There’s still so much more for us to learn about this little blue planet. We already know the Earth has a core, but did you know that core has its own rotation? Much debated but mostly agreed, the core’s rotation is slightly different than how the rest of the planet is rotating. Scientists at USC discovered not only is this inner core rotation slowing down, but it’s also backtracking.
A 2024 study conducted at USC and published in nature used data from seismic activity to determine the changes within the core’s rotation. The research found the inner core is slowing down for the first time in approximately 40 years.
Rotating at the center of the Earth under the most severe conditions is an iron-nickel alloy that constitutes 15% of the Earth’s volume. Its size can be compared to roughly that of the moon, and it rests more than 3,000 miles below our feet. Divided into two layers—the predominantly solid inner core encased by the mostly liquid outer core—our understanding is derived primarily from seismic observations and computational modeling. According to the United States Geological Survey, the core was first discovered as recently as 1906 by British geologist R.D.Oldham and is composed “principally of iron, with about 10 percent alloy of oxygen or sulfur or nickel, or perhaps some combination of these three elements.”
The movement of this inner core has been debated by scientists for over two decades. Because we can’t actually get there, research has to be conducted from what data can be extracted from seismograms of repeating earthquakes, explosions, and volcanic eruptions. The USC scientists were able to study the seismic waves passing through the core, which allowed them to determine its progression and precise regression of rotation. Analyzing 121 repeating earthquakes from 1991 to 2023 around the South Sandwich Islands, and data from Soviet nuclear tests between 1971 and 1974, they were able to conclude this slowing process.
What does this slowing and reversing inner core mean for us on the surface?
The first thing to understand is that this directional change happens around every 70 years. Secondly, the backtracking of the inner core yields fractional differences for our experience on the surface. The change and direction of speed might cause the outer rotation to slow by a thousandth of a second. John Vidale, Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences, and co-author of the study, said, “It’s very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere.”
What’s also important to note is the effect rotation has on the electric currents of the planet. The inner movement of the Earth generates a magnetic field through a process called geodynamo. A 2025 study reported in Live Science found that the field can push oxygen levels into the surface crust, thereby affecting the habitability of the planet. Not only does this field protect us from the solar flares and winds from the sun, but it is also responsible for protecting our atmosphere and very lives.
Technology, although amazingly advanced and evolving, has limited ability to measure and study what’s happening inside our planet. This complicated collection of rotational data spanned over three decades and has seemingly produced a rather limited theory. In fact, the greatest revelation might be the proof that, as Vidale said, “The dance of the inner core might be even more lively than we know so far.”
Across Appalachia, rust-colored water seeps from abandoned coal mines, staining rocks orange and coating stream beds with metals. These acidic discharges, known as acid mine drainage, are among the region’s most persistent environmental problems. They disrupt aquatic life, corrode pipes and can contaminate drinking water for decades.
However, hidden in that orange drainage are valuable metals known as rare earth elements that are vital for many technologies the U.S. relies on, including smartphones, wind turbines and military jets. In fact, studies have found that the concentrations of rare earths in acid mine waste can be comparable to the amount in ores mined to extract rare earths.
Scientists estimate that more than 13,700 miles (22,000 kilometers) of U.S. streams, predominantly in Pennsylvania and West Virginia, are contaminated with acid mine discharge.
We and our colleagues at West Virginia University have been working on ways to turn the acid waste in those bright orange creeks into a reliable domestic source for rare earths while also cleaning the water.
Experiments show extraction can work. If states can also sort out who owns that mine waste, the environmental cost of mining might help power a clean energy future.
Rare earths face a supply chain risk
Rare earth elements are a group of 17 metals, also classified as critical minerals, that are considered vital to the nation’s economy or security.
MP Materials’ Mountain Pass Rare Earth Mine and Processing Facility, in California near the Nevada border, is one of the few rare earth mines in the U.S. Tmy350/Wikimedia Commons, CC BY-SA
China controls about 70% of global rare earth production and nearly all refining capacity. This near monopoly gives the Chinese government the power to influence prices, export policies and access to rare earth elements. China has used that power in trade disputes as recently as 2025.
The United States, which currently imports about 80% of the rare earth elements it uses, sees China’s control over these critical minerals as a risk and has made locating domestic sources a national priority.
The U.S. Geological Survey has been mapping locations for potential rare earth mining, shown in pink. But it takes years to explore a locations and then get a mine up and running. USGS
Although the U.S. Geological Survey has been mapping potential locations for extracting rare earth elements, getting from exploration to production takes years. That’s why unconventional sources, like extracting rare earth elements from acid mine waste, are drawing interest.
Turning a mine waste problem into a solution
Acid mine drainage forms when sulfide minerals, such as pyrite, are exposed to air during mining. This creates sulfuric acid, which then dissolves heavy metals such as copper, lead and mercury from surrounding rock. The metals end up in groundwater and creeks, where iron in the mix gives the water an orange color.
Expensive treatment systems can neutralize the acid, with the dissolved metals settling into an orange sludge in treatment ponds.
For decades, that sludge was treated as hazardous waste and hauled to landfills. But scientists at West Virginia University and the National Energy Technology Laboratory have found that it contains concentrations of rare earth elements comparable to those found in mined ores. These elements are also easier to extract from acid mine waste because the acidic water has already released them from the surrounding rock.
Acid mine drainage flowing into Decker’s Creek in Morgantown, West Virginia, in 2024. Helene Nguemgaing
Experiments have shown how the metals can be extracted: Researchers collected sludge, separated out rare earth elements using water-safe chemistry, and then returned the cleaner water to nearby streams.
It is like mining without digging, turning something harmful into a useful resource. If scaled up, this process could lower cleanup costs, create local jobs and strengthen America’s supply of materials needed for renewable energy and high-tech manufacturing.
But there’s a problem: Who owns the recovered minerals?
The ownership question
Traditional mining law covers minerals underground, not those extracted from water naturally running off abandoned mine sites.
Nonprofit watershed groups that treat mine waste to clean up the water often receive public funding meant solely for environmental cleanup. If these groups start selling recovered rare earth elements, they could generate revenue for more stream cleanup projects, but they might also risk violating grant terms or nonprofit rules.
To better understand the policy challenges, we surveyed mine water treatment operators across Pennsylvania and West Virginia. The majority of treatment systems were under landowner agreements in which the operators had no permanent property rights. Most operators said “ownership uncertainty” was one of the biggest barriers to investment in the recovery of rare earth elements, projects that can cost millions of dollars.
Not surprisingly, water treatment operators who owned the land where treatment was taking place were much more likely to be interested in rare earth element extraction.
Map of acid mine drainage sites in West Virginia. Created by Helene Nguemgaing, based on data from West Virginia Department of Environmental Protection, West Virginia Office of GIS Coordination, and U.S. Geological Survey
West Virginia took steps in 2022 to boost rare earth recovery, innovation and cleanup of acid mine drainage. A new law gives ownership of recovered rare earth elements to whoever extracts them. So far, the law has not been applied to large-scale projects.
Across the border, Pennsylvania’s Environmental Good Samaritan Act protects volunteers who treat mine water from liability but says nothing about ownership.
Map of acid mine drainage sites in Pennsylvania. Created by Helene Nguemgaing, based on data from Pennsylvania Spatial Data Access
This difference matters. Clear rules like West Virginia’s provide greater certainty, while the lack of guidance in Pennsylvania can leave companies and nonprofits hesitant about undertaking expensive recovery projects. Among the treatment operators we surveyed, interest in rare earth element extraction was twice as high in West Virginia than in Pennsylvania.
The economics of waste to value
Recovering rare earth elements from mine water won’t replace conventional mining. The quantities available at drainage sites are far smaller than those produced by large mines, even though the concentration can be just as high, and the technology to extract them from mine waste is still developing.
Still, the use of mine waste offers a promising way to supplement the supply of rare earth elements with a domestic source and help offset environmental costs while cleaning up polluted streams.
Early studies suggest that recovering rare earth elements using technologies being developed today could be profitable, particularly when the projects also recover additional critical materials, such as cobalt and manganese, which are used in industrial processes and batteries. Extraction methods are improving, too, making the process safer, cleaner and cheaper.
Treating acid mine drainage and extracting its valuable rare earth elements offers a way to transform pollution into prosperity. Creating policies that clarify ownership, investing in research and supporting responsible recovery could ensure that Appalachian communities benefit from this new chapter, one in which cleanup and clean energy advance together.
There was a moment in human history when our entire existence may have desperately clung to a thousand or so people. A DNA-based study found that between 800,000 and 900,000 years ago, our ancestors experienced a severe population crash.
This wasn’t humans dealing with a giant meteor like the one that wiped out the dinosaurs. It was a much slower stretch during which humanity teetered on the brink of disappearing completely. This bottleneck in the human gene pool, comprising roughly 1,280 breeding individuals, lasted about 117,000 years.
Removing representation of a human population group. Photo credit: Canva
Human population levels plummet
According to Scientific American, the study analyzed modern human genomes to piece together what the early human population looked like. By constructing a complex family tree of genes from present-day humans, researchers were able to identify important evolutionary events.
During the Early-Middle Pleistocene, a period within the Ice Age, humans faced severe weather and intense glacial cycles. Most human ancestors may have died out, clearing the path for a new human species to take their place.
Focusing on Africa, the study showed that 813,000 years ago, human populations began to recover and grow again. With an estimated two-thirds of genetic diversity potentially lost, traits like brain size appear to have been among the important features that survived. “It represents a key period of time during the evolution of humans,” population geneticist and study co-author Ziqian Hao said. “So there are many important questions to be answered.”
What we know about evolution reveals a different story than a simple, continuous line of human improvement. Over time, genetic lines disappear—not dramatically all at once. It’s a slow and steady change, generation after generation.
Human existence isn’t inevitable. Species strength or technical advancement doesn’t guarantee the future or explain our past. It’s contingent on narrow, accidental circumstances. A 2021 study showed that human evolution is better seen as a continuous flow of incremental fragments over time. Categorizing people into races and groups oversimplifies human history.
A diverse group of wooden figures. Photo credit: Canva
What does the bottleneck study say about us?
The study reveals humanity didn’t simply decline; it nearly collapsed. With over 98% of our genetic diversity erased, entire branches of the human family tree permanently ceased to exist.
It’s quite possible that if even a few more of those genetic lines had ended, human history could have vanished with them. Most branches of life don’t continue. What we witness today reflects biological persistence and countless moments that could have gone another way.
A 2024 study conducted five billion simulations, revealing that as a species’ population shrinks, its risk of extinction rises. Even stable groups can quickly collapse if their numbers suddenly drop low enough.
A 2025 study found that small populations erode genetic diversity. Isolation increases inbreeding and elevates the risk of extinction. Once a lineage shrinks, recovery becomes vastly more challenging over time. Long-term survival is an exception, not the guiding rule.
Humanity likes to think of itself as the result of an incredibly unique progression. Perhaps studies like these suggest that we are actually what remains when everything else disappears. The reason any of us live today comes down to a small group of ancient outlasters: persevering individuals whose genetic lines are the building blocks of every human living today.
Photo credit: Mickey Pullen/Smithsonian Environmental Research Center –
A long-running experiment is testing tree mixes to develop the healthiest forests.
Around the world, people plan to plant more than 1 trillion trees this decade in an ambitious effort to slow climate change and reduce biodiversity loss. But if the past is prologue, many of those planted trees won’t survive. And if they do, they could end up as biological deserts that lack the richness and resilience of healthy forests.
However, many tree-planting commitments have a critical flaw: They rely too heavily on monoculture plantations – vast areas planted with just a single tree species.
A grove of commercially grown poplar trees, planted in lines with not much active beneath them. Mint Images via Getty Images
Rather than gambling on a single species and hoping for the best, science now points to a smarter path that captures both ecological and economic benefits while minimizing risk: mixed-species plantings that mirror the biodiversity of a natural forest, ultimately creating forests that grow faster and are more resilient in the face of constant threats.
The long-running BiodiversiTREE study compares forest plots containing several tree species with single-species monocultures. The results, illustrated here, show that mixed-species plots, right, produce 80% larger trees compared with monocultures, left, resulting in denser canopy growth that creates cooler understory microclimates, leading to more abundant and species-rich communities of insects, spiders and birds. Sergio Ibarra/Smithsonian Environmental Research Center
We are community and landscape ecologists at the Smithsonian Environmental Research Center. Since 2013, we and our colleagues have been rigorously testing this idea in a large, ecosystem-scale experiment called BiodiversiTREE. The verdict is striking: Trees in mixed forests don’t just survive – they outgrow their monoculture counterparts and support dramatically more biodiversity.
Trees with diverse neighbors grow larger
Thirteen years ago, we teamed up with volunteers to plant nearly 18,000 tree seedlings on 60 acres of fallow fields on the Smithsonian Environmental Research Center campus near the Chesapeake Bay.
We didn’t plant just a single species. We planted 16 different native species from all walks of tree-life. Some species were fast-growing timber species, some were mid-story species, and some were slow-growing species that might not reach full size for a century or more.
Some plots we planted with just a single species – homogenous rows of the same species over and over again. But others were planted with random allotments of four and 12 species, reflecting the middle and upper ends of tree diversity in similar-sized areas of our local forests.
We asked a simple question: What would happen if we tried to mirror nature and plant a mixture of species instead of a monoculture?
A drone image shows some of the BiodiversiTREE plots, including monocultures, outlined in white, and mixture plantings, outlined in green. Mickey Pullen/Smithsonian Environmental Research Center
The monoculture plots – those that survived – resemble traditional plantation forestry that historically has dominated rural lands in the Southeast and Pacific Northwest in the U.S. They contain rows of tall, narrow trees with sparse canopies and little life below.
The mixed-species plots, by contrast, are layered, complex and dynamic, with foliage filling the canopy and a diversity of plants and animals thriving underneath.
These visual contrasts reflect real ecological gains. Trees grown in mixtures, including important timber species like poplar and red oak, are up to 80% larger than the same species when grown alone. Mixed plots supported fewer leaf pathogens, more abundant caterpillar communities that provide food for birds, and increased phytochemical diversity in their leaves. We hypothesize that these leaf chemicals, some of which deter animals from eating them, reduced browsing damage from hungry deer, ultimately leading to higher tree growth in the mixed plots.
Plots with several tree species also had much fuller, denser leaf canopies, leading to cooler, shadier conditions that help understory plants flourish and support up to 50% more insects, spiders and birds.
The fuller canopy of 12-species forest plots like the one above supports more insects and birds than the monoculture plots. John Parker/Smithsonian Environmental Research CenterA sycamore monoculture plot at the BiodiversiTREE project provides little canopy cover. John Parker/Smithsonian Environmental Research Center
This pattern isn’t unique to our site. The BiodiversiTREE project is part of TreeDivNet, a global network of large-scale experiments spanning more than 1.2 million trees and hundreds of species. Across continents and climates, the results are consistent: Forests with a mix of species tend to grow larger, store more carbon and better withstand stress from drought, pests and disease.
So why are monocultures still common?
Despite decades of evidence, mixed-species plantings remain relatively rare in practice. Most commercial forestry operations still rely on monocultures, and these plantations are counted toward international planting campaigns aimed at slowing climate change and reversing biodiversity loss.
Technician Shelley Bennett uses high-resolution GPS to lay out plots for an experiment at the Smithsonian Environmental Research Center in Maryland. Regan Todd/Smithsonian Environmental Research Center
A new experiment at the Smithsonian Environmental Research Center called “Functional Forests” aims to bridge some of the gaps between science and practice. We’re developing intentionally designed combinations of trees to test whether specific mixtures of species can contribute ecological benefits while also providing timber and other services that humans need to support a thriving, sustainable economy.
Each of the 20 tree species in the Functional Forests project was chosen to provide one or more benefits, including timber, wildlife habitat, food for people, resistance to deer and climate resilience. But no single species provides all of these benefits.
Some of the nearly 200 plots will contain a single species, while others include carefully selected combinations of five species assembled based on the functions they provide. Some plots are protected from deer browsing, while others are left exposed.
The Functional Forests project includes trees with edible fruits like the pawpaw (Asimina triloba), one of 20 different tree species being planted there. Jamie Pullen/Smithsonian Environmental Research Center
By comparing these approaches, we can test how different planting strategies perform across a range of goals, from timber production to food production and from biodiversity to climate resilience.
Landowners and communities have different priorities, whether that’s producing wood, supporting wildlife or creating forests that can withstand a changing climate. The idea behind Functional Forests is to design plantings that can deliver these multiple benefits all at once, rather than optimizing for just one, essentially leveraging the positive effects of biodiversity to achieve real-world goals.
Planting 1 trillion trees wisely
The stakes are high. Restoration has become a major global investment, with hundreds of billions of dollars already being spent annually. Getting it wrong means wasted resources and missed opportunities to address some of the most pressing environmental challenges of our time.
If the world is going to plant a trillion trees, we believe it needs to do more than just put seedlings in the ground. It needs to rethink what a forest should be.
The goal isn’t just to grow trees. It’s to grow forests that last.
