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Fossil Trees Reveal the Oldest Known Forest in Asia

Smithsonian Magazine

Paleontologists are generally thrilled to find pieces of an ancient tree or a few well-preserved fossil leaves, but researchers in China recently hit the mother lode, uncovering an entire fossilized forest covering about 2.7 million square feet. The trees are the oldest found in Asia, providing insights into how the root systems of modern forests developed. The research appears in the journal Current Biology.

Hannah Osborne at Newsweek reports that the forest was discovered in 2016 in the Jianchuan and Yongchuan clay mines near the village of Xinhang, in the east central part of the country. The ancient trees are visible in the walls of the quarry, including the trunks and structures resembling pinecones.

The lycopsid trees date back to the Devonian period 365 million years, making them the oldest known forest discovered in Asia. But this forest was no towering cathedral of trees. Maya Wei-Haas at National Geographic reports that it’s difficult to gauge the height of the lycopsid trees because many of the tops were broken off during fossilization. But researchers estimate that, based on the size of the trunks, the trees maxed out at about 10 feet with most in the five- to six-foot range.

The ancient lycopsids didn’t look like modern trees either. Jan Zalasiewicz, a University of Leicester paleobiologist not involved in the study, writes for The Conversation that the species of tree, part of the new genus Guangdedendron, had no flowers or seeds. The short trees had trunks fringed with leaves and four short drooping branches at the top with bottle-shaped structures on their tips that spread spores. He describes the trees as “[a] little like a green, living version of an art deco streetlamp.”

A modern visitor might not recognize the lycopsid grove as a forest at all. “The large density as well as the small size of the trees could make Xinhang forest very similar to a sugarcane field, although the plants in Xinhang forest are distributed in patches,” lead author Deming Wang of Peking University says in a press release. “It might also be that the Xinhang lycopsid forest was much like the mangroves along the coast, since they occur in a similar environment and play comparable ecologic roles.”

It’s likely the forest was once part of a coastal swamp that periodically flooded. Those floods, it’s believed, buried trees in sediment, allowing them to fossilize.

The most striking part of the trees, at least for those interested in their evolution, are the roots, which are much more advanced than researchers believed they would be during the Devonian period. Wei-Haas reports that the Xinhang trees have stigmarian roots, or branching roots covered in rootlets. These same types of roots allowed trees in the swampy Carboniferous period that followed to grow much taller. Those swamps full of decaying trees eventually formed the coal seams that humans discovered hundreds of millions of years later.

“This is what fired the Industrial Revolution,” Cardiff University paleobotanist Christopher Berry, not involved in the study, tells Wei-Haas. “This is the basis of our present civilization; this little [root] structure, which we see for the first time in this forest.”

These early forests and their roots had other major impacts as well. Zalasiewicz writes that as these early forms of land vegetation proliferated, they stabilized river banks, creating new habitats where early animals including amphibians and millipedes could move onto land. And the tall, rooted trees also began sucking up and locking away so much carbon dioxide that it changed the atmosphere, plunging the world into 50 million years of glaciation.

There are so many trees in the clay pits that Wang says there’s still much more to learn about the stumpy little forest. “The continuous finding of new in-situ tree fossils is fantastic,” he says in the press release. “As an old saying goes: the best one is always the next one.”

Humans Have Bogged Down the Earth with 30 Trillion Metric Tons of Stuff, Study Finds

Smithsonian Magazine

Humans have produced a lot of stuff since the mid-20th century. From America's interstate highway system to worldwide suburbanization to our mountains of trash and debris, we have made a physical mark on the Earth that is sure to last for eons. Now a new study seeks to sum up the global totality of this prodigious human output, from skyscrapers to computers to used tissues.

That number, the researchers estimate, is around 30 trillion metric tons, or 5 million times the mass of the Great Pyramid of Giza. And you thought you owned a lot of crap.

The researchers refer to this tsunami of manmade stuff as the “technosphere.” The term "is a way of helping people recognize the magnitude and pervasive influence of humans on the planet," says Scott Wing, a paleobotanist at Smithsonian’s National Museum of Natural History and a co-author on the study published last week in the journal The Anthropocene Review. Wing is part of a group of scientists and climate leaders seeking to define a new geologic epoch reflecting the significant impact humans have had on Earth, known as the Anthropocene.

Part of defining a new epoch involves delineating its physical outlines in the Earth's layers of rock. As sediments build up over time, often with fossils and other remnants of life packed within, they provide a kind of timeline of the history of the Earth. For example, scientists were able to theorize that a large asteroid impact had wiped out the dinosaurs at the end of Cretaceous period years before finding the asteroid's crater, because they found a larger than normal amounts of iridium within sedimentary layers around the world. (Iridium is rarely found on Earth, but is much more common in comets and asteroids.)

Stratigraphers—geologists who study the strata, or layers, of the Earth—are used to thinking in time spans of millions of years, not decades. But the Anthropocene Working Group is urging the scientific community to recognize that humans are impacting the planet in unprecedented ways, and that it is time to formally recognize how significant that is. "We are now in some ways rivaling the great forces of nature in terms of the scale of our influence on the surface of the planet," Wing says.

To get a sense of that scale, members of the AWG set out to broadly estimate the mass of stuff that humanity has produced thus far. Using satellite data estimating the extent of various types of human development on the land, from cities and suburbs to railroad tracks, the researchers estimated (very roughly) that the physical technosphere comprises 30 trillion metric tons of material, and is spread over roughly 31 million square miles of Earth's surface.

In Earth’s biological ecosystems, animal and plant waste are generally reused by other organisms in an efficient cycle of life. "In the biosphere, there's no trash," Wing says. "The things that we produce become waste because there’s no part of the system that recycles those back to their original condition." Much of the material in the technosphere, by contrast, ends up in landfills where it often doesn’t decay or get reused.

This is exacerbated by the fact that humans today use up stuff very quickly. (Just think of how many new phones your friends have bought in the past few years.) "The evolution of the technosphere is exceedingly fast," says Jan Zalasiewicz, a paleobiologist at the University of Leicester in Great Britain and lead author on the new study. "Far faster than our own evolution."

Not all are convinced by the researchers’ interpretation, however. University College London climatologist Mark Maslin takes issue with the study, calling its methodology "incredibly weak." "I can pick holes in about half the numbers [in the study]," Maslin said. One example he offers is how the study uses an average density for cropland that is higher than the density of water.

Maslin and several other scientists published broader critiques of the efforts of the Anthropocene Working Group yesterday in the journal Nature. Though they agree that the Anthropocene should be considered a geologic epoch, they argue that the process of defining it as such should be much more transparent and should focus more on human impacts before 1950.

"They [the Anthropocene Working Group] instill a Eurocentric, elite and technocratic narrative of human engagement with our environment that is out of sync with contemporary thought in the social sciences and the humanities," Maslin and his colleagues wrote in their critique. "Defining a human-centered epoch will take time. It should be treated by scholars from all disciplines with the seriousness it deserves."

Wing and his co-authors acknowledge that their study's calculation is a very rough estimate. But they say that it is meant to help people think about how humans have produced nearly 100,000 times their mass in stuff to support our continued existence. "People will go 'wow,'" Wing says. "And maybe they’ll even take it a step further, and think about the trillion tons of carbon in the atmosphere that we put there."

Humans Caused a Major Shift in Earth's Ecosystems 6,000 Years Ago

Smithsonian Magazine

It’s hard to imagine a global force strong enough to change natural patterns that have persisted on Earth for more than 300 million years, but a new study shows that human beings have been doing exactly that for about 6,000 years.

The increase in human activity, perhaps tied to population growth and the spread of agriculture, seems to have upended the way plants and animals distribute themselves across the land, so that species today are far more segregated than they've been at any other time.

That’s the conclusion of a study appearing this week in the journal Nature, and the ramifications could be huge, heralding a new stage in global evolution as dramatic as the shift from single-celled microbes to complex organisms.

A team of researchers led by S. Kathleen Lyons, a paleobiologist at the Evolution of Terrestrial Ecosystems (ETE) program in the Smithsonian's National Museum of Natural History, examined the distribution of plants and animals across landscapes in the present and back through the fossil record in search of patterns.

Mostly they found randomness, but throughout time, there was always a small subset of plants and animals that showed up in relationship to one another more often than can be attributed to chance. That relationship either meant that pairs of species occur together, so when you find one, you usually find the other. Or it meant the opposite: when you find one, the other is usually not present, in which case they’re considered segregated.

An example would be that where there are cheetahs, you often find giraffes, because they prefer the same habitat. Predator-prey relationships can also cause animals to co-exist on the landscape, as in the case of dire wolves and giant ground sloths in the late Pleistocene. It’s believed that dire wolves may have preyed on baby giant ground sloths.

On the flip side, segregated animals are those that appear together less often than they would by chance alone. Today, Grevy’s zebra and colobus monkeys are rarely found together because they have evolved to exploit different landscapes. 

The surprise discovery was that for 300 million years, it was more common for species pairs to occur together—to aggregate on a landscape—than it was for them to segregate. Then the pattern flipped around 6,000 years ago in North America. Around the same time the human population was expanding and becoming dependent on agriculture, plant and animal communities shifted to a pattern dominated by segregation.

Lyons and her colleagues looked at nearly 360,000 pairs of organisms from 80 communities on different continents, but the best data available to them around the time period in question came predominantly from North America. Lyons expects the pattern shift will be evident around the globe if other researchers look for it.

“It’s striking that there’s a community structure that is changing in ways it hasn’t changed before and that appears to be associated with humans,” says Erle Ellis, a professor of geography and environmental systems at the University of Maryland and a member of the International Union of Geological Sciences Anthropocene Working Group. “I would say it’s one of the most interesting indicators I’ve ever seen of a shift in the biosphere associated with humans.”

The scientists can’t say exactly why the shift occurs at this distinct moment in human history, but they’ve gone to great lengths to rule out other possible connections, including examining ice cores to get at past climate conditions. There have been many periods of natural climate variability over those 300 million years, and still the pattern held steady, with an average of 64 percent of species pairs with significant relationships being aggregated.

After the shift 6,000 years ago, the average dropped to 37 percent. Today, a significant relationship between a pair of species is more likely to mean where you find one, you don’t find the other. In other words, species are more segregated than they’ve ever been.

Though there’s no smoking gun, Lyons has thoughts on the role humans played in this change. “We’re living in a lot of areas where species used to overlap their distributions,” she says. “They don’t overlap anymore because they can’t get through the areas where we’re living now.”

Gregory Dietl, a paleoecologist and Curator of Cenozoic Invertebrates at the Paleontological Research Institution in Ithaca, New York, says that this break in a 300-million-year-old pattern signals that we’re living in a new world, and that makes it more challenging to use the past to predict what may happen in the future.

“For me that was the big piece,” he says. “What does this more segregated pattern mean then, ultimately, for how species may adapt or just respond to climate change in the future?”

Dietl wrote a review of the study that also appears in the same issue of Nature. Like many of his colleagues who have seen the paper, he believes it’s reasonable that increased segregation may make species more vulnerable to changes in their environment.

“It probably means species are more vulnerable to extinction because there are fewer connections between them,” Lyons says. Humans have broken up plant and animal populations by destroying and fragmenting habitats. Their ranges are smaller, and no longer overlap in the way they once did.

“And because their geographic ranges are smaller, their abundances are almost certainly smaller.” But understanding how environmental changes will impact species is far more difficult in a world without clear examples from the past to rely on.

Whether more plants and animals adapt or go extinct in the future, this dramatic shift in the past highlights the extent of human influences that have prompted the official naming of a new age: the Anthropocene.

“There’s a tendency to think humans did not become a transformative force until fairly recently,” says Ellis. “But this effect can be placed at the very beginnings of agriculture. So it’s a very early indicator. The process of humans becoming distinct from other species and the way they transformed the Earth is really the cause of the Anthropocene. So this [study] is interesting in terms of asking where and when did this train leave the station?”

Watch this video in the original article

However, this study is not likely to help set the date scientists will use to mark the start of the Anthropocene. The Anthropocene Working Group is due to make that decision in 2016, and they’re more likely to rely on the accepted practice of identifying a well-defined line in the sand—or in most cases, the rock—that represents the sum of environmental changes denoting the shift from one time period to the next.

Chair of the working group and professor of paleobiology at the University of Leicester, Jan Zalasiewicz, says that line is likely to have been drawn in 1952, when fallout from thermonuclear weapons tests deposited a distinct radioactive signature in sediment around the world.

“Radionuclides do not represent as big a change to the Earth system as do the changes in population dynamics described in the paper, but they do provide a sharper time marker,” he wrote in an e-mail. And that’s what the working group is looking for. What the current paper contributes to the discussion, however, may be something even bigger on Zalasiewicz’s radar.

“This adds weight to the increasing impression that the Anthropocene is not simply different from the Holocene, but differs in some important respects also from all previous historical episodes on this planet,” he wrote. Zalasiewicz was one of the coauthors on a recent paper in The Anthropocene Review proposing that the significant impacts humans are making to life on the planet could be the start of a long transition to something completely new—a third stage in evolution.

The previous transition from single-celled organisms to complex life took roughly 100 million years, so it’s not unreasonable to suggest that we’re initiating a (very long-term) change in course for the biosphere.

Proponents of such a transition point to the global homogenization of plants and animals, the introduction of vast amounts of new energy into Earth’s system from the burning of fossil fuels, the increasing integration of technology into a global network of human interactions and the dominance of a single species, Homo sapiens, directing the evolution of other species.

If Lyons’s results can be replicated in the fossil record in other parts of the world, it would prove that our global influence on the evolution of life on Earth began thousands of years ago.

“I have to say that this result is so striking that I think it’s going to keep a lot of scientists busy trying to decipher this,” Ellis says. “They’re opening up a door to a whole new way of looking at changes in the Earth system, changes in the biosphere, changes induced by humans. This isn’t the final word, but it’s the opening salvo to a discussion on it.”

UPDATE 12/17/2015: A previous version of this article stated that elephants and giraffes form a "significant pair," when it should be giraffes and cheetahs, and that significant pairs of animals that are aggregated "always" are found together, and segregated animals are "never" seen together.

Where in the World Is the Anthropocene?

Smithsonian Magazine

Sixteen years ago, a pair of scientists introduced a new word that would shake up the geologic timeline: the Anthropocene. Also known as the "Age of Humans," the idea was first mentioned in a scientific newsletter by Nobel Prize-winning, atmospheric chemist Paul Crutzen and renowned biologist Eugene Stoermer. The duo enumerated the many impacts of human activities on the planet, outlining human induced carbon and sulfur emissions, the global run off of nitrogen fertilizers, species extinctions and destruction of coastal habitats.

Considering these vast changes, they declared the Holocene (our current 11,000-year-old geologic epoch) over. The Earth had entered a new geologic era, they said. This week, scientists are meeting to present their evidence of this new chapter of geological time to the International Geological Congress in Cape Town, South Africa.

Since it was introduced, the Anthropocene concept has resonated throughout the sciences and humanities. It's forced people to confront how, in so little time, our species has irreversibly transformed Earth’s climate, landscapes, wildlife and geology.

“Many people are using [the term] because it sums up in a word and an idea the total scale and extent of how the Earth’s system is changing because of humans,” says Jan Zalasiewicz, a University of Leicester geologist who pieces together Earth’s history using fossils.

As he watched the Anthropocene idea proliferate, he wondered whether there was some geological truth to it. Could today’s soils and sediments be distinct from those laid down in the Holocene? Are they distinct enough to name a new geologic epoch?

"The important thing is that the Earth system is changing," says Zalasiewicz. "From the point of geology, it doesn’t matter whether it’s humans causing it, or if it’s a meteorite, aliens from outer space or even my cat masterminding change to the planet." 

In 2008, he gathered a group of geologists, and together they published a list of possible geological signs of human impact in GSAToday, the magazine for the Geological Society of America. The group concluded that the Anthropocene is "geologically reasonable" and warranted further investigation.

But declaring a new geologic epoch is no small task. The official inclusion of the Anthropocene would be a major revision to the Geologic Timescale—the hulking calendar of time that divides Earth’s 4.6-billion-year history into chapters. The boundaries between each of these chapters are marked by shifts in the composition of glacial ice, tree rings, coral growth bands, seafloor and lake sediments among other layered geologic formations, found consistently throughout the world. “All of these layers contain signals within themselves, which reflect the life and the times around them, the chemical, biological and physical signals,” says Zalasiewicz. If the rocks have changed, the world must have changed, too.

Perhaps the most well known boundary is that between the Mesozoic and Cenozoic—also known as the Cretaceous-Paleogene or K/Pg boundary and formerly as the K-T boundary. Some 66 million years ago, an asteroid struck the Earth and killed off the non-avian dinosaurs. Since comets and asteroids are rich in the element iridium, and it's rare on Earth, a fine layer of iridium marks this event in the geologic record around the world. On every continent, paleontologists find fossils of large dinosaurs and certain plankton species below that stripe of iridium; above it, they find a distinct suite of plankton and no traces of non-avian dinosaur fossils. The iridium layer separates the Mesozoic, the dinosaur-filled era of life, from the Cenozoic, when mammals began taking over.

Though the iridium stripe can be found worldwide, the boundary’s official location is outside El Kef, Tunisia. There, in 2006, geologists hammered a golden spike into a hillside that displayed the telltale signs of the K/Pg boundary to serve as a reference point. Ideally, each boundary between chapters on the Geologic Timescale will have its own “golden spike” placed into an existing rock face or core (from glacial or marine sediment). Strict rules govern the boundaries and golden spikes, overseen by the International Commission on Stratigraphy within the larger International Union of Geological Sciences, lest the Geologic Timescale be swept away by fads in geology or in politics.

In 2008, the IUGS contacted Zalasiewicz with the request that he form a new committee to look into the idea of the Anthropocene. He gathered a diverse set of researchers, including geologists, climatologists, chemists, paleontologists and historians, dubbing the crew the Anthropocene Working Group (AWG). Over the past eight years, they furiously compared notes and gathered data to make their formal recommendation for the start of the Anthropocene. The group tallied up the various proposals to choose the one that best fit, publishing a summary of their work earlier this year in the journal Science

The signal that received the most attention was the radioactive fallout from nuclear tests, which left a prominent layer of plutonium in sediments and glacial ice. Even though thermonuclear weapons were not tested everywhere in the world, their evidence is global. “Once the fallout could get into the stratosphere, it was then distributed right around the planet very quickly over weeks or months,” says geologist Colin Waters of the British Geological Survey and secretary of the AWG. “Plutonium is barely present naturally; it’s very, very rare. So as soon as you start to see this increase, then you know that you’ve got 1952.” The radioactive signal disappears in 1964 after countries agreed to test nuclear devices underground.

A number of other signals also cluster around the year 1950 in what the AWG calls “The Great Acceleration,” when human population, resource use, industry and global trade took off. It’s then that many anthropogenic signals that once were local became truly global, and perhaps global enough to signify the Anthropocene. Here are some of those signals:

  • Concrete has been around since the Roman Empire, but “volumetrically most of the concrete ever produced has been since 1945 or 1950,” says Waters. That makes it a recognizable modern material. The downside? Concrete is uncommon in the oceans and absent from glacial ice so the signal isn't universal, he says.
  • Plastics were first introduced in the 1800s, but today there are more plastics around than ever before. Production expanded from 2 million tons in 1950 to 300 million tons in 2015, and it’s estimated that 40 billion tons of the stuff will exist by 2050. People like plastics because they’re lightweight and degrade slowly. But those same qualities also make plastic a good geologic indicator. Sediment samples containing plastics nearly all caome from the last half century, according to Zalasiewicz. This abundance of plastic "was almost unknown before the mid-twentieth century,” he says. On Hawaii beaches, geologists are now finding rocks they call “plastiglomerate,” which is formed when campfires melt plastics into a massive glob containing pebbles and sand. In addition, microplastics, such as tiny microbeads from cosmetics and artificial fibers from clothing, are currently forming a sedimentary layer on the seafloor. The downside of using plastics as a marker is that they are not commonly found in glacial ice, so they are not a universal signal.
  • Nearly all of the reactive nitrogen on Earth has been produced since 1913, when German chemists Fritz Haber and Carl Bosch figured out how to capture nitrogen gas from the air and turn it into fertilizer. Since then, the amount of reactive nitrogen on Earth has more than doubled, with a substantial increase around 1950 as the Green Revolution industrialized farming practices. And though it sounds like it would be a good Anthropocene marker, nitrogen doesn’t leave a strong signal in the sediments. “The processes are not quite as well understood,” says Zalasiewicz. In some remote lakes in northern Canada, far from local human influences, the dominant structures of nitrogen atoms (known as isotopes) shift around 1950, reflecting the addition of nitrogen fertilizers. But whether this shift is consistent enough across lakes throughout the world to make a good signal isn’t yet certain.
  • Burning fossil fuels releases black “fly ash” particles into the atmosphere; with no natural source, they are clear signs of human activity. Those particles are now found in lake sediments throughout the world, starting as early as 1830 in the UK, and showing a dramatic, global increase beginning around 1950. “But they peaked already around the 1970s [through the] 1990s and are starting to decline,” says Waters. So similar to radioactive nucleotides, fly ash signals a geologic shift but doesn’t make a good permanent indicator.
  • The increase in carbon emissions from burning fossil fuels is recorded in a shift in carbon isotopes, which is present in any materials that trap carbon including glacial ice, limestone, shells of marine animals (found in seafloor sediment) and corals. The signal shows up around the Industrial Revolution, with a sharp increase around 1965. It's a good signal, says Zalasiewicz, though not quite as sharp as either the fly ash or radioactivity.

Some human impacts aren’t yet visible in sediments, but could plausibly leave signals in the far future. For instance, people have extensively transformed Earth itself. We dig mines, landfills and foundations for buildings; we build dams, docks and seawalls, which alter water flow and erosion; we quarry and transport rock around the world to construct towns and cities; we churn and move topsoil for farming. Future paleontologists could find these man-made materials compressed into an unusual rock layer that would be conspicuously Anthropocene.

Then there are the future fossils left behind by today’s plants and animals—and those that will vanish as species go extinct. Any hard-bodied animal that sports a shell or is held up by bones has a chance to leave a fossil upon its death.

If we are in the midst of a mass extinction, which some scientists believe we are, the disappearance of common fossils could be another indicator. But this would be a messy signal with different changes taking place at different times around the world. “It’s a more complicated signal simply because life is more complicated than the average radionucleide or carbon isotope,” says Zalasiewicz.

Another option are the fossils from the species that dominate after extinctions, such as invasives, which might leave a cleaner signal. Zalasiewicz is currently leading a team that is studying the Pacific oyster, which was introduced from the Sea of Japan to coastlines around the world during the past century. It’s both abundant and likely to fossilize, giving it strong potential as an Anthropocene indicator.

“Where [the Pacific oysters] appear they will be a new element of the biology and therefore future paleontology in those strata,” he says. “But again because humans have transplanted different species at different times around the world, it’s a complicated or messy signal.”

These findings are all play into the AWG's presentation this week at the IGC. They originally hoped this presentation would coincide with their official submission on the Anthropocene to the International Commission on Stratigraphy. But after speaking with geologists on the commission, they decided to wait. “It’s clear that the community would be more comfortable and feel rather more grounded with a traditional golden spike type definition,” says Zalasiewicz. Collecting evidence of signals isn’t enough; they need to identify a location to hammer in the Anthropocene golden spike.

The group isn’t yet sure where they’ll place it; they’re eyeing sediment cores from the deep ocean or remote lakes where the layered signals are clear. But finding a good core comes with its own set of challenges because the layer of Anthropocene sediment is very thin. “If you went to the deep oceans, you might be talking about a millimeter or two of sediment,” says Waters. “All you need is a bivalve to crawl across the seabed and it’ll churn up the whole of the Anthropocene in one go.” In many places, trash or fishing trawls have already obliterated any potential Anthropocene layers.

The work of identifying a golden spike location will likely take years. The researchers may need to go out into the field, drill for sediment cores, and do complicated analyses to prove that the signals are consistent and global. Up to this point, AWG members have been doing this work on their own time; now they’ll need to find funding in order to devote themselves to the effort.

Zalasiewicz groans at the thought of it. “Writing grant applications is one of the world’s great soul-destroying jobs,” he says. But to stake a geologic claim to the Anthropocene and bring the world’s overseers of the geologic time scale to a vote, a bit of soul destruction may be worth it.

“The current signals that are forming are quite striking to us already, even if humans died out tomorrow,” he says, a mark will likely remain in the geologic record in the far future. “A case can be made that it can be separable as a geological time unit. We cannot go back to the Holocene.”