Tag Archives: isotope

Supernova iron isotopes are raining down on Earth

Once a massive a star runs out of hydrogen fuel, it is ready to pull the curtains — and it does so with a bang! Supernovae are the most powerful explosions in the known universe, during which the dying star expels all sorts of heavy elements previously fused by nuclear reactions. Earth and the solar system at large are regularly showered by the products of supernovae.

Now, a recent study is highlighting tangible evidence pointing to such ongoing phenomena, describing rare isotopes of iron found in deep-sea sediments that are at least 33,000 years old.

The findings were described by researchers at the Australian National University (ANU) who analyzed sediments buried deep underwater in the Indian Ocean.

Kepler’s supernova. Credit: NASA/ESA/JHU/R.Sankrit & W.Blair.

“These clouds could be remnants of previous supernova explosions, a powerful and super bright explosion of a star,” Professor Anton Wallner, a nuclear physicist at ANU, said in a statement.  

In five sediment samples, the astronomers were able to identify iron-60, a rare isotope with a half-life of 2.6 million years. Since it should completely decay within 15 million years, it’s impossible that the isotope was incorporated during Earth’s formation billions of years ago. Without a doubt, its source is extraterrestrial and supernovae seem to be the likely culprits.

Previously, iron-60 was also found in Antarctic snow and in previously dated seabed deposits, ranging from 2.6 million to 6 millions years ago.

The presence of iron-60 in the newly described sediments suggests it was deposited at a rate of around 3.5 atoms per squar centimeter per year over the past 33,000 years. This slow rate of deposition suggests that the seeding supernova must have flooded interstellar space with its isotopic products.

Although the origin of the supernova cannot be determined, the researchers believe the explosion occurred millions of years ago, and its products must still be flowing through the Local Interstellar Cloud (LIC) — the interstellar cloud in the Milky Way through which the solar system is currently moving.

In the future, the astronomers would like to refine their timeline and come to an exact idea of when these isotopes made their way to Earth and confirm whether or not the LIC is the likeliest source.

“There are recent papers that suggest iron-60 trapped in dust particles might bounce around in the interstellar medium,” Professor Wallner said. 

“So the iron-60 could originate from even older supernovae explosions, and what we measure is some kind of echo. 

“More data is required to resolve these details.” 

The findings were reported in the Proceedings of the National Academy of Sciences.

Key variable used to study Mars’ ancient atmosphere varies during the day

New research is helping to improve our understanding of how Mars lost its atmosphere — and how much of it the planet lost.

Image via Wikimedia.

A new study led by NASA shows that a key tracer used to estimate how much atmosphere the planet lost changes with the temperature and time of day on Mars. The work should help make sense of previous measurements of the tracer, which have found wildly conflicting results. Having an accurate measurement of this tracer — a particular isotope of the oxygen atom — will enable us to estimate whether Mars has ever been habitable and what it was like on its surface.

The air that was

“We know Mars had more atmosphere. We know it had flowing water. We do not have a good estimate for the conditions apart from that — how Earthlike was the Mars environment? For how long?” said Timothy Livengood of the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who led the study.

Even today, Mars has features such as dry riverbeds and mineral compounds that form in liquid water which point to much milder days in its past. One element that’s critical for such a past is a thick atmosphere that could retain enough heat for water to stay liquid on the surface.

However, Mars has lost all that atmosphere today, which transformed its climate from one that could (potentially) nurture life to the dry and freezing environment found by NASA missions such as MAVEN, Curiosity, and the Viking missions of 1976.

Naturally, researchers have a lot of questions regarding the Red Planet’s ancient atmosphere. One way to estimate its nature and properties is to look at oxygen isotopes — lighter isotopes escape into space faster than light ones, so the remaining atmosphere gets enriched in heavier ones.

In Mars’ case, the lighter (and more common) isotope of oxygen is 16O, while the heavier one is 18O. By analyzing the relative amount of each of these isotopes, researchers can get a good idea of how thick the atmosphere was on early Mars.

The glaring flaw in this approach is that the 18O/16O ratio has been measured several times, producing various readings. The new paper provides a way to resolve this discrepancy by showing that the ratio can change during the Martian day.

“Previous measurements on Mars or from Earth have obtained a variety of different values for the isotope ratio,” said Livengood. “Ours are the first measurements to use a single method in a way that shows the ratio actually varying within a single day, rather than comparisons between independent devices.”

“In our measurements, the isotope ratio varies from being about 9% depleted in heavy isotopes at noon on Mars to being about 8% enriched in heavy isotopes by about 1:30pm compared to the isotope ratios that are normal for Earth oxygen.”

This range of ratios, they explain, is consistent with previously reported measurements. This suggests that those measurements were corrent, but disagreed because the dynamics of the Martian atmosphere are more complex than we assumed.

These ratio changes throughout the day are likely a routine occurrence caused by changes in ground temperature, the team explains. Molecules with heavier isotopes likely stick to cold surface grains at night more than the lighter isotopes which are freed (thermally desorbed) as the surface warms up during the day.

As Mars’ atmosphere is mostly made up of carbon dioxide (CO2), the team studied oxygen isotopes bound up in CO2 molecules. For the observations, they used the Heterodyne Instrument for Planetary Winds and Composition developed at NASA Goddard, currently installed at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii.

“While trying to understand the broad spread in estimated isotope ratios that we retrieved from the observations, we noticed that they were correlated with the surface temperature that we also obtained,” said Livengood. “That was the insight that set us on this path.”

The paper “Evidence for diurnally varying enrichment of heavy oxygen in Mars atmosphere” has been published in the journal Icarus.

Atomium ball.

What are isotopes

Atoms are the building blocks of matter. The screen you’re reading this on, the brain you’re reading with, they’re all very organized groups of atoms. They interact in specific ways, obeying specific rules, to maintain the shape and function of objects.

None of it works, however, unless the right atoms are involved. If you try to put the wrong ones into a protein or water molecule, it breaks apart. It’s like trying to cobble together a picture using pixels of the wrong colors.

Atomium ball.

Image in Public Domain.

Given how rigorous chemistry is on this, it’s surprising to see how much variety these ‘right’ atoms can get away with. Each element on the periodic table encompasses whole families of atoms who behave the same despite some important differences — isotopes.

What are isotopes?

Isotopes are atom families that have the same number of protons, but different numbers of neutrons. The term is drawn from ancient Greek words isos and topos, meaning ‘equal place’, to signify that they belong to the same elements on the periodic table.

Atoms are made of a dense core (nucleus) orbited by a swarm of electrons. The protons and neutrons that form the core represent virtually all of an atom’s mass and are largely identical except for their electrical charges — protons carry a positive charge, while neutrons don’t have any charge. The (negatively charged) electron envelope around the core dictates how atoms behave chemically.

The kicker here is that since neutrons carry no charge, they don’t need an electron nearby to balance them out. This renders their presence meaningless in most chemical processes.

To get a bit more technical, the number of protons within an atom’s nucleus is its ‘atomic number’ (aka the ‘proton number‘, usually notated ‘Z‘). Since protons are positively charged, each atom worth its salt will try to keep the same number of electrons in orbit to balance out its overall electric charge. If not, they’ll try to find other charge-impaired atoms and form ionic compounds, like literal salt, or covalent bonds — but that’s another story for another time.

thorium-atom.

Electron shells are made of several layers/orbitals. Although depicted round here, that’s only for simplicity’s sake. These orbitals can form very complicated shapes.
Image via Pixabay.

What’s important right now is to keep in mind that these atomic numbers identify individual elements. The atomic number is roughly equivalent to an element’s numeric place in the periodic table, and in broad lines dictates how an element tends to behave. All isotopes of an element have the same atomic number. What they differ in is their ‘mass number‘ (usually abbreviated ‘A‘), which denotes the total number of protons and neutrons in an atom’s core.

In other words, isotopes are atoms of the same element — but some just weigh more.

For example, two isotopes of Uranium, U-235 and U-238, have the same atomic number (92), but mass numbers of 235 and 238, respectively. You can have two isotopes of the same mass, like C-14 and N-14, that aren’t the same element at all, with atomic numbers 6 and 7, respectively. To find out how many neutrons an isotope harbors, subtract its atomic number from its mass number.

Do isotopes actually do anything?

For the most part, no. Generally speaking, there’s little to no difference in how various isotopes of the same element behave. This is partly a function of how we decide what each element ‘is’: roughly three-quarters of naturally-occurring elements are a mixture of isotopes. The average mass of a bunch of these isotopes put together is how we determine those elements’ standard atomic weights.

But, chiefly, it comes down to the point we’ve made previously: without differences in their electron shell, isotopes simply lack the means to change their chemical behavior. Which is just peachy for us. Taken together, the 81 stable elements known to us can boast some 275 stable isotopes. There are over 800 more radioactive (unstable) isotopes out there — some natural, and some we’ve created in the lab. Imagine the headache it would cause if they all behaved in a different way. Carbon itself has 3 stable isotopes — would we even exist today if each had its own quirks?

One element whose isotopes do differ meaningfully, however, is the runt of the periodic table: hydrogen. This exception is based on the atom’s particular nature. Hydrogen is the simplest chemical element, one proton orbited by one electron. Therefore, one extra neutron in the core can significantly alter the atom’s properties.

Hydrogen Isotopes.

Hydrogen’s isotopes are important enough for industrial and scientific applications that they received their own names.
Image credits BruceBlaus / Wikimedia.

For example, two of hydrogen’s natural isotopes, H-2 and H-3, have 1 and 2 neutrons respectively. Carbon (Z=6) has 2 stable isotopes: C-12 and C-13, with 6 and 7 neutrons respectively. In relative terms, there isn’t a huge difference in the neutrons’ share in their cores: they represent 50%, and 66.6% of the atoms’ weight in H-2, H-3, and 50% and 54-ish% of the total mass in C-12 and C-13. In absolute terms, though, the difference is immense: one neutron will double the mass of a hydrogen atom — two neutrons will triple it. For comparison, a single neutron is just 16.6% of a carbon atom’s mass.

While isotopes are highly similar chemically, they do differ physically. All that weight can alter how isotopes of light elements, hydrogen especially, behave. One example of such differences is the kinetic isotope effect — basically, heavier isotopes of the same element tend to be more sluggish during chemical reactions than lighter isotopes. For heavier elements, this effect is negligible.

Another quirky property of isotopes is that they tend to behave differently when exposed to infrared range than the ‘default’ elemental atoms. So, molecules that contain isotopes will look different to the same molecule sans isotopes when seen through an infrared camera. This, agian, is caused by their extra mass — the shape and masses of atoms in a molecule change how it vibrates, which in turn, changes how they interact with photons in the infrared range.

Where do isotopes come from?

Long story short, isotopes are simply atoms with more neutrons — they were either formed that way, enriched with neutrons sometime during their life, or are originated from nuclear processes that alter atomic nuclei. So, they form like all other atoms.

Lighter isotopes likely came together a bit after the Big Bang, while heavier ones were synthesized in the cores of stars. Isotopes can also form following the interaction between cosmic rays and energetic nuclei in the top layers of the atmosphere.

CNO cycle.

The carbon-nitrogen-oxygen (CNO) cycle, one of the two known sets of fusion reactions by which stars convert hydrogen to helium. P or ‘proton’ here is a positive hydrogen ion (aka hydrogen stripped of its electron).
Image credits Antonio Ciccolella / Wikimedia.

Isotopes can also be formed from other atoms or isotopes that have undergone changes over time. One example of such a process is radioactive decay: basically, unstable isotopes tend to shift towards a stable configuration over time. This can cause one unstable isotope to change into a stable one of the same element, or into isotopes of other elements with similar nucleic structures. U-238, for example, decays into Th-234.

This process, known as beta decay, occurs when there are too many protons compared to neutrons in a nucleus (or vice-versa), so one of them transforms into the other. In the example above, the uranium atom is the parent isotope, while the thorium atom is the daughter isotope. During this process, the nucleus emits radiation in the form of an electron and an antineutrino.

What are isotopes good for?

One of the prime uses for isotopes is dating (like carbon dating). One particular trait of unstable isotopes is that they decay into stable ones — but they always do so with the exact same speed. For example, C-14’s half-life (the amount of time needed for half of all isotopes in a sample to decay) is 5,730 years.

C-14 is formed in the atmosphere, and while an organism is alive, it ingests about one C-14 atom for every trillion stable C-12 isotopes through the food it eats. This keeps the C-12 to C-14 ratio roughly stable while it is alive. Once it dies, intake of C-14 stops — so by looking at how many C-14 atoms a sample has, we can calculate how far down C-14’s half-life it’s gone, meaning we can calculate its age.

At least, in theory. All our use of fossil fuels is pumping more C-14 isotopes into the atmosphere than normal, and it’s starting to mess up the accuracy of carbon dating.

To see how many C-14 atoms something has, we use accelerator mass spectrometry — a method that separates isotopes via mass.

PET (Positron-emission tomography) scans use the decay of so-called ‘medical isotopes‘ to peer inside the body. These isotopes are produced in nuclear reactors or accelerators called cyclotrons.

Finally, we sometimes create ‘enriched’ materials, such as enriched Uranium, to be used in nuclear reactors. This process basically involves us weeding through naturally-occurring uranium atoms via various methods for heavier isotopes, then separating those. The metal that we’ve already removed the heavier isotopes from (which are more unstable and thus more radioactive than ‘regular’ uranium) is known as ‘depleted uranium’.

Earth may actually be 2 planets, new study finds

A new study that compared the chemical make-up of the Earth to that of the Moon concluded that our planet may be the result of a head-on collision between two planetary bodies: a proto-Earth and another planet called Theia.

Artistic depiction of the collision between Earth and Theia. Copyright William K. Hartmann

Artistic depiction of the collision between Earth and Theia. Copyright William K. Hartmann

The idea of a planetary collision in our planet’s early history is not new. It is generally accepted that the Moon formed as the result of a violent collision between Earth and a “planetary embryo” called Theia approximately 100 million years after the Earth formed – some 4.4 billion years ago. But the prevalent theory was that it was only a swiping collision, taking place at a small angle. UCLA researchers believe this was not the case.

A head-o collision was first proposed in 2012, by Matija Ćuk, now a research scientist with the SETI Institute, and Sarah Stewart, now a professor at UC Davis. In the same year, Robin Canup of the Southwest Research Institute reached the same conclusion. This new study analyzed rocks brought back from the Moon during the Apollo missions. Specifically, they looked at the rocks’ oxygen atoms. Oxygen makes up 90% of their volume and 50% of their weight, so there’s plenty of it to look at. Now, just like many other elements, oxygen also has some isotopes – atoms with the same structure but one or more extra neutron. For example, regular oxygen has an atomic number of 16: it has 8 protons and 8 neutrons. Let’s call it O16. But there’s also O17 and O18, that have one and two extra neutrons respectively. All the planets have a unique ratio of these isotopes, their own “isotopic fingerprint” – but the Moon and the Earth seem to have the same ratio.

“We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.

Paul Warren, Edward Young (holding a sample of a rock from the moon) and Issaku Kohl. Credits: Christelle Snow/UCLA

Paul Warren, Edward Young (holding a sample of a rock from the moon) and Issaku Kohl. Credits: Christelle Snow/UCLA

This fact is very telling. If Earth and Theia would have collided marginally, then the Earth would retain most of its initial make-up, and the Moon would have most of Theia’s make-up. A head-on collision would have mixed the two much more, up to the point where they would have a similar isotopic ratio.

“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” Young said. “This explains why we don’t see a different signature of Theia in the moon versus the Earth.”

Theia did not survive the collision, but it is believed that it now makes large parts of the Moon and even some parts of the Earth.

But not everyone agrees with this finding. A previous study from 2014 found that the isotopic ratio differs so I’d still wait for a tertiary confirmation. Both studies used precise measurements and state-of-the-art equipment.

The five newly discovered isotopes: U 218, Np 219, Bk 233, Am 223 and Am 229.

Five new isotopes discovered at Lawrence Livermore

A team at Lawrence Livermore, helped by researchers from all around the world, announced the discovery of five new isotopes, adding to the already extensive list of 3,000 isotopes of 114 confirmed chemical elements. The exotic atomic variations discovered are one isotope each of heavy elements berkelium, neptunium and uranium and two isotopes of the element americium.

The  five newly discovered isotopes: U 218, Np 219, Bk 233, Am 223 and Am 229.

The five newly discovered isotopes: U 218, Np 219, Bk 233, Am 223 and Am 229.

Atoms in a chemical element that have different numbers of neutrons than protons and electrons are called isotopes. Remember ions? Those are variations of atoms with missing or extra electrons. Isotopes are similar, only varying in neutrons – it’s still the same element. Take carbon, for instance. The most stable carbon in the Universe is C-12, which has 6 neutrons. Carbon-14 actually has 8 neutrons (2 extra), and as such it’s considered an isotope.

Now, the thing about isotopes is that they don’t last very long. C-14, for example, will eventually lose its extra neutrons and become C-12 – a process called radioactive decay. Some take longer to decay, while other isotopes transform in a flash! The experiments at the Lawrence Livermore lab are a prime example. Here, researchers shot at a 300-nanometer-thick foil of curium with accelerated calcium nuclei. When the two collided, they formed a compound system for a very short while. Using special filters composed of electrical and magnetic fields you can see what happens at the collision site down to the fraction of a second.

This is how the researchers found the isotopes of berkelium, neptunium, uranium and americium were created as the end products of such collisions. These formed a sextillionth of a second following the collision, and decayed only few milliseconds or seconds later, depending on the isotope. The findings were reported in Physics Letters B.

“These results really push what we know about nuclear structure to the extreme, neutron-deficient end of the chart of the nuclides,” Livermore researcher Dawn Shaughnessy said. “When you realize that naturally occurring uranium has 146 neutrons and this new isotope only has 124 neutrons, it shows how much more we still have yet to learn about nuclear structure and the forces that hold the nucleus together.”

It’s believed 4,000 additional, undiscovered isotopes should exist, and the Livermore researchers hope to add more new isotopes to the chart using the same technique.

New research reveals the origins of the Polish “vampires”

Middle Age Europe was a place ruled by superstition and mythical beliefs – at least some parts of it were. Now, researchers are trying to figure out what made some people in Poland believe there was an ‘outbreak of vampires’ in the 17th and 18th century.

The Vampire, by Philip Burne-Jones, 1897

Archaeologists have discovered surprisingly many burial sites of presumed vampires; people used a variety of practices to stop people from rising from the ground: from placing rocks under their chins and placing sickles across their bodies to tying them up in fetal positions and piercing them with wooden steaks. But until now, very little was known about their origin and what made people believe they were vampires.

This new study, conducted by the University of South Alabama, is the first of its kind. It suggests that unlike some historians believed, the “vampires” were not strangers – all of them were locals. The researchers studied six such graves and over a hundred regular graves, measuring the strontium isotope ratios of their permanent molars. Strontium is an element found in virtually all rocks, but with varying isotope ratios depending on the source.

Their results, which have been published open-access in PLOS ONEmakes the whole situation even more mysterious.  If the victims were locals, then what made the other folk believe they were creatures of the night? Was it something about their social behavior, or did they suffer from some sort of disease? The authors of this study propose a different theory: the alleged vampires were victims of a cholera outbreak.

“People of the post-medieval period did not understand how disease was spread, and rather than a scientific explanation for these epidemics, cholera and the deaths that results from it were explained by the supernatural – in this case, vampires,” said lead researcher Lesley Gregoricka in a press release.

We need even more studies if we want to understand what was it about these people that made others so afraid of them. I think this is the charm and challenge of modern archaeology: it’s not about discovering things as much as it is about understanding how people lived and what made them act the way they did.

Isotopes inside salmon ear tell a fishy story

According to a new study, just like tree rings carry with them hints about previous dry or rainy years, bones in fish carry with them a specific signature which records the chemical composition of the waters they used to live in.

A cross-section of a salmon otolith, also known as a fish ear stone or fish ear bone. Scientists measured Strontium ratios and identified the waters in which the fish lived for its entire life. The new fish-tracking method may help pinpoint critical habitats for fish threatened by climate change, industrial development and overfishing. Credit: Sean Brennan, University of Washington
Read more at: http://phys.org/news/2015-05-chemical-tags-ear-bones-track.html#jCp

Most vertebrates, especially fish, have what is called an ‘otolith’ – a specific bony structure inside the inner ear. The  otolith accretes layers of calcium carbonate and gelatinous matrix throughout the entire life. The accretion rate varies with growth of the fish – often less growth in winter and more in summer – which results in the appearance of rings that resemble tree rings; and just like with tree rings, scientists can figure out the age. Another interesting fact is that the otolith isn’t really digestible, so it often remains stuck in the digestive tract of fish-eating animals, and scientists can therefore reconstruct their eating habits.

But whenever the otolith grows and accretes more calcium carbonate, it also traps in other elements – extremely small fractions of the chemical makeup of the waters in which the fish live in. Specifically, it traps in specific isotopes, in specific quantities; by analyzing these isotopes, researchers are now able to reconstruct where the fish was born and where it traveled for its entire life.

Sean Brennan from the University of Washington and lead author explains:

“Each fish has this little recorder, and we can reveal the whole life history of the fish from the perspective of the otolith. Each growth ring is a direct reflection of the environment the fish was swimming in at the time it was formed.” Brennan completed the study as a doctoral student at the University of Alaska Fairbanks. He is now a postdoctoral researcher in the University of Washington’s School of Aquatic and Fishery Sciences.

Specifically, they looked at the trace element strontium. Strontium is a very reliable element for this type of reconstructions because it almost never alters and strontium levels vary greatly depending on the age and structure of the bedrock. In other words, by looking at how the strontium in an area looks like you can figure out (to some extent) where it comes from. But it wasn’t an easy feat. Thure Cerling, also an author, explains:

“There are literally thousands of measurements on each otolith,” Cerling says.

Geochemist Diego Fernandez further adds:

“They’re like microexplosions. You create tiny, tiny particles that are carried into the mass spectrometer.” By showing how the ratio of strontium-87 to strontium-86 changed over time, “we get the entire life history of the salmon,” he says.

Some areas more than others are better candidates for this type of analysis, but researchers wanted a challenge – so they chose Alaska.

“Alaska is a mosaic of geologic heterogeneity,” he added. “As long as you can look at a geologic map and see rocks that are really different, that’s a good potential area.”

One of the many tributaries to the Upper Nushagak River. Credit: Sean Brennan, U of Washington

About 200,000 Chinook salmons make their way to the breeding grounds in Bristol Bay every year. When the eggs hatch in the spring, the little salmons spend a whole year in the river before venturing to the Bering Sea, and ultimately, the Pacific Ocean.

This is not only an extremely exciting find, but one that can have a great effect on fish populations throughout the world. By analyzing several otoliths, scientists can now see if their migratory patterns have remained similar, or if they have changed – likely due to some stress. From a conservation standpoint, that’s a game changer.

“This is science responding to a societal issue and need,” said co-author Christian Zimmerman, U.S. Geological Survey ecologist and chief of water and interdisciplinary studies at the USGS Alaska Science Center in Anchorage. “Using this approach, we will be able to map salmon productivity and determine how freshwater habitats influence the ultimate number of salmon. With declines in Chinook salmon in Western Alaska, fishery and land-use managers need better information about freshwater habitats to guide conservation.”

But it’s not just fish – the same technique could be used for other animals. Strontium is known to accumulate in bird feathers and teeth and also survives even after being fossilized. It could help us understand moving patterns better than ever.

Journal Reference: Sean R. Brennan, Christian E. Zimmerman, Diego P. Fernandez, Thure E. Cerling, Megan V. McPhee, Matthew J. Wooller. Strontium isotopes delineate fine-scale natal origins and migration histories of Pacific salmon. DOI: 10.1126/sciadv.1400124

earth_impact_moon

There’s an ancient Earth within a new Earth, new geochemistry findings suggest

Billions of years ago, our ancient planet collided with a Mars-sized object called Theia. The impact released tremendous amounts of energy which is thought to have produced a whole mantle magma ocean, which should have erased pre-existing chemical heterogeneities within the Earth. Following the onslaught, a new Earth formed, along with the moon. New geochemical findings hint that the impact didn’t completely melt the whole planet, leaving clumps and patches intact. This ancient past is thought to still ripple in Earth’s mantle.

Earthception

earth_impact_moon

Image: Mr Edens

According to lead researcher Associate Professor Sujoy Mukhopadhyay (Harvard): “The energy released by the impact between the Earth and Theia would have been huge, certainly enough to melt the whole planet. But we believe that the impact energy was not evenly distributed throughout the ancient Earth. This means that a major part of the impacted hemisphere would probably have been completely vaporised, but the opposite hemisphere would have been partly shielded, and would not have undergone complete melting”.

The researchers analyzed the ratios of noble isotopes harvested from deep within the Earth’s mantle, then compared them with those collected nearer to the surface. The found that 3He to 22Ne ratio from the shallow mantle is significantly higher than the equivalent ratio in the deep mantle. Analysis of the 129-Xenon to 130-Xenon ratio came out similarly. If the 4.5 billion year-old Theia impact had completely melted ancient Earth, then we should have seen a more evenly mixed mantle.

Professor Mukhopadhyay continued: “The geochemistry indicates that there are differences between the noble gas isotope ratios in different parts of the Earth, and these need to be explained. The idea that a very disruptive collision of the Earth with another planet-sized body, the biggest event in Earth’s geological history, did not completely melt and homogenize the Earth challenges some of our notions on planet formation and the energetics of giant impacts. If the theory is proven correct, then we may be seeing echoes of the ancient Earth, from a time before the collision”.
Commenting, Professor Richard Carlson (Carnegie Institute of Washington), Past President of the Geochemical Society said: “This exciting result is adding to the observational evidence that important aspects of Earth’s composition were established during the violent birth of the planet and is providing a new look at the physical processes by which this can occur”.

The findings were presented at the at the Goldschmidt conference in Sacramento, California.

: Heat map showing the production of exotic isotopes at the RIKEN Radioactive Isotope Beam Factory (RIBF). This facility can produce nickel-78 (78Ni) in yields sufficient for highly precise decay measurements. Credit: The American Physical Society

Nickel-78: a ‘doubly magic’ isotope

Some atoms are more stable than others, and the same goes for their isotopes – elements that have the same number of protons in the nucleus, but different number of neutrons. For instance, some decay in a trillionth of a second, while others can live on for billions of years. Actually, using isotopes (thorium and uranium decay) scientists were able to refine the dating for our planet’s age. The Earth is 4.54 billion years old.

The most exceptional isotopes are those that contain a ‘magic number’, as defined by scientists.The seven most widely recognized magic numbers are 2, 8, 20, 28, 50, 82 and 126, corresponding to the total number of protons and neutrons needed to completely fill the nuclear shells. Nickel-78 is perhaps the oddest of isotopes, and has been giving physicists headaches for ages because it is a ‘doubly magic’ isotope.

The nickel-78 (78-Ni) isotope contains 28 protons and 50 neutrons, making it doubly magic according to this series, but isotopes that exhibit such an excess of neutrons over protons are predicted to have a different magic number, according to models. This has prompted some scientists to say Nickel-78 isn’t magic at all.

: Heat map showing the production of exotic isotopes at the RIKEN Radioactive Isotope Beam Factory (RIBF). This facility can produce nickel-78 (78Ni) in yields sufficient for highly precise decay measurements. Credit: The American Physical Society

: Heat map showing the production of exotic isotopes at the RIKEN Radioactive Isotope Beam Factory (RIBF). This facility can produce nickel-78 (78Ni) in yields sufficient for highly precise decay measurements. Credit: The American Physical Society

Helping put an end to the debate are Shunji Nishimura and colleagues from the RIKEN Nishina Center for Accelerator-Based Science who have performed extensive experiments on Nickel-78.

“Many experiments have been carried out to identify systematic trends in nuclear properties near 78Ni,” says Nishimura. “Yet there has been no clear evidence on whether 78Ni is a double-magic nuclei due to the extremely low production yield of this isotope.”

The team used RIKEN’s Radioactive Isotope Beam Factory, which is capable of generating high yields of exotic and rare isotopes like 78Ni, as show in the figure above. Using this facility, in combination with the newly developed WAS3ABi detector, the research team was able to perform measurements of 78Ni decay with unprecedented precision. The experiments confirmed the doubly magic status of 78Ni, providing valuable insights into the behavior of exotic nuclei with large neutron excess. Such neutron-rich nuclei play an important role in the production of elements heavier than the most stable element iron, such as gold and uranium.

“We hope to solve one of the biggest mysteries of this century—where and how were the  created in the Universe?” explains Nishimura.

Findings were detailed in a paper published in the journal Physical Review Letters.

52.000 year old forest discovered underwater [stunning pictures and video]

Scuba divers have discovered a primeval underwater forest off the coast of Alabama – a cypress forest which was incredibly well preserved for over 50.000 years.

underwater forest1

The bald cypress forest was buried under ocean sediments (almost certainly sand), isolated from oxygen (which is the main enemy of preservation), thus preventing them from rotting; however, the underwater forest was uncovered by hurricane Katrina, in 2005, explains Ben Raines, one of the first divers to explore it.

“Swimming around amidst these stumps and logs, you just feel like you’re in this fairy world,” Raines said.

The trees are so well preserved that when cut, they still smell like fresh cypress! The remaining stumps of the small forest cover an area of over 1.3 km, and lie about 18 meters below the surface of the Gulf of Mexico. The bad news is that even though it was recently discovered, now that it is subject to the action of oxygen and marine animals, it will only take another few years before it is destroyed. Even as little as two years could destroy it.

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“The longer this wood sits on the bottom of the ocean, the more marine organisms burrow into the wood, which can create hurdles when we are trying to get radiocarbon dates,” Harley said. “It can really make the sample undatable, unusable.”

The forest was dated with the help of carbon isotopes, but the trees’ rings can offer valuable information about the climate of the Gulf of Mexico thousands of years ago, during a period known as the Wisconsin Glacial period, when sea levels (and temperatures) were much lower than they are today.

 

“These stumps are so big, they’re upwards of two meters in diameter — the size of trucks,” Harley explained. “They probably contain thousands of growth rings.”