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Even though Kim Kardashian’s marriage didn’t last, her engagement ring will. Like forever.

February 11, 2012

I have a joke for you:

 

How long does a two million dollar engagement ring buy you with everyone’s favorite (well, mine anyways) Kardashian sister?

 

As Kris Humphries found out, about 72 days.

 

Sorry Kris, but at least you should take some comfort in the fact that the ring you gave Kim will sit as shiny as it is right now until it’s ready to win hearts and headlines once again. At least the platinum band will anyways. What I’m referring to as the simply staggering resistance of Platinum to oxidation, more commonly known as rust or tarnish.  Platinum, along with gold and to a lesser extent silver are  the only metals on the periodic table that enjoy this distinction. As a logical consequence, these metals were some of the first discovered by ancient peoples because they would have quite literally been found lying on the ground, super shiny. In fact, gold was the first metal discovered ever and goes back as far as the entire history of… well as far back as recorded history itself! I like to imagine when cavemen discovered gold they tried to eat it before proposing to cave ladies with chunks of the stuff. Given that these un-reactive metals are now relatively commonplace, the idea of a metal that doesn’t rust may not seem that cool but trust me, it is.

 

So why aren’t these magical metals applied to more commonplace items where rust is a concern? The obvious answer is their astronomical expense. Unfortunately the expense of platinum, gold and silver is not because they don’t rust but because they are super rare, representing some of the rarest elements found it the earths crust. Even if they were more common, each of these metals are extremely ductile and malleable allowing them to be easily fashioned through pulling and hammering into jewelry but preventing their use as structural metals. Gold’s softness is the origin of the quintessential gold rush miner biting into a dubious coin to ensure it’s authenticity. Thus even if you wanted to and were rich and crazy enough to do so, it would be unwise to make solid gold or platinum rims because they would buckle when popping over a curb.

 

The diamonds in Kim’s ring are another story. Formed from carbon under extreme conditions of huge temperatures and pressures, diamonds are chemically identical to pencil lead but differ in the way the atoms are arranged. Instead of being soft enough to smear onto a sheet of paper when pressed by hand, diamonds are the hardest naturally occurring substance on earth. Ironically, according to calculations using thermodynamics, a discipline used to determine the equilibrium structure for a given set of conditions and composition, diamonds should not even exist outside of the extreme conditions in which they are formed! Instead, thermodynamics predicts that diamonds should deteriorate to graphite (pencil lead) at the temperatures and pressures found around Kim Kardashian’s hand. Then why don’t they?

 

To answer that we can consider again our friends platinum and gold. It is not exactly correct to say that these metals can never oxidize, but more accurate to say that without a huge input of energy they never will. Meanwhile, metals like iron actually give off some energy when they rust. From the standpoint of iron, it is energetically favorable to rust than remain as elemental iron in the presence of oxygen. A good analogy to this kind of “favorable energetics” is a cart balanced at the top of a hill – the cart has potential energy that is converted to kinetic energy and then depleted  when it rolls down the hill. An unfavorable energy case would be a cart in a deep valley. Even though the cart could reach the top of the hill, someone would have to push it up there. Maybe you could get those cavemen to do it by feeding them gold. To transform diamonds into graphite and oxidize platinum will take energy. Lots of energy. So unless Kim visits the National Ignition Facility, an active volcano or these guys, her ring is staying put. Just maybe not on her finger.

Image: Maggie Smith / FreeDigitalPhotos.net

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Gordon Waller
About Author

Gordon is pursuing his PhD in Materials Science and Engineering and conducts research on lithium batteries. He likes cooking, textbooks, internet memes and the great outdoors. His viewpoint on science is that everything is more interesting when you understand how it works, also being able to impress (read annoy) your friends with your techno-lingo is a major perk.

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Celebrate DNA Day with a Chocolate Smoothie!

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.