Atom	A small unit of matter composed of protons, electrons, and usually neutrons. Atoms are basic building blocks of the matter we see in the Universe and on Earth. The number of protons in the nucleus of an atom determines which chemical element it is.
Big Bang	A theory, first articulated in the 1920s, proposing that the Universe started out extremely hot and dense and gradually cooled off as it expanded.
Big History	A unified account of the entire history of the Universe that uses evidence and ideas from many disciplines to create a broad context for understanding humanity; a modern scientific origin story.
Black Hole	A region in space of such high density that its gravitational pull does not even allow light to escape. Black holes can be formed by the collapse of large objects such as very large stars.
Chemistry	The scientific study of elementary forms of matter and the interactions between them.
Climate Change	Measurable changes in the climate over long periods of time.
Collective Learning	The ability to share, preserve, and build upon ideas over time.
Complexity	A quality of an object or system that has diverse components precisely arranged in connection with one another (so that new properties emerge which did not exist in the components alone).
Democracy	A system of government based upon majority decisions made by voting citizens.
DNA (deoxyribonucleic acid)	The double-stranded molecule, present in all living cells, that contains the genetic information used to form and maintain the cell and passes that information to offspring cells.
Earth	The third planet from the Sun in our Solar System, home to many complex life forms and modern human society.
Energy	The capacity to do work, associated with matter and radiation. Includes kinetic energy, potential energy, and chemical energy, among others.
Entropy (the law of)	The natural tendency of all things to move from order to disorder. (Note: Although often called the law of entropy, it is more accurate to refer to it as the second law of thermodynamics.)
Fossil Fuel	A carbon-based material such as coal, oil, or natural gas that can be used as an energy source. Fossil fuels were originally formed when the remains of living organisms were buried and broken down by intense heat and pressure over millions of years.
Global Warming	The increase in average global temperature caused by high quantities of carbon dioxide in the atmosphere.
Globalisation	The expansion of exchange networks until they begin to reach across the entire world.
Goldilocks Conditions	Specific set of conditions necessary to enable greater complexity. The reference is to the fairy tale Goldilocks and the Three Bears, in which Goldilocks looks for the porridge, chair, and bed that are "just right."
Gravity	The fundamental force of attraction between any two objects that have mass.
Greenhouse Effect	A process by which certain trace gases in the Earth’s atmosphere trap heat near the Earth’s surface and so keep the Earth’s climate warmer than it would be otherwise. The Earth emits some of the radiation it receives from the Sun back into space, but greenhouse gases trap some of this radiation before it can escape, thus warming up the climate on Earth, as in a greenhouse.
​​Homo sapiens	The scientific name for our species, which is thought to have evolved in Africa between 200,000 and 300,000 years ago.
Individualism	The emphasis of the importance of the individual’s freedoms and needs over those of the collective group.
Life	Four commonly accepted attributes of life are that it uses energy from the environment by eating or breathing or photosynthesizing (metabolism); it makes copies of itself (reproduction); over many generations it can change characteristics to adapt to its changing environment (adaptation); and it can regulate internal conditions in order to maintain a stable state (homeostasis).
Milankovitch Cycles	The emphasis of the importance of the individual’s freedoms and needs over those of the collective group.
Solar System	The Sun and the objects that orbit it; the area in space in which the Sun’s gravitational pull is the dominant force.
Star	A huge cloud of simple matter held together by gravity. The star, the first complex entity in the Universe, has structure, stability, and sustained energy flow due to nuclear fusion at its center.
Supernova	The explosion of a massive star at the end of its life; most chemical elements are created by supernova explosions.
Supersymmetry	An extension of the Standard Model of particle physics (which states that all matter is made up of basic building blocks), supersymmetry predicts a partner force particle for each of those matter particles described in the Standard Model (for example, a selectron for every electron, a squark for every quark).
Thresholds of Increasing Complexity	Moments in the history of the Universe when specific ingredients under the right "Goldilocks Conditions" come together to create something new and more complex.
Universe	All the matter and energy in existence, as well as the space that contains it.