Science word of the day: Covalent

Pronunciation: Coh-VAY'-lent

What it means: In chemistry, a covalent bond occurs when two atoms share a pair of electrons. Electrons zip around atomic nuclei at different energy levels, or "shells." An atom fills its shells with electrons starting from the lowest-energy shell to the highest-energy one, which is called the valence shell. Valence-shell electrons can interact with the valence shells of other atoms. When two atoms get close enough, their valence electrons can feel the pull from both nuclei at once, binding the two atoms together into a stable molecule.

How to use it in a sentence: When atoms share electrons in a covalent bond, they form some of the most stable bonds in chemistry ‪—‬ which is good news, because these bonds are also the basis of most organic molecules and organisms, including you.

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Science word of the day: Coprolite

Pronunciation: KAHP'-ruh-lite

What it means: Coprolites are fossilized poop. Scientists have found coprolites from animals as diverse as fish, dinosaurs and saber-toothed cats. Teeth in the saber-toothed cat poop indicated that it had been eating baby sloths, which frankly feels a bit unfair from a creature with 11-inch-long (28 centimeters) teeth.

These fossils form when poop gets rapidly buried and mineralized instead of rotting away. Coprolites can be hard to match to the animal that produced them, but undigested bones and teeth in the fossilized poop can often provide clues to the kinds of animals that other animals eat.

How to use it in a sentence: If you're ever in a science museum and a volunteer, with a twinkle in their eye, asks you what you think a chunky, rock-looking thing is, the answer is always coprolite.

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Science word of the day: Allele

Pronunciation: Ah-LEEL'

What it means: Genes contain the instructions for the various proteins that determine traits, such as eye color or blood type. An allele is a specific variant of a gene. Alleles come in pairs, one from each parent. Some are dominant, meaning that copy will override any instruction from the other allele in the pair, and some are recessive, meaning there have to be two copies of that particular allele for those instructions to translate into an observable feature. Of course, not all inheritance is as simple as dominant and recessive patterns, particularly for traits that arise from combinations of hundreds of genes.

How to use it in a sentence: We learned in grade school that alleles for brown eyes are dominant over alleles for blue eyes, leaving the kids with hazel eyes feeling lost and confused.

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Science word of the day: Seamount

Pronunciation: SEE'-mount

What it means: A seamount is an undersea mountain that rises at least 3,300 feet (1,000 meters) above the seafloor but does not come close to breaking the surface. According to the National Oceanic and Atmospheric Administration, there are at least 100,000 seamounts in the oceans, and less than 0.1% of them have been explored. Seamounts typically form from volcanic activity, and many host dramatic communities of sea life ‪—‬ from coral, to sharks, to an assortment of weird jellyfish-looking things.

How to use it in a sentence: Every time marine biologists explore a seamount with their remotely operated vehicles, they seem to discover a new universe of strange and blobby deep-sea creatures.

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Science word of the day: Pando

Pronunciation: PAN'-doh

What it means: In Latin, "Pando" means "I spread." And boy, does it. Pando is a clonal stand of aspen trees in Utah that weighs about 13 million pounds (6 million kilograms), making it the world's heaviest living organism ever found. Its 40,000 trees cover 106 acres (43 hectares) in Fishlake National Forest, and they're all connected by a single, sprawling root system. Some DNA analysis suggests that this many-fingered megatree is tens of thousands of years old.

How to use it in a sentence: When you walk through Pando, what seems like a normal stroll through an aspen grove is actually a trip through a single, ancient living being.

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Science word of the day: Cenozoic

Pronunciation: See-noh-ZOH'-ihk

What it means: The ascendency of mammals, the birth of the Himalayas, the diversification of birds ‪—‬ Earth's in its Cenozoic era, baby!

The Cenozoic is the geological era happening right now. It started 66 million years ago with the abrupt mass extinction known as the Cretaceous-Paleogene extinction event, when a massive asteroid hit Earth and wiped out the nonavian dinosaurs. It's been a busy few tens of millions of years, ushering in such hits as Earth's first cacti, whales and most (if not all) of the Grand Canyon.

How to use it in a sentence: The Cenozoic is called the Age of Mammals, but the University of California Museum of Paleontology in Berkeley would like you to know it could have been called the Age of Teleost Fish, if mammals weren't so dang self-centered.

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Science word of the day: Lithics

Pronunciation: LITH'-iks

What it means: In archaeology, lithics refers to artifacts made of stone. Scientists used to think Homo sapiens was the only human species to make stone tools. But like many oversimplified stories about human evolution, this one turned out to be a bust. Humans in Indonesia were making sharp-edge stone flakes 1.5 million years ago, before our species even existed.

How to use it in a sentence: Lithics preserve well, so scientists base a lot of what we know about ancient civilizations on their stone tools, while artifacts such as textiles or leather rot away.

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Science word of the day: Parsec

Pronunciation: PAHR'-sek

What it means: Ah, the humble parsec, thorn in the side of George Lucas. In 1977, Lucas' "Star Wars: Episode IV ‪—‬ A New Hope" script had Han Solo bragging that the Millennium Falcon completed the Kessel Run in less than 12 parsecs. The problem? Parsecs are a unit of distance, not a unit of time. This has caused angst among Star Wars fans for 49 years and counting.

But when we hit you with this definition, you're going to forgive Lucas for assuming the parsec was some sort of extra-fancy space second. Here it goes: A parsec is a unit of distance required to cause a heliocentric parallax of one arc second. Ouch.

Let's break it down. Heliocentric parallax is a way to measure the distance to a far-off object, such as a star, by measuring how it appears to move in comparison to another distant object (usually another star). An arc second is a fragment of an angle of an arc equal to 1/3600 of a degree.

This means a parsec is a unit of distance that makes a star seem to move 1/3600 of a degree compared with another distant star. It turns out that this equals 206,265 times the distance of Earth to the sun, or 3.26 light-years.

How to use it in a sentence: The 2018 movie "Solo: A Star Wars Story" tries to retcon Han Solo's brag about parsecs by claiming he was talking about distance all along ‪—‬ but we're not sure we're buying it.

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Science word of the day: Abiotic

Pronunciation: Ay-bye-AH'-tik

What it means: Abiotic means "without living organisms." Scientists typically use the term when referring to nonliving aspects of an ecosystem that affect organisms' growth or reproduction. Some abiotic factors might be light, water, fertilizer, nutrients or chemical elements, such as oxygen or sulfur. Others include the tides or rain. Sometimes, "abiotic" is used to describe the origin of a particular chemical. Abiotic methane, for example, comes from chemical reactions between rocks and water in Earth's crust, unlike biotic methane, which comes from decaying organic matter as well as microbes living in your gut.

How to use it in a sentence: A new "gold rush" of exploration is on for abiotic hydrogen, which forms when rocks react with water deep underground and could be a renewable, carbon-free fuel of the future.

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Science word of the day: Abiogenesis

Pronunciation: Ay-bye-oh-JEN'-ih-sis

What it means: Abiogenesis is the emergence of life from nonliving matter through chemical processes. Scientists still don't know exactly how abiogenesis happened on Earth. Theories range from lightning strikes that could have scrambled water, methane, ammonia and hydrogen into amino acids and sugars ‪—‬ the building blocks of life ‪—‬ to chemical reactions at deep-sea vents. Abiogenesis is not the same as spontaneous generation, which held that living organisms such as maggots formed directly from decaying matter. It was a compelling idea for anyone who had watched meat rot, but Louis Pasteur, inventor of pasteurization, disproved it in the 1860s by showing that microbes could only grow from preexisting microbes.

How to use it in a sentence: All life on Earth may owe itself to an incident of abiogenesis more than 3.7 billion years ago.

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Science word of the day: Cryptology

Pronunciation: Krip-TAH'-leh-jee

What it means: Cryptology is the study of secret codes ‪—‬ both making them (cryptography) and breaking them (cryptanalysis). Once associated with spy networks' secret codes and ciphers, cryptology now often refers to the computer algorithms used to encrypt data to protect passwords and personal information from prying eyes.

How to use it in a sentence: Native American soldiers known as "code talkers" harnessed cryptology in World War II by developing codes and ciphers based on their Indigenous languages.

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Science word of the day: Heliosphere

Pronunciation: HEE'-lee-uhs-feer

What it means: The heliosphere is the region around the sun that's affected by the solar wind, a flow of charged particles emanating from the sun. Think of the heliosphere like a giant bubble encompassing the sun and planets, reaching out into space at three times the distance of Pluto. This bubble protects the solar system from radiation emanating from outer space, but the solar wind can also erode planetary atmospheres. Luckily, Earth is protected by its own bubble, the magnetosphere, which helps deflect the solar wind.

How to use it in a sentence: Because the entire solar system is traveling through space, scientists have long pictured the heliosphere as comet-shaped, but recent research suggests the bubble of solar wind looks more like a sad, deflated croissant.

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Science word of the day: Autotroph

Pronunciation: AW'-tuh-trohf

What it means: Autotrophs are organisms that can feed themselves with inorganic substances such as light (for plants) or methane (certain microbes). Autotrophs were the first single-celled life-forms to colonize the planet, thriving on chemicals bubbling up from the subsurface at deep-sea vents or figuring out how to harness the sun for energy. Heterotrophs (like you, me and all fungi), arrived on the scene later to feast on these DIY-ers.

How to use it in a sentence: Stromatolites, microbial mats built by cyanobacteria, are autotrophs that thrived in ancient shallow seas.

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Science word of the day: Neuroplasticity

Pronunciation: Nur-roh-pla-STISS'-ih-tee

What it means: Neuroplasticity is the ability of the nervous system to adapt to the environment or to injuries by forming new connections and modifying and strengthening existing connections. Neuroplasticity can happen after an injury, such as a stroke or trauma to the brain, but it also occurs during ordinary learning. Just by reading this definition, you may be making new, sustainable brain connections.

How to use it in a sentence: Scientists used to think neuroplasticity was an ability only the the young had, but researchers are increasingly learning that aging brains can adapt throughout the lifespan, much to everyone's relief.

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