Theropod (noun, “THER-oh-pod”)

Theropods are a group of dinosaurs. Their name means “beast-footed.” The group includes many extinct species, such as Tyrannosaurus rex and Velociraptor. It also includes modern birds.

Theropods first emerged about 230 million years ago. Early theropod species appear to have been mostly carnivorous. Over time, however, the group evolved into a diverse range of creatures. These included herbivores and omnivores. All non-bird theropods died out with the rest of the dinosaurs about 66 million years ago.

Theropods share certain characteristics, such as two legs, three forward-facing toes and hollow bones. Light, hollow bones allowed some members of the group to evolve flight.

Many extinct theropods sported feathers, scales or a mix of both. Yutyrannus huali was a dinosaur whose name means “feathered tyrant.” This species lived about 125 million years ago. It was one of the largest feathered species that ever lived. The oldest fossil of this species is about 10 meters (33 feet) long. These fossils show clear imprints of long feathers, which may have helped keep Y. huali warm.

All modern birds — from hummingbirds to emus to hawks — are theropods. Scientists learned this link between extinct dinos and modern animals thanks to theropod fossils. For instance, Archaeopteryx was a theropod that lived about 150 million years ago. Its hollow bones, clawed toes and feathers helped show how birds inherited features from their dino ancestors.

In a sentence

Famous dinosaurs such as Tyrannosaurus rex and Allosaurus were meat-eating theropods that stood on two legs.

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Pyrolysis (noun, “Py-RAW-leh-sis”)

Pyrolysis is a process though which heat breaks down large molecules into smaller ones. It is just one of the chemical reactions that occurs when something is burning.

Picture a campfire. The flame may look like a single chemical reaction. But in reality, it comes from multiple reactions that occur step by step.

The first step is pyrolysis. In this step, heat breaks open the fuel’s chemical bonds. In the case of a campfire, that fuel is wood. But pyrolysis doesn’t create the campfire’s flame. The next step — combustion — does that. Combustion occurs when the broken-open fuel molecules react with oxygen in the air.

Pyrolysis can occur without combustion. For example, if you seal wood in an oxygen-free container and heat it, the wood won’t ignite. Instead, pyrolysis will slowly transform it into charcoal. Pyrolysis typically does not break down fuel as completely as combustion does. That’s why charcoal can still burn to heat up a grill. In contrast, soot collected from a cold campfire typically cannot be burned.

Pyrolysis also plays a crucial role in cooking up a popular sweet treat: caramel.

To make caramel, a chef heats sugar and water on a stovetop into a syrup. As the syrup gets hotter and hotter, the sugar molecules begin to break open. This causes the clear syrup to turn yellow-gold and then a deep, caramel brown. That’s the chef’s cue to take the caramel off the heat. They may then add butter and cream to the hot, gurgling caramel. Much of the chemical transformation that turned syrup into caramel occurred through heat alone. Therefore, it is an example of pyrolysis.

In a sentence

Pyrolysis can produce biochar, a valuable, carbon-rich substance that farmers use to improve soil quality.

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