The Universe, the Solar System, and the Origin of Life

A comprehensive vocabulary review of 50 key scientific terms and concepts relating to the Universe, the Solar System, planetary characteristics, and early life evolution.

Universe

Everything that exists: space, time, matter and energy.

The Big Bang

The beginning of the expansion of the Universe, which occurred about $13.8\text{ billion}$ years ago when the Universe was extremely hot and dense.

Ordinary matter

The component comprising $5\%$ of the Universe, consisting of stars, planets, gases and living things.

Dark matter

Invisible matter making up $27\%$ of the Universe that is detected through its gravitational effects.

Dark energy

The component making up $68\%$ of the Universe that is associated with the accelerated expansion of the Universe.

Galaxies

Systems of stars, gas and dust bound by gravity, including their planetary systems.

Nebulae

Clouds of gas and cosmic dust located in space.

Star clusters

Groups of stars in the Universe.

Binary stars

Two stars that orbit around each other.

Black holes

Celestial objects with extremely strong gravity.

Stars

Huge spheres of hot gas that form when gas and dust collapse under gravity, producing light and energy.

Nuclear fusion

A process in which atomic nuclei combine and release energy, such as converting hydrogen into helium.

Solar System

The planetary system formed approximately $4.5\text{ billion}$ years ago when gravity caused a nebula of gas and cosmic dust to collapse and rotate into a disk.

Heliocentric model

The astronomical model stating that planets orbit the Sun following elliptical orbits.

Aristarchus of Samos

The thinker who proposed an early heliocentric model in the 3rd century BC.

Copernicus

The astronomer who presented his heliocentric model in $1543$.

Galileo Galilei

The astronomer who provided important observational evidence supporting heliocentrism in the early 17th century.

Elliptical orbits

The paths followed by planets as they orbit the Sun.

The Sun

A yellow-orange star containing approximately $99.8\%$ of the Solar System's mass, composed mainly of hydrogen and helium.

Sun's core

The central part of the Sun reaching approximately $15\text{ million}\,^\circ\text{C}$, where nuclear fusion converts hydrogen into helium.

Solar wind

A stream of charged particles emitted by the Sun.

Planets

Bodies that orbit the Sun, are nearly spherical because of their gravity, and have cleared most other objects from their orbital neighbourhood.

Rocky planets

The inner Solar System group consisting of Mercury, Venus, Earth and Mars.

Giant planets

The outer Solar System group consisting of Jupiter, Saturn, Uranus and Neptune.

Dwarf planets

Bodies that orbit the Sun and are nearly spherical, but have not cleared their orbital neighbourhood, such as Pluto.

Satellites

Natural bodies that orbit planets or other celestial bodies, such as the Moon.

Asteroids

Small rocky bodies, many of which are located in the asteroid belt between Mars and Jupiter.

Asteroid belt

The region between Mars and Jupiter where many small rocky asteroids are found.

Comets

Bodies made mainly of ice, dust and frozen gases that often follow elongated orbits.

Coma

A cloud of gas and dust formed when a comet approaches the Sun and its ice releases material.

Comet tail

An extended stream of gas and dust formed when a comet approaches the Sun.

Meteoroid

A small rocky or metallic object traveling in space.

Meteor

The streak of light produced when a space object enters an atmosphere and heats up.

Meteorite

A fragment of a space object that reaches the ground.

Earth's magnetic field

A field that helps shield Earth's atmosphere from the solar wind and protects it from charged particles from the Sun.

Greenhouse effect

An atmospheric process that helps maintain temperatures suitable for liquid water on Earth.

Liquid water

A substance essential for the chemical reactions of life as we know it, maintained on Earth's surface by its distance from the Sun and atmosphere.

Aerobic respiration

A biological process that allows many organisms to release energy from nutrients using oxygen.

Chemical evolution

The gradual process proposed by Oparin in which life developed step-by-step from atmospheric gases to organic molecules and living cells.

Oparin's Theory

The theory (1924–1928) proposing that life developed gradually through chemical evolution in an early atmosphere with little or no free oxygen.

Primordial soup

The accumulation of organic molecules in the early oceans formed via lightning and ultraviolet radiation.

Coacervates

Organised molecular structures formed from organic molecules during chemical evolution that preceded living cells.

Miller–Urey experiment

A $1953$ experiment simulating proposed early-Earth conditions using gases and electrical sparks, demonstrating that organic molecules including amino acids can form abiotically.

Panspermia

The hypothesis proposing that life, or its chemical precursors, reached Earth from space via comets, asteroids, or meteorites.

Primitive atmosphere

The early atmosphere thought to contain mainly $CO_2$, $N_2$, and $H_2O$, which was likely not strongly reducing.

Hydrothermal vents

Ocean-floor environments that release hot water and chemicals, providing chemical energy that may have helped early life develop.

Hydrogen sulphide ($H_2S$)

A chemical substance released at hydrothermal vents that can act as a source of chemical energy for early life.

Cyanobacteria

Photosynthetic microorganisms associated with ancient stromatolites that released oxygen into the atmosphere.

Stromatolites

Structures associated with microbial communities that provide evidence of very ancient microbial life dating back more than $3.5\text{ billion}$ years.

Ozone layer

An atmospheric layer formed as oxygen increased that absorbs much of the Sun's harmful ultraviolet radiation.