Ecosystem evolution in Africa

Ohio University's Nancy J. Stevens Ph.D., distinguished professor in the Department of Biomedical Sciences in the Heritage College of Osteopathic Medicine, is coauthor on a paper published in the journal Science and funded by the National Science Foundation that documents the evolution of grassland ecosystems on continental Africa.

Collaborating with an extensive team of geologists and paleoanthropologists from universities around the world, led by researchers from Baylor University and the University of Minnesota, the team synthesized data from nine Early Miocene fossil localities in the East African Rift of Kenya and Uganda to determine that the expansion of grassy biomes dominated by grasses with the C4 photosynthetic pathway in Eastern Africa occurred more than 10 million years earlier.

According to the paper, previous reconstructions of early Miocene ecosystems, 15-20 million years ago, have suggested that equatorial Africa was covered by a semi-continuous forest, with open habitats dominated by warm-season, or C4, grasses that were uncommon until 8-10 million years ago. C4 refers to the different pathways that plants use to capture carbon dioxide during photosynthesis. C4 plants produce a four-carbon molecule and are more adapted to warm or hot season condition under moist or dry environments.

As the researchers gathered expertise about geological features, isotopes and fossils found at the sites, the paradigm of a continuous forest blanketing equatorial Africa during the early Miocene shifted to a more complex mosaic of habitats that already included open environments with C4 grasses.

The result of this research pushes back the oldest evidence of C4 grass-dominated habitats in Africa -- and globally -- by more than 10 million years, with important implications for primate evolution and the origins of tropical C4 grasslands and savanna ecosystems across the African continent and around the world.

"We suspected that we would find C4 plants at some sites, but we didn't expect to find them at as many sites as we did, and in such high abundance," Daniel Peppe, lead author and associate professor at Baylor University, said.

A critical aspect of this work was that the team combined many different lines of evidence together: geology, fossil soils, isotopes and phytoliths (plant silica microfossils) to reach their conclusions.

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Isotope data strengthens suspicions of ivory stockpile theft

In January 2019, a seizure of 3.3 tons of ivory in Uganda turned up something surprising: markings on some of the tusks suggested that they may have been taken from a stockpile of ivory kept, it was thought, strictly under lock and key by the government of Burundi.

A new study from University of Utah distinguished professor Thure Cerling and colleagues, published in Proceedings of the National Academy of Sciences, uses carbon isotope science to show that the marked tusks were more than 30 years old and somehow had found their way from the guarded government stockpile into the hands of illegal ivory traders. The results suggest that governments that maintain ivory stockpiles may want to take a closer look at their inventory.

Ivory's isotope signatures

Cerling is a pioneer in the use of isotopes to answer questions about physical and biological processes. "Isotopes" of a given element refer to atoms of the element that vary in their number of neutrons, and thus vary oh-so-slightly in mass. A carbon-14 isotope has one more neutron than carbon-13, for example.

Some isotopes are stable and some are unstable. Unstable isotopes decay into other isotopes or elements through radioactive decay. Since the rate of decay is known for unstable isotopes, we can use the amounts present in a sample to determine ages. That's how carbon dating works -- it uses the rate of decay of unstable carbon-14 to determine the age of organic matter.

Around a decade ago, Cerling attended a presentation at the U by Sam Wasser of the University of Washington, who was studying the genetics of wildlife and using those tools to investigate the date and place of wildlife poaching. Cerling, recognizing that his expertise in isotope science might be able to add useful information, began an ongoing collaboration with Wasser.

In 2016, Cerling, Wasser and colleagues published a study that addressed a key question in the ivory trade: how old is the ivory seized by governments? Some traders have claimed their ivory is old, taken before 1976, and thus exempt from sales bans. And with the average size of ivory seizures more than 2.5 tons, researchers, governments and conservationists wonder how much of the ivory is recent and how much is coming from criminal stockpiles -- or is stolen from one of several ivory stockpiles held by the governments of some countries in Africa.

"Governments keep their stockpiles for multiple reasons," Wasser says. "They hope to sell the ivory for revenue, sometimes to support conservation efforts. However, they can only sell ivory from elephants that died of natural causes or were culled because they were problem animals. They can't sell seized ivory because they don't know it came from the country."

With the combination of Cerling's isotope data and Wasser's genetic data, the 2016 study found that more than 90% of seized ivory was from elephants that had been killed less than three years before. It was a sobering result, showing active and well-developed poaching and export networks. The study seemed to show that little ivory from government stockpiles had ended up on the black market.

Marked tusks

But the 2019 seizure of ivory in Uganda showed something concerning. Some of the tusks sported markings that looked suspiciously like the markings that CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, uses to inventory stockpiled ivory.

Due to the markings seen on some samples of the ivory," Cerling says, "it was thought that quite a few samples in this shipment could be related to material held in a government stockpile in Burundi. We were asked to date samples from this, and three other recent ivory seizures, to see if some samples could possibly be from older stockpiles."

To determine the ivory's age, the researchers collected small samples from the tusks and analyzed them for the amount of carbon-14 isotopes in each sample. They were looking specifically for the amount of "bomb carbon" in the tusks. Between 1945 and 1963, nuclear weapons testing doubled the amount of carbon-14 in the atmosphere, so anything living that's consumed carbon since then -- including you -- has a measurable carbon-14 signature. The amount of carbon-14 in a sample of ivory that hasn't yet radioactively decayed can tell scientists when the ivory stopped growing, or when the elephant died.

The method takes some calibration, using samples from organisms living in the same area. Some of the samples came from schoolchildren in Kenya, through a program called "Kids and Goats for Elephants." Because most families in rural Kenya keep goats the program, run by Cerling and Paula Kahumbu of WildlifeDirect engages children in collecting hair samples from goats for isotopic analysis. The isotope data is useful for many applications, including fighting elephant poaching and, in this case, calibrating the bomb carbon decay rate for more accurate dating of ivory.

A consequential result

The researchers analyzed ivory from four seizures in Angola, Hong Kong, Singapore and Uganda. Genetic data ensured that they weren't sampling two tusks from the same individual. The results of analysis from the Angola, Hong Kong and Singapore seizures were as expected -- the samples were mostly around three years after the death of the elephant, with no tusks having been taken more than 10 years previous.

But the Uganda seizure, with the inventory markings on the tusks, showed something very different. Nine of the 11 tusks tested had been taken more than 30 years before, with the dates of death ranging between 1985 and 1988. Those dates are consistent with the age of ivory in the stockpile of the government of Burundi, which was inventoried and stored in sealed containers in 1989.

"My suspicions were affirmed," Wasser says. "The bigger surprise was how near to 1989 the elephants were killed." At the time Burundi assembled its stockpile, a condition of joining CITES, which assists governments in managing ivory reserves, was that the ivory to be stockpiled was old. The results suggest that that wasn't the case, Wasser says, which would have violated conditions for Burundi to join CITES.

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Ancient helium leaking from core offers clues to Earth's formation

Helium-3, a rare isotope of helium gas, is leaking out of Earth's core, a new study reports. Because almost all helium-3 is from the Big Bang, the gas leak adds evidence that Earth formed inside a solar nebula, which has long been debated.

Helium-3 has been measured at Earth's surface in relatively small quantities. But scientists did not know how much was leaking from the Earth's core, as opposed to its middle layers, called the mantle.

The new study pins down the core as a major source of helium-3 for the Earth. Some natural processes can generate helium-3, such as the radioactive decay of tritium, but helium-3 is made primarily in solar nebulae -- massive, spinning clouds of gas and dust like the one that gave rise to our Solar System. Because helium is one of the earliest elements produced in the universe, most helium-3 can be traced back to the Big Bang.

As a planet grows, it accumulates material from its surroundings, so its composition reflects the environment in which it formed. To get high concentrations of helium-3 deep in the core, Earth would have had to form inside a thriving solar nebula, not on its fringes or during its waning phase.

The new research adds further clues to the mystery surrounding Earth's formation, lending additional evidence to the theory that our planet formed inside the solar nebula.

The study was published in the AGU journal Geochemistry, Geophysics, Geosystems, which publishes research on the chemistry, physics, geology and biology of Earth and planetary processes.

About 2,000 grams of helium-3 leak out of the Earth every year, "about enough to fill a balloon the size of your desk," said lead study author Peter Olson, a geophysicist at the University of New Mexico. "It's a wonder of nature, and a clue for the history of the Earth, that there's still a significant amount of this isotope in the interior of the Earth."

The researchers modeled helium during two key stages of Earth's history: early formation, when the planet was accumulating helium, and following the formation of the Moon, after which helium was lost. Evidence suggests an object one-third the size of the Earth hit the planet early in its history, around 4 billion years ago and that impact would have re-melted the Earth's crust, allowing much of the helium to escape. The gas continues escaping to this day.

Using the modern helium-3 leak rate along with models of helium isotope behavior, the researchers estimated there are between 10 teragrams (1013 grams) to a petagram (1015 grams) of helium-3 in the core -- a vast quantity that Olson said points to Earth's formation inside the solar nebula, where high concentrations of the gas would have allowed it to build up deep in the planet.

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Earth formed much faster than previously thought, new study shows

Illustration of protoplanetary disk

The precursor of our planet, the proto-Earth, formed within a time span of approximately five million years, shows a new study from the Centre for Star and Planet Formation (StarPlan) at the Globe Institute at the University of Copenhagen.

On an astronomical scale, this is extremely fast, the researchers explain.

If you compare the solar system's estimated 4.6 billion years of existence with a 24-hour period, the new results indicate that the proto-Earth formed in what corresponds to about a minute and a half.

Thus, the results from StarPlan break with the traditional theory that the proto-Earth formed by random collisions between larger and larger planetary bodies throughout several tens of millions of years -- equivalent to about 5-15 minutes out of the above-mentioned fictional 24 hours of formation.

Instead, the new results support a more recent, alternative theory about the formation of planets through the accretion of cosmic dust. The study's lead author, Associate Professor Martin Schiller, explains it as follows:

"The other idea is that we start from dust, essentially. Millimetre-sized objects, all coming together, raining down on the growing body and making the planet in one go," he says, adding:

"Not only is this implication of the rapid formation of the Earth interesting for our solar system. It is also interesting to assess how likely it is for planets to form somewhere else in the galaxy."

The bulk composition of the solar system

The key to the new finding came in the form of the most precise measurements of iron isotopes that have so far been published scientifically.

By studying the isotopic mixture of the metallic element in different meteorites, the researchers found only one type of meteoritic material with a composition similar to Earth: The so-called CI chondrites.

The researchers behind the study describe the dust in this fragile type of meteorite as our best equivalent to the bulk composition of the solar system itself. It was dust like this combined with gas that was funnelled via a circumstellar accretion disk onto the growing Sun.

This process lasted about five million years and our planets were made from material in this disk. Now, the researchers estimate that the proto-Earth's ferrous core also formed already during this period, removing early accreted iron from the mantle.

Two different iron compositions

Other meteorites, for example from Mars, tell us that at the beginning the iron isotopic composition of material contributing to the growing Earth was different. Most likely due to thermal processing of dust close to the young sun, the researchers from StarPlan explain.

After our solar system's first few hundred thousands of years it became cold enough for unprocessed CI dust from further out in the system to enter the accretion region of the proto-Earth.

"This added CI dust overprinted the iron composition in the Earth's mantle, which is only possible if most of the previous iron was already removed into the core. That is why the core formation must have happened early," Martin Schiller explains.

"If the Earth's formation was a random process where you just smashed bodies together, you would never be able to compare the iron composition of the Earth to only one type of meteorite. You would get a mixture of everything," he adds.

More planets, more water, perhaps more life

Based on the evidence for the theory that planets form through the accretion of cosmic dust, the researchers believe that the same process may occur elsewhere in the universe.

This means that also other planets may likely form much faster than if they grow solely from random collisions between objects in space.

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Stardust in the Antarctic snow

Antarctica illustration

The rare isotope iron-60 is created in massive stellar explosions. Only a very small amount of this isotope reaches Earth from distant stars. Now, a research team with significant involvement from the Technical University of Munich (TUM) has discovered iron-60 in Antarctic snow for the first time. The scientists suggest that the iron isotope comes from the interstellar neighborhood.

The quantity of cosmic dust that trickles down to Earth each year ranges between several thousand and ten thousand tons. Most of the tiny particles come from asteroids or comets within our solar system. However, a small percentage comes from distant stars. There are no natural terrestrial sources for the iron-60 isotope contained therein; it originates exclusively as a result of supernova explosions or through the reactions of cosmic radiation with cosmic dust.

Antarctic Snow Travels around the World

The first evidence of the occurrence of iron-60 on Earth was discovered in deep-sea deposits by a TUM research team 20 years ago. Among the scientists on the team was Dr. Gunther Korschinek, who hypothesized that traces of stellar explosions could also be found in the pure, untouched Antarctic snow. In order to verify this assumption, Dr. Sepp Kipfstuhl from the Alfred Wegener Institute collected 500 kg of snow at the Kohnen Station, a container settlement in the Antarctic, and had it transported to Munich for analysis. There, a TUM team melted the snow and separated the meltwater from the solid components, which were processed at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) using various chemical methods, so that the iron needed for the subsequent analysis was present in the milligram range, and the samples could be returned to Munich.

Korschinek and Dominik Koll from the research area Nuclear, Particle and Astrophysics at TUM found five iron-60 atoms in the samples using the accelerator laboratory in Garching near Munich. "Our analyses allowed us to rule out cosmic radiation, nuclear weapons tests or reactor accidents as sources of the iron-60," states Koll. "As there are no natural sources for this radioactive isotope on Earth, we knew that the iron-60 must have come from a supernova."

Stardust Comes from the Interstellar Neighborhood

The research team was able to make a relatively precise determination as to when the iron-60 has been deposited on Earth: The snow layer that was analyzed was not older than 20 years. Moreover, the iron isotope that was discovered did not seem to come from particularly distant stellar explosions, as the iron-60 dust would have dissipated too much throughout the universe if this had been the case. Based on the half-life of iron-60, any atoms originating from the formation of Earth would have completely decayed by now. Koll therefore assumes that the iron-60 in the Antarctic snow originates from the interstellar neighborhood, for example from an accumulation of gas clouds in which our solar system is currently located.

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