Geology Glossary
 
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  ash cloud. A cloud made of tiny particles of ash and smoke that fills the air during an explosive volcanic eruption.  
     
 

astrobiologist. A person who studies life on Earth and the possibilities for life in the universe.

  
     
 

astrobiology. The study of life in the universe.

  
     
 

atmosphere. The air. The blanket of gases that surrounds some planets and moons.

  
     
  atmospheric density. The weight of the air in a given part of the atmosphere.  
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  braided stream. A stream made of many channels that intertwine to look like a braid. Braided streams form when the stream has a large amount of sediment.  
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  caldera. A big crater or pit that forms when a volcano erupts or when the top of the volcano collapses.  
     
 

carbon dioxide. A colorless gas that can absorb heat in the atmosphere. Plants use carbon dioxide to make their food and animals exhale it when they breathe.

  
     
 

core. The center of a planet.

  
     
  cosmic rays. High-energy particles released when certain stars explode. Cosmic rays can be harmful to some life forms if they reach the Earth's surface.  
     
  crust. The outermost layer of a planet with a solid surface.  
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  dosimeter. A scientific instrument used to measure the amount of particle radiation in a certain area.  
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  erosion. The wearing away of a planet's surface by wind, water, or glacial ice.  
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  fault. A crack or break in the crust of a planet along which movement occurs.  
     
  flow channel. The path of a river or stream along which water flows as it makes its way downhill.  
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  geologist. A person who studies Earth's origin, history and structure.  
     
 

geology. The study of Earth's origin, history and structure.

  
     
 

geomorphologist, A person who studies the surface features of a planet and the processes that created them.

  
     
 

geophysicist. A person who uses physics to study the inside of a planet and other characteristics of a planet that cannot be investigated directly, such as the planet's magnetic field and gravity.

  
     
 

greenhouse effect. Some gases, such as carbon dioxide and water vapor, absorb heat energy and release it in the atmosphere raising the surface temperature of a planet.

  
     
  greenhouse gas. A gas that traps heat energy and releases it in the atmosphere. The main greenhouse gases are: carbon dioxide (CO2), water vapor (H2O), methane (CH4), nitrous oxide (N2O), and the human-made chlorofluorocarbons (CFCs).  
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  habitability. The extent to which an environment is fit to live in.  
     
 

habitable. Fit to live in.

  
     
  hypothesis. An educated guess that scientists make to predict an answer to a question.  
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  impact crater. A pit or depression on a planet's surface that forms when a meteorite strikes the planet.  
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  lava flow. Lava that oozes, like syrup, from the top of a volcano, down its sides, and onto the ground. Lava flows are formed by volcanoes like those of the Hawaiian Islands that do not have violent, explosive eruptions.  
     
 

lithosphere. The rigid layer formed by the crust and uppermost part of the mantle that moves together as plates on top of the Earth's surface. The lithosphere rides on top of the asthenosphere.

  
     
 

lunar highlands. The light-colored regions of the moon that are composed of the rock type called anorthosite and have a higher elevation than the lunar mare.

  
     
  lunar mare. The dark-colored regions of the moon that composed of huge lava flows. From the Earth, they look like seas, or "mare," the Latin word for sea.  
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  magnetic field. Area surrounding magnets that deflects charged particles or other magnets.  
     
 

magnetometer. An instrument used to detect small changes in a planet's gravity to measure its magnetic field. The changes are measured in units of nanotesla.

  
     
 

main channel. The largest river or stream in a river system into which all of the smaller branches, or tributaries, flow into.

  
     
 

mantle. The part of a planet between the crust and the core.

  
     
 

mass. The amount of matter in an object.

  
     
 

meander. A bend in a stream or river.

  
     
 

meteorite. A rock from space (meteor) that passes through the Earth's atmosphere and lands on the Earth.

  
     
 

millirad (mrad). The unit used to measure the amount of radiation present in an object or area. The prefix "milli" means one-thousandth.

  
     
  mutation. A change in the DNA of a living thing,  
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  nanotesla (nT). The unit used to measure the strength of a magnetic field. The prefix "nano" means one-billionth.  
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  particle. A basic unit of matter or energy.  
     
 

periodic. Occurring regularly or repeatedly over time, like a cycle.

  
     
 

plate. A large, rigid segment of Earth's lithosphere that moves in relation to other plates over the mantle.

  
     
 

positive feedback loop. A feedback loop is a cycle of inputs and outputs. The feedback loop is balanced when the input equals the output. Positive feedback occurs when the output is bigger than the input. A positive feedback loop speeds up the cycle in the direction of the output, and throws the cycle out of balance.

  
     
  positive relief. Term used to describe the elevation of features on a planet's surface that are higher than the ground surrounding them.  
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  radar. A way to find or track objects using radio waves. An instrument sends out radio wave signals. The signals reflect off of the object and bounce back to the instrument, which uses the signals to locate the object.  
     
 

radar topography. Measures the elevations on the surface of a planet by sending radar signals down to the planet's surface and detecting how long they take to bounce back to the spacecraft. Radar topography provides a way to discover what a planet's surface looks like without actually going there.

  
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  solar wind. Particles that move away from the sun at high speeds. The solar wind is deflected by Earth's magnetic field.  
     
 

space radiation. Charged particles that can cause mutations or death in most life-forms. Space radiation in our solar system comes from the solar wind and from nearby exploding stars.

  
     
  structural geologist. A person who studies the deformation of a planet that is caused by faulting and folding of a planet's crust.  
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  tributary. A small stream or branch of a river that flows into a larger river or lake.  
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  volcanologist. A person who studies volcanoes.  
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  water vapor. The form water takes when it is a gas in the atmosphere.  
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