A bubble of gas expanding at roughly 11 million miles per hour created by the shockwave from a supernova. Credit: NASA
When stars reach the end of their lifespan, they undergo gravitational collapse at their cores. The type of explosion that results is one of the most awesome astronomical events imaginable and (on rare occasions) can even be seen with the naked eye. The last time this occurred was in 1604 when a Type Ia supernova took place over 20,000 light-years away – commonly-known as Kepler’s Supernova (aka. SN1604)
Given the massive amounts of radiation they release, past supernovae are believed to have played a role in the evolution of our planet and terrestrial life. According to new research by CU Boulder geoscientist Robert Brakenridge, these same supernovae may have left traces in our planet’s biology and geology. These findings could have implications given fears that Betelgeuse might be on the verge of going supernova.
Full length negatives of the shroud of Turin. Radiocarbon dating allowed for its true age to be determined. Credit: Wikipedia Commons
Here on Earth, Carbon is found in the atmosphere, the soil, the oceans, and in every living creature. Carbon 12 – aka. C-12, so-named because it has an atomic weight of 12 – is the most common isotope, but it is by no means the only one. Carbon 14 is another, an isotope of carbon that is produced when Nitrogen (N-14) is bombarded by cosmic radiation.
This process causes a proton to be displaced by a neutron, effectively turning atoms of Nitrogen it into an isotope of carbon – known as”radiocarbon”. It is naturally radioactive and unstable, and will therefore spontaneously decay back into N-14 over a period of time. This property makes it especially useful in a process known as “radiocarbon dating”, or carbon dating for short.
Origin of Radiocarbon:
Radiocarbon enters the biosphere through natural processes like eating and breathing. Plants and animals absorb both C-12 and C-14 in the course of their natural lifetimes simply by carrying out these basic functions. When they die, they cease to consume them, and the isotope of C-14 begins to revert back to its Nitrogen state at an exponential rate due to its radioactive decay.
Comparing the remaining C-14 of a sample to that expected from atmospheric C-14 allows the age of the sample to be estimated. In addition, scientists know that the half-life of radiocarbon is 5,730 years. This means that it takes a sample of radiocarbon 5,730 years for half of it to decay back into nitrogen.
After about 10 half-lives, the amount of radiocarbon left becomes too minuscule to measure and so this technique isn’t particularly reliable for dating specimens which died more than 60,000 years ago – i.e. during the late Middle Paleolithic (aka. Old Stone Age) period.
History of Development:
Experiments that would eventually lead to carbon dating began in the 1939s, thanks to the efforts of the Radiation Laboratory at the University of California, Berkeley. At the time, researchers were attempting to determine if any of the elements common to organic matter had isotopes with half-lives long enough to be of value in biomedical research.
By 1940, the half-life of Carbon 14 was determined, as was the mechanism through which it was created (slow neutrons interacting with Nitrogen in the atmosphere). This contradicted previous work, which held that it was the product of deuterium (H², or heavy hydrogen) and Carbon 13.
A hydrogen atom is made up of one proton and one electron, but its heavy form, called deuterium, also contains a neutron. Credit: NASA/GFSC
During World War II, Willard Libby – a chemist and graduate of Berkeley – read a paper by W. E. Danforth and S. A. Korff (published in 1939) which predicted that C 14 would be created in the atmosphere due to interactions between nitrogen and cosmic rays. From this, Libby came up with the idea of measuring the decay of C 14 as a method of dating organic material.
In 1945, Libby moved to the University of Chicago, where he began the work that would lead to the development of radiocarbon dating. In 1946, he published a paper in which he speculated that C 14 might exist within organic material alongside other carbon isotopes.
After conducting experiments, which measured C-14 in methane derived from sewage samples, Libby and his colleagues were able to demonstrate that organic matter contained radioactive C-14. This was followed by experiments involving wood samples for the tombs of two Egyptian kings, for which the age was known.
Their results proved accurate, with allowances for a small margin of error, and were published in 1949 in the journal Science. In 1960, Libby received the Nobel Prize in Chemistry for this work. Since that time, carbon dating has been used in multiple fields of science, and allowed for key transitions in prehistory to be dated.
Diagram showing how radiocarbon dating works. Credit: howstuffworks.com
Limits of Carbon Dating:
Carbon dating remains limited for a number of reasons. First, there is the assumption that the ratio of C-12 to C-14 in the atmosphere has remained constant, when in fact, the ratio can be affected by a number of factors. For instance, C-14 production rates in the atmosphere, which in turn are affected by the amount of cosmic rays penetrating the Earth’s atmosphere.
This is itself affected by things like the Earth’s magnetic field, which deflects cosmic rays. Furthermore, precise measurements taken over the last 140 years have shown a steady decay in the strength of the Earth’s magnetic field. This means there’s been a steady increase in radiocarbon production (which would increase the ratio).
Another limitation is that this technique can only be applied to organic material such as bone, flesh, or wood, and can’t be used to date rocks directly. On top of that, the addition of Carbon 12 will throw off the ration, thus leading to inaccurate assessments of a sample’s age.
This is where anthropogenic factors come into play. Since fossil fuels have no Carbon 14 content, the burning of gasoline, oil, and other hydrocarbons – and in greater and greater quantity over the course of the past century and a half – has diluted the C-14 content of the atmosphere.
On the other hand, atmospheric testing of nuclear weapons during the 1950s and 1960s is likely to have increased the Carbon 14 content of the atmosphere. In fact, research has been conducted which suggests that nuclear tests may have doubled the concentration of C-14 in this time, compared to natural production by cosmic rays.
Nevertheless, it remains the most accurate means of dating the scientific community has discovered so far. Until such time that another method becomes available – and one that produces smaller margins of error – it will remain the method of choice for archeology, paleontology, and other branches of scientific research.
Gamma ray bursts are the most energetic explosions in the Universe, outshining the rest of their entire galaxy for a moment. So, it stands to reason you wouldn’t want to be close when one of these goes off.
If comics have taught me anything, it’s that gamma powered superheroes and villains are some of the most formidable around.
Coincidentally, Gamma Ray bursts, astronomers say, are the most powerful explosions in the Universe. In a split second, a star with many times the mass of our Sun collapses into a black hole, and its outer layers are ejected away from the core. Twin beams blast out of the star. They’re so bright we can see them for billions of light-years away. In a split second, a gamma ray burst can release more energy than the Sun will emit in its entire lifetime. It’s a super-supernova.
You’re thinking “Heck, if the gamma exposure worked for Banner, surely a super-supernova will make me even more powerful than the Hulk.” That’s not exactly how this plays out.
For any world caught within the death beam from a gamma ray burst, the effects are devastating. One side of the world is blasted with lethal levels of radiation. Our ozone layer would be depleted, or completely stripped away, and any life on that world would experience an extinction level event on the scale of the asteroid that wiped out the dinosaurs.
Astronomers believe that gamma ray bursts might explain some of the mass extinctions that happened on Earth. The most devastating was probably one that occurred 450 million years ago causing the Ordovician–Silurian extinction event. Creatures that lived near the surface of the ocean were hit much harder than deep sea animals, and this evidence matches what would happen from a powerful gamma ray burst event. Considering that, are we in danger from a gamma ray burst and why didn’t we get at least one Tyrannosaurus Hulk out of the deal?
This artist’s impression of a gamma-ray burst shows the two intense beams of relativistic matter emitted by the black hole. To be visible from Earth, the beams must be pointing directly towards us. (Image: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones)
There’s no question gamma ray bursts are terrifying. In fact, astronomers predict that the lethal destruction from a gamma ray burst would stretch for thousands of light years. So if a gamma ray burst went off within about 5000-8000 light years, we’d be in a world of trouble.
Astronomers figure that gamma ray bursts happen about once every few hundred thousand years in a galaxy the size of the Milky Way. And although they can be devastating, you actually need to be pretty close to be affected. It has been calculated that every 5 million years or so, a gamma ray burst goes off close enough to affect life on Earth. In other words, there have been around 1,000 events since the Earth formed 4.6 billion years ago. So the odds of a nearby gamma ray burst aren’t zero, but they’re low enough that you really don’t have to worry about them. Unless you’re planning on living about 5 million years in some kind of gamma powered superbody.
We might have evidence of a recent gamma ray burst that struck the Earth around the year 774. Tree rings from that year contain about 20 times the level of carbon-14 than normal. One theory is that a gamma ray burst from a star located within 13,000 light-years of Earth struck the planet 1,200 years ago, generating all that carbon-14.
Clearly humanity survived without incident, but it shows that even if you’re halfway across the galaxy, a gamma ray burst can reach out and affect you. So don’t worry. The chances of a gamma ray burst hitting Earth are minimal. In fact, astronomers have observed all the nearby gamma ray burst candidates, and none seem to be close enough or oriented to point their death beams at our planet. You’ll need to worry about your exercise and diet after all.
So what do you think? What existential crisis makes you most concerned, and how do gamma ray bursts compare?
We hear that rocks are a certain age, and stars are another age. And the Universe itself is 13.7 billion years old. But how do astronomers figure this out?
I know it’s impolite to ask, but, how old are you? And how do you know? And doesn’t comparing your drivers license to your beautiful and informative “Year In Space” calendar feel somewhat arbitrary? How do we know old how everything is when what we observe was around long before calendars, or the Earth, or even the stars?
Scientists have pondered about the age of things since the beginning of science. When did that rock formation appear? When did that dinosaur die? How long has the Earth been around? When did the Moon form? What about the Universe? How long has that party been going on? Can I drink this beer yet, or will I go blind? How long can Spam remain edible past its expiration date?
As with distance, scientists have developed a range of tools to measure the age of stuff in the Universe. From rocks, to stars, to the Universe itself. Just like distance, it works like a ladder, where certain tools work for the youngest objects, and other tools take over for middle aged stuff, and other tools help to date the most ancient.
Let’s start with the things you can actually get your hands on, like plants, rocks, dinosaur bones and meteorites. Scientists use a technique known as radiometric dating. The nuclear age taught us how to blow up stuff real good, but it also helped understand how elements transform from one element to another through radioactive decay.
For example, there’s a version of carbon, called carbon-14. If you started with a kilo of it, after about 5,730 years, half of it would have turned into carbon-12. And then by 5,730 more years, you’d have about ¼ carbon-14 and ¾ carbon-12.
A list of the elements with their corresponding visible light emission spectra. Image Credit: MIT Wavelength Tables, NIST Atomic Spectrum Database, umop.net
This is known as an element’s half-life. And so, if you measure the ratio of carbon-12 to carbon-14 in a dead tree, for example, you can calculate how long ago it lived. Different elements work for different ages. Carbon-14 works for the last 50,000 years or so, while Uranium-238 has a half-life of 4.5 billion years, and will let you date the most ancient of rocks. But what about the stuff we can’t touch, like stars?
When you use a telescope to view a star, you can break up its light into different colors, like a rainbow. This is known as a star’s spectra, and if you look carefully, you can see black lines, or gaps, which correspond to certain elements. Since they can measure the ratios of different elements, astronomers can just look at a star to see how old it is. They can measure the ratio of uranium-238 to lead-206, and know how long that star has been around. How astronomers know the age of the Universe itself is one of my favorites, and we did a whole episode on this.
Artist’s conception of Planck, a space observatory operated by the European Space Agency, and the cosmic microwave background. Credit: ESA and the Planck Collaboration – D. Ducros
The short answer is, they measure the wavelength of the Cosmic Microwave Background Radiation. Since they know this used to be visible light, and has been stretched out by the expansion of the Universe, they can extrapolate back from its current wavelength to what it was at the beginning of the Universe. This tells them the age is about 13.8 billion years. Radiometric dating was a revolution for science. It finally gave us a dependable method to calculate the age of anything and everything, and finally figure out how long everything has been around.
So, fan of our videos. How old are you? Tell us in the comments below.
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