If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

All of the following terms appear in the videos or articles for this tutorial on global threats to biodiversity. The terms are arranged in alphabetical order, and nouns are given in just their singular form unless the plural of the term is unusual.

acidic: any liquid or substance with a pH less than 7

alkaline: any liquid or substance with a pH greater than 7; same as basic

atmosphere: the mixture of gases surrounding a planet such as Earth, held in place by gravity

average global temperature: the calculation of Earth’s average temperature over the course of one year; it is difficult to calculate due to the size of the planet and large areas where no temperature data are available, but various scientific organizations have established consistent methods that allow for comparison from year to year to detect changes

atoll: a ring-shaped coral reef with low-lying islands that encircle a central lagoon; usually there are one or more channels that connect the lagoon with the surrounding ocean

basic: any liquid or substance with a pH greater than 7; same as alkaline

bicarbonate: \text{HCO}_3- ; also called hydrogen carbonate; associated with the process of ocean acidification -- as carbon dioxide dissolves in sea water some of it is converted to carbonic acid which in turn is converted to bicarbonate and hydrogen ions

biodiversity: the variety of life on Earth or some specified geographic area of the planet; the diversity of life occurs at the genetic level, at the species level, at the ecosystem level, and in evolutionary lineages 

biogeography: the study of how species are distributed on Earth

biosphere: the part of Earth where organisms live; all of the ecosystems on Earth

buffer: in general, something that prevents or minimizes a stress or change; in chemical terms, a substances that stabilizes, or prevents changes in, pH

calcium carbonate: \text{CaCO}_3; a white, insoluble solid that occurs naturally in certain types of rock such as chalk, limestone and marble, and is secreted by animals as a main component of coral and echinoderm skeletons, shells of mollusks and crustaceans, pearls, and bird eggshells

carbon\text{C}; a naturally abundant element that, in combination with at least one hydrogen atom, occurs in all organic compounds and therefore in all known forms of life; also found in many inorganic molecules such as carbon dioxide (\text{CO}_2) and carbon monoxide (\text{CO})

carbon cycle: the movement of carbon between and within the atmosphere, living organisms, bodies of water, rocks and sediments

carbon dioxide: \text{CO}_2; occurs naturally in Earth’s atmosphere and is one of the main greenhouse gases; amount is increasing since \text{CO}_2 is a by-product of burning fossil fuels

carbon footprint: a calculation of the total amount of greenhouse gas emissions produced by a person’s daily activities such as driving, running household appliances, the type of food eaten, and airplane travel

carbonate: an adjective used to describe a substance composed largely of carbonate ions

carbonic acid: \text{H}_2\text{CO}_3; a weak acid formed when carbon dioxide dissolves in water; in sea water, the dissolving of carbon dioxide is associated with ocean acidification

chemical reaction: a process in which two or more types of chemical compounds or elements react and are converted into one or more new types of compounds

climate change: the global or regional change in temperature, precipitation, or wind patterns, among others, that occurs over several decades or longer

coccolithophore: a single-celled, microscopic, marine phytoplankton that produces calcium carbonate shells

fixation: in a chemical context, a biochemical process that converts an inorganic substance into an organic substance or a substance more readily used by living organisms; carbon fixation converts carbon dioxide into organic compounds

food web: the collection of all the food chains in an ecosystem that describe who eats what, and represents the flow of energy and nutrients in that ecosystem

foraminifera: single-celled marine animals with shells ranging in size from microscopic to almost 20 cm (8 inches); shells often made of calcium carbonate; abbreviated to "forams"

fossil fuel: a non-renewable energy source such as oil, natural gas and coal; formed over millions of years from the decomposition of buried, dead organisms

global change: a term that encompasses climate change, but also other drivers of environmental change that can interact with climate change, such as land use change, alteration of the water cycle, changes in biogeochemical cycles, and biodiversity loss

global warming: a rise in Earth’s average global temperature; the relatively recent and ongoing warming is caused by increasing concentrations of greenhouse gases in the atmosphere, especially carbon dioxide

greenhouse gas: any gas in Earth’s atmosphere that absorbs solar radiation and traps it as heat; although greenhouse gases can be naturally occurring compounds (such as water vapor, carbon dioxide, methane, and nitrous oxide), an excess of such gases, in conjunction with artificially produced gases (such as those used in some aerosol sprays) can cause excessive atmospheric warming that threatens biodiversity

hydrocarbon: a compound containing only hydrogen and carbon; the majority of naturally occurring hydrocarbons on Earth are found in fossil fuels

hydrosphere: all of the water on our planet

hypercapnia: a medical condition in which there is an abnormally elevated level of carbon dioxide in the blood or body fluids of an organism

infrared: electromagnetic radiation with wavelengths longer than that of visible light; also known as heat

ion: an atom or molecule in which the total number of electrons is not equal to the total number of protons, thus giving it a net positive or negative electrical charge

larva: the immature stage of an animal that does not look like the adult stage; undergoes a significant change or metamorphosis to assume the adult form (e.g., caterpillar becoming a butterfly); plural = larvae

lithosphere: the rigid outermost layer of a planet; on Earth, consists of the crust and upper mantle

logarithmic scale: a measurement scale in which the intervals between units correspond to orders of magnitude rather than a standard linear scale

methane: \text{CH}_4; one of the greenhouse gases; a primary component of natural gas

mollusk: the biological group of animals such as snails, clams, and squid that have a soft body without a backbone, and usually have a shell; an extremely large and diverse group including marine, freshwater, and terrestrial representatives

ocean acidification: a decrease in the average pH of the ocean (i.e.,, an increase in the ocean’s acidity) due to the dissolving of atmospheric carbon dioxide in seawater, which in turn drives chemical reactions that produce acid

ozone: \text{CO}_3; an inorganic gas; found in the upper atmosphere where it helps block ultraviolet radiation, but acts as a pollutant in the lower atmosphere; also used commercially for a variety of purposes

Paleocene/Eocene boundary: the time period about 56 million years ago at the end of the Paleocene epoch and the beginning of the Eocene epoch

\text{pH}: a measure of the acidity of a solution; described on a scale ranging from 0 (most acidic, least basic or alkaline) to 14 (most basic or alkaline, least acidic); \text{pH} 7 is neutral (neither acidic nor basic) and is the \text{pH} of distilled water; \text{pH} is measured on a logarithmic scale

photosynthesis: the process of capturing the energy in sunlight to create energy-rich organic molecules from inorganic molecules; organisms that photosynthesize are called photosynthesizers

plankton: microscopic organisms that live in the ocean and other bodies of water; phytoplankton are plant-like and can photosynthesize; zooplankton are animal-like and cannot photosynthesize

producer: an organism, such as a plant, that can make its own energy-rich food molecules

rate: a measure of how something varies with the passage of time

respiration: the process of breathing in living organisms in which oxygen is taken in and carbon dioxide is released; cellular respiration refers to the metabolic process by which all living organisms break down energy-rich organic compounds to meet their energy needs and carry out life functions

sequestration: in general, to seclude or withdraw; in the carbon cycle, the process by which carbon is removed from the atmosphere and stored somewhere else, such as in the body of plants via photosynthesis

solar radiation: the radiant energy emitted from the sun

statolith: a structure found in the sensory receptor of many aquatic invertebrates, including mollusks, echinoderms, and crustaceans, that helps the organism maintain balance

water vapor: water in the gas phase rather than liquid or solid; water vapor is common in Earth’s atmospshere