From The Boston Globe:
When people think of knowledge, they generally think of two sorts of facts: facts that don’t change, like the height of Mount Everest or the capital of the United States, and facts that fluctuate constantly, like the temperature or the stock market close. But in between there is a third kind: facts that change slowly. These are facts which we tend to view as fixed, but which shift over the course of a lifetime. For example: What is Earth’s population? I remember learning 6 billion, and some of you might even have learned 5 billion. Well, it turns out it’s about 6.8 billion.
Or, imagine you are considering relocating to another city. Not recognizing the slow change in the economic fortunes of various metropolitan areas, you immediately dismiss certain cities. For example, Pittsburgh, a city in the core of the historic Rust Belt of the United States, was for a long time considered to be something of a city to avoid. But recently, its economic fortunes have changed, swapping steel mills for technology, with its job growth ranked sixth in the entire United States.
These slow-changing facts are what I term “mesofacts.” Mesofacts are the facts that change neither too quickly nor too slowly, that lie in this difficult-to-comprehend middle, or meso-, scale. Often, we learn these in school when young and hold onto them, even after they change. For example, if, as a baby boomer, you learned high school chemistry in 1970, and then, as we all are apt to do, did not take care to brush up on your chemistry periodically, you would not realize that there are 12 new elements in the Periodic Table. Over a tenth of the elements have been discovered since you graduated high school! While this might not affect your daily life, it is astonishing and a bit humbling.