scientists created the mineral lonsdaleite in a lab and tested its strength using sound waves — before it was obliterated.
This article was originally published on our sister site, Freethink.
Diamonds may be a girl's best friend because of their shine and glam, but they are also helpful in practical ways. The superstrong mineral is used as an industrial abrasive, on the edges of cutting tools, or on ultra-powerful drill bits.
Whether they are used for adornment or tools, diamonds aren't cheap. Scientists have long hoped to find a way to create a material that is as strong as diamonds. Now they may have something better.
It is believed that lonsdaleite, also called hexagonal diamond, is even stronger than diamond. But the rare six-sided crystalline mineral has seldom been found in nature — generally only at meteorite impact sites — and only in sample sizes that are too small to be measured.
Its exact hardness remained unknown — until now.
Researchers from Washington State University's Institute for Shock Physics have developed hexagonal diamonds large enough to study in a lab and test their stiffness and hardness.
"Diamond is a very unique material," Yogendra Gupta, director of the Institute for Shock Physics and an author on the study, said in a statement. "It is not only the strongest — it has beautiful optical properties and a very high thermal conductivity. Now we have made the hexagonal form of diamond, produced under shock compression experiments, that is significantly stiffer and stronger than regular gem diamonds."
Using gunpowder and compressed gas, Gupta's team launched dime-sized graphite disks at a transparent material at 15,000 miles per hour.
Upon impact, shock waves coursed through the disks, transforming them into lonsdaleite.
Measuring Strength With Sound
Sound travels more quickly via stiffer materials. So the researchers generated a small sound wave shortly after impact and used lasers to track its progress through the diamond. The lonsdaleite proved to be more stiff than diamond.
Since more rigid materials are generally harder and more resistant to scratching, they concluded that lonsdaleite is stronger than diamond — by 58%, a new record. They published their findings in Physical Review Letters.
"If someday we can produce them and polish them, I think they'd be more in-demand than cubic diamonds."
We don't need to worry that lab-created super-diamonds will make our precious jewels seem dull. The lonsdaleite only lasted a few nanoseconds before the high-velocity impact obliterated the gem — just long enough for the team to get their measurements. Gupta says if they can manage to keep them around longer, the rare, fleeting nature of the lonsdaleite could make them more valuable than cubic diamonds.
"If someday we can produce them and polish them, I think they'd be more in-demand than cubic diamonds," said Gupta. "If somebody said to you, 'look, I'm going to give you the choice of two diamonds: one is lot rarer than the other one.' Which one would you pick?"