Featured Answers

Active contributors today


Multiple things, depending on the context of the question.


Personally, I define gneiss as a foliated metamorphic rock that most commonly is formed from shale (through a series of other transformations), as a result of regional metamorphism (formed under a lot of pressure and heat, over a fairly large area). Additionally, it usually has a banded appearance, which isn't unique among metamorphic rocks, but it does help it separate it from the non-banded rocks.

Most people can't legitimately say that gneiss can be defined by its composition, because it varies, but most gneiss samples will have bands of quarts (silicon dioxide) and feldspar (silica and aluminum containing). As a result, I don't primarily define gneiss from its chemistry.

Sometimes it's nice to see it compared to other rocks to help choose your own path to its definition. Below is an ID chart used to determine the rock type of some popular metamorphic rocks.

Black Hawk College

Here are some different gneiss rock samples, just to show you the variation:



The University of Auckland


Earth's four spheres are: the lithosphere , the atmosphere , the hydrosphere , and the biosphere .


Every thing on Earth can be placed in one of the four major subsystems or spheres.

The Lithosphere refers to the land mass which includes all forms of terrestrial structures and zones.

The Atmosphere refers to the blanket of air that covers the air which is itself divided into subspheres: the troposphere, the stratosphere, the mesosphere, and the thermosphere which contains the ionosphere and the exosphere.

The Hydrosphere refers to all water bodies, liquid and frozen (sometimes called the cryosphere), salt and fresh, surface or underground.

The Biosphere refers to all living creatures that exist.



When the location is angled towards the sun, it gets longer days and higher temperatures. When angled away, days are shorter and cooler.


The earth rotates on an axis but the North-South axis is not "vertical" but tilted slightly. As the earth orbits the sun, the axis doesn't change.

The Northern Hemisphere faces the sun while the Southern Hemisphere is facing away from the sun. Temperatures north of the equator will be higher and the days will be longer.

The Northern and Southern Hemispheres face the sun equally.

The Northern Hemisphere faces away from the sun while the Southern Hemisphere faces toward the sun. Temperatures north of the equator will be lower and days will be shorter.

The Northern and Southern Hemispheres face the sun equally.


More info: NASA SpacePlace


The East Coast of North America is a passive tectonic margin; whereas, the West Coast is an active margin.


The East Coast is currently a passive margin where the North American Plate is moving slowly away from the European Plate. On the West Coast however, several plates are interacting to cause frequent earthquakes and volcanism. In California, The North American Plate and Pacific Plate are moving past each other along a transform margin (the San Andreas Fault System).

In the Pacific Northwest, the Juan de Fuca Plate is being subducted beneath the North American Plate at the Cascadia subduction zone. (See below) The result is the string of active volcanoes (the Cascades) that extends from Northern California to southern Canada, including Mt. St. Helens and Mt. Ranier. i.ytimg.com


Generally speaking, there are five types of sand dunes: transverse, linear/longitudinal, star, barchan, and parabolic.


Sand dune types are determined by shape. The shape of a sand dune is dependent on the strength of the wind and on the sand type.

Generally speaking, there are five types of sand dunes: transverse, linear/longitudinal, star, barchan/crescentic, and parabolic/blowout .

The five main types of dunes are shown below.

Wind coming from all directions generates star dunes.

Barchan and parabolic dunes can look very similar but the main difference is the direction of the wind in relation to the top of the crescent shape. The top of the crescent faces the wind direction in barchans and the top of the crescent is orientated in the same direction as the wind in parabolic dunes.

The direction of the wind also creates the main difference between transverse and linear dunes.


Please see explanation below.


Carbon Cycle:

  • There are many important processes in the carbon cycle that primarily relate to photosynthesis, decomposition, and deposition.
  • #CO_2# is absorbed by various plants and vegetation and converted into carbohydrates via photosynthesis.
  • Carbon travels through the food chain and eventually makes its way into the atmosphere via cellular respiration, burning of fossil fuels, or decay of organisms.
  • Carbon travels from the ground to the atmosphere
  • Fixation of carbon is carried out by living organism including plants and animals.

University of Waikato

Nitrogen Cycle:

  • Has the processes of mineralization, nitrification, and denitrification.
  • Nitrogen fixation occurs from converting Nitrogen gas (#N_2#) into ammonia (#NH_3#).
  • Nitrogen is sent to the ground.
  • The nitrogen cycle takes place in Earth's various "spheres" (geosphere, atmosphere, and biosphere).
  • All stages of the nitrogen cycle are carried out by various microorganisms.



  • Both are biogeochemical cycles that release their respective element into the atmosphere.
  • The carbon and nitrogen cycles work together and can often be referred to as the CNO cycle.
  • Both start as a gas and end as a gas.
View more
Ask a question Filters
This filter has no results, see all questions.
Question type

Use these controls to find questions to answer

Need double-checking
Practice problems
Conceptual questions