SEVRES, France (AP) — The kilogram is getting an update.
No, your bathroom scales won’t suddenly become kinder and a kilo of fruit will still weigh a kilo. But the way scientists define the exact mass of a kilogram is about to change.
Until now, its mass has been defined by the granddaddy of all kilos: a golf ball-sized metal cylinder locked in a vault in France. For more than a century, it has been the one true kilogram upon which all others were based.
Gathering in Versailles, west of Paris, governments are expected on Friday to approve plans to instead use a scientific formulation to define the exact mass of a kilo. The change is expected to have practical applications in industries and sciences that require ultra-precise measurements of mass.
And it will mean redundancy for the so-called Grand K, the kilo that has towered above them all since 1889.
Made of a corrosion-resistant alloy of 90 percent platinum and 10 percent iridium , the international prototype kilo has rarely seen the light of day. Yet its role has been crucial, as the foundation for the globally accepted system for measuring mass upon which things like international trade depend.
Three different keys, kept in separate locations, are required to unlock the vault where the Grand K and six official copies — collectively known as “the heir and the spares” — are entombed together under glass bell-jars at the International Bureau of Weights and Measures, in Sevres on the western outskirts of Paris.
Founded by 17 nations in 1875 and known by its French initials, the BIPM is the guardian of the seven main units humanity uses to measure its world : the meter for length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the mole for the amount of a substance and the candela for luminous intensity.
Of the seven, the kilo is the last still based on a physical artefact, the Grand K. The meter, for example, used to be a meter-long metal bar but is now defined as the length that light travels in a vacuum in 1/299,792,458th of a second.
“This, if you like, is a moment of celebration because it’s like the last standard remaining from 1875 that will finally be replaced by new innovation,” Martin Milton, the BIPM director, said in an Associated Press interview. “Everything else has been recycled and replaced and improved. This is the last improvement that dates back to the original conception in 1875. So that’s a tribute to what was done in 1875, that it’s lasted this long.”
Only exceedingly rarely, and exceedingly carefully, have the BIPM’s master kilos been gingerly taken out so that other kilos sent back to Sevres from around the world could be compared against them, to be sure they were still properly calibrated, give or take the mass of a dust particle or two.
Although many Americans commonly think of weight in pounds and ounces, the United States is officially a kilo country, too: It was one of the original 17 founders of the BIPM in 1875. The United States’ primary kilo is called K20 and was assigned to the country in 1889 by the BIPM, along with another, K4. One kilo is equivalent to 2.2 pounds.
The U.S. also has six other platinum-iridium kilos: K79, 85, 92, 102, 104 and 105. They are all looked after by the National Institute of Standards and Technology, a branch of the U.S. Commerce Department.
To verify their mass, K20 and other kilos from around three dozen other countries were measured in Sevres against the BIPM’s master kilos in a painstaking calibration exercise from 1988 to 1992. K20 was most recently then measured again at the BIPM in 2014.
Even as humans argued, fought and slaughtered each other by the tens of millions in the 20th century, they shared the kilo. The kilo allocated to China in 1983, as it started to embrace market reforms that subsequently turned it into an economic behemoth, was the first manufactured with ultra-high precision diamond machining. Allocated to Japan in 1894, K39 was later ceded to South Korea in 1958.
The kilo is “a tribute to man’s ability to collaborate,” Milton says. “It’s been called a great work of peace, actually, because it’s one of the areas where all of the states of the world come together with absolutely the same objective.”
The metal kilo is being replaced by a definition based on Planck’s constant, which is part of one of the most celebrated equations in physics but also devilishly difficult to explain . Suffice to say that the update should, in time, spare nations the need to occasionally send their kilos back to Sevres for calibration against the Grand K. Scientists instead should be able to accurately calculate an exact kilo, without having to measure one precious lump of metal against another.
Milton says the change will have applications in computing, manufacturing, pharmaceuticals, the study of climate change and other sciences where precise measurements are required.
“The system will be intrinsically correct by reference to the laws of science, the laws of nature,” he said. “We won’t have to depend on just assuming that one particular object never changes.”
Volcanic eruptions once caused mass extinctions in the oceans – could climate change do the same?
November 13, 2018
Jeremy D. Owens
Assistant Professor of Earth, Ocean and Atmospheric Science, Florida State University
Assistant Professor, College of Charleston
Jeremy D. Owens receives funding from National Science Foundation and National Aeronautics and Space Administration.
Theodore Them does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Florida State University provides funding as a member of The Conversation US.
All animals, whether they live on land or in the water, require oxygen to breathe. But today the world’s oceans are losing oxygen, due to a combination of rising temperatures and changing ocean currents. Both factors are driven by human-induced climate change.
This process has the potential to disrupt marine food chains. We already know that large hypoxic, or low-oxygen, zones can be deadly. If hypoxia expands in both size and duration, it is possible to cause widespread extinction of marine life, which has happened previously in Earth’s history.
We investigate natural, ancient changes in ocean oxygenation and the biological effects as a way of understanding the natural response to potential future climate scenarios. In a recent study, we examined links between a major volcanic event that occurred millions of years ago and changes in ocean oxygen levels. Like human activities today, this event released massive amounts of carbon dioxide and other greenhouse gases into the atmosphere.
We found that this episode appeared to trigger significant oxygen losses in the world’s ocean that lasted over one million years. Our research adds to growing evidence that marine oxygen contents are dramatically affected by warming temperatures and other climate-related feedbacks caused by the release of greenhouse gases.
Climate change is reducing the ocean’s ability to hold oxygen and increasing marine organisms’ need for it.
Are our oceans suffocating?
Scientists widely agree that human activities – mainly fossil fuel combustion, deforestation and agricultural practices – are releasing carbon dioxide and methane into the atmosphere at unprecedented rates. For the past several decades, research on climate change impacts has focused on global warming, sea level rise and ocean acidification. Now, loss of ocean oxygen is starting to receive attention.
The world’s oceans have lost more than 2 percent of their dissolved oxygen reservoir over the past five decades. In many places local factors such as nutrient pollution are making the problem worse. In U.S. waters, major hypoxic zones regularly form in the Gulf of Mexico, the Great Lakes and along the Pacific coast. Other coastal waters are similarly impacted around the world.
Hypoxia can devastate fish catches. For example, a major fish kill in the Philippines in 2002 was directly associated with declining oxygen levels in the water. A similar event occurred in Redondo Beach, California in 2011 when hypoxic conditions over several days decimated the local fish population. Ultimately, these events have significant impacts on humans, since 40 percent of the world’s population lives within roughly 60 miles of the ocean. Millions of people depend on fish for food, income or both.
Linking ancient oxygen loss to a marine mass extinction
Past volcanic eruptions are probably our only ancient analogs to modern release of greenhouse gases from human activities. To understand how these events affected the oceans, we turned to ancient marine rocks that can record the relationship between carbon dioxide releases from volcanoes, marine oxygen levels and extinction events.
One such event, which occurred 183 million years ago during the Early Jurassic, is called the Toarcian Oceanic Anoxic Event. It is renowned for major volcanism and the seventh-largest mass extinction in Earth’s history, which occurred predominantly in the oceans. The volcanism that occurred was much larger in scale than all modern volcanoes, and would have released massive amounts of greenhouse gases to the atmosphere, warming the planet dramatically.
We applied a new and novel tool – thallium isotopes – to determine the timing and amount of oxygen loss from the oceans during this event. Thallium is a soft, silvery metal that is found in various ores, including balls of manganese on the ocean floor. Isotopes are atoms of the same element that have slight mass differences because they contain varying numbers of neutrons.
Numerous minerals form in the ocean, often through reactions that involve oxygen. But the amount of free oxygen in seawater is not constant in the modern ocean, and has also varied in time. When oxygen is abundant in the ocean, manganese oxides deposit on the ocean floor, and thallium – especially its heavier isotopes – stick to them. By analyzing ancient marine sediments and looking for shifts in thallium’s isotopic value, we hypothesized that we could track the progressive loss of ocean oxygen.
Ammonite fossil from Alberta, Canada. This ammonite evolved at the end of the Toarcian Oceanic Anoxic Event and associated marine mass extinction and was used to help determine the age of the rocks. Benjamin Gill, CC BY-ND
To do this, we collected specific dark-colored sedimentary rocks from this time period at sites in Canada and Germany, which represented two different ancient oceans. We then dissolved each layer of rock to form a liquid, and isolated and purified the thallium in each sample.
We found that thallium isotopes shifted in two stages during this event. First the oceans became less oxygenated during the onset of massive volcanism, approximately 183.8 million years ago to 183.1 million years ago. Then the oceans lost even more oxygen, coinciding with the most intense phase of volcanism, which occurred from 183.1 million years ago to 182.6 million years ago.
This work shows for the first time that the global ocean lost oxygen coincidentally with the onset of volcanism. Importantly, this happened at the onset of a known extinction called the Pliensbachian-Toarcian mass extinction event. In other words, the first signs of the extinction in the fossil record coincide with oxygen loss in the oceans.
We now think that this state of low-oxygen marine conditions lasted for over one million years and across two extinction pulses. The second phase of deoxygenation was more expansive, thus causing a larger extinction. It happened even though the atmosphere contained enough oxygen to support life, much like today. Furthermore, the duration of low oxygen conditions was similar to another event that occurred 94 million years ago with biological consequences.
A global warming threshold?
The Intergovernmental Panel on Climate Change recently released a Special Report on Global Warming of 1.5°C, which called for immediate action to limit climate change to levels that will minimize environmental and ecosystem stress. Scientists broadly agree that this means preventing global average temperatures from rising more than 1.5 degrees Celsius above preindustrial levels.
The report notes that if temperatures increase by 2°C instead of 1.5°C, substantially more oxygen loss will occur in the oceans. This makes it important to continue studying ancient impacts of oxygen loss on the extinction record, so that scientists can better predict future climate scenarios. It is also important to identify areas that will be most impacted by ocean oxygen loss and limit the environmental effects that will occur as our planet continues to warm.