Volcanic ash might have helped the plague spread to Europe

ash: (in geology) Small, lightweight fragments of rock and glass spewed by volcanic eruptions.

bacterium: (pl. bacteria) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside of plants and animals.

Black Death: A European outbreak of bubonic plague in the Middle Ages that claimed the lives of up to 200 million people throughout a period of about four years. By the time it was over in 1351, between a quarter and half of all European residents had died.

climate: The weather conditions that typically exist in one area, in general, or over a long period.

constant: Continuous or uninterrupted.

core: Something — usually round-shaped — in the center of an object. (in geology) A long, tube-like sample removed with a drill from ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.

COVID-19: A name given to the disease that erupted into a massive global pandemic in 2020. It first emerged in 2019 and is caused by a new coronavirus known as SARS-CoV-2. Symptoms can include pneumonia, trouble breathing, feeling too tired to walk more than a few steps, fever, headaches, low blood-oxygen levels, blood clots and brain “fog.” 

city-state: A nation consisting of a single city and its surrounding countryside.

crop: (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers.

culture: (n. in social science) The typical behaviors and social practices of a related group of people (such as a tribe or nation). Their culture includes their beliefs, values and the symbols that they accept and/or use. Culture is passed on from generation to generation through learning. Scientists once thought culture to be exclusive to humans. Now they recognize some other animals show signs of culture as well, including dolphins and primates.

eclipse: This occurs when two celestial bodies line up in space so that one totally or partially obscures the other. In a solar eclipse, the sun, moon and Earth line up in that order. The moon casts its shadow on the Earth. From Earth, it looks like the moon is blocking out the sun. In a lunar eclipse, the three bodies line up in a different order — sun, Earth, moon — and the Earth casts its shadow on the moon, turning the moon a deep red.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

eruption: (in geoscience) The sudden bursting or spraying of hot material from deep inside a planet or moon and out through its surface. Volcanic eruptions on Earth usually send hot lava, hot gases or ash into the air and across surrounding land. In colder parts of the solar system, eruptions often involve liquid water spraying out through cracks in an icy crust. This happens on Enceladus, a moon of Saturn that is covered in ice.

factor: Something that plays a role in a particular condition or event; a contributor.

famine: A condition where many people go hungry because there is too little food. Droughts, flooding and other weather disasters often contribute to widespread crop failures causing famine.

geologic: An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

lunar: Of or relating to Earth’s moon.

outbreak: The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.

pandemic: An outbreak of disease that affects a large proportion of the population across much or most of the world. Among the most notable in recent decades was the years-long global COVID-19 pandemic, which was formally proclaimed by the World Health Organization on March 11, 2020.

plague: (noun) Any catastrophic event that causes destruction that can lead to sickness or death (such as a crop-destroying plague of locusts). Or any horrific infection that spreads easily and kills many people, usually quickly. Best known are the infections caused by the bacterium Yersinia pestis.

population: (in biology) A group of individuals (belonging to the same species) that lives in a given area.

rodent: A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

sea: An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body’s circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation’s railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.

trade: The buying, selling or swapping of goods or services — indeed, of anything that has value. Trade groups represent the makers or sellers of these goods and services. When nations talk about trade, they usually refer to the sale or purchasing of goods with one or more countries.

tropics: The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.

volcano: A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.

Yersinia pestis: The bacterium that causes plague, both the bubonic form (where the microbe enters the skin, often from a flea bite) and pneumonic form (that is spread by breathing in microbe-infected droplets from the air).