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Term Term description

Ancient Egyptian Sun god.


Energy radiated in the form of waves or particles, for example energy from the sun is called solar radiation and is divided into infra-red, visible and ultra violet according to the wave length of the radiant energy emitted.


The release of energy from an unstable atom in the form of gamma rays, alpha or beta particles, or conversion electrons. There are many naturally occurring radioactive materials, most of which do not release enough energy to be harmful. However, exposure to high levels of radiation can cause DNA to mutate, leading to cancer or death. Humans have produced highly radioactive materials for weapons and energy production, and these concentrated sources of radiation can be very dangerous.

radioactive decay

The spontaneous transformation of an unstable atomic nucleus into a lighter one, in which radiation is released in the form of alpha particles, beta particles, gamma rays, and other particles. The rate of decay of radioactive substances such as carbon 14 or uranium is measured in terms of their half-life.

radioactive uranium

A radioactive silvery-white metallic element. It occurs in several minerals including pitchblende, carnotite, and autunite and is used chiefly as a source of nuclear energy by fission of the radioisotope uranium-235.


The distance from Earth's center to its surface, about 6,371 kilometers (3,959 mi).

rain shadow desert

The desert areas that occur on the leeward side of mountain ranges whose windward side is often wet and lush with vegetation. For example, on the Pacific coast of North America in the Sierra Nevada Mountains, as warm, moist air blowing eastward from the ocean moves up the windward side of the mountain, it cools and condenses as it rises in altitude, and drops its moisture as rain. As the wind continues moving eastward over the top of the mountain range and down the other side, the leeward side of the mountain receives only dry air that  has lost its moisture, and this forms a desert.

range of tolerance

The range of conditions within which an organism is potentially able to survive. For example, all organisms have a maximum and minimum level of temperature, atmospheric pressure, oxygen concentration etc. within which they can survive.

recessional agriculture

A form of agricultural cultivation that takes place on a floodplain. Crops are planted in the flooded areas after the waters recede.


In a religious sense, the experience of being saved from or changed out of a life of suffering caused by one’s immoral or sinful actions.

reduced tillage

A farming practice which involves fewer cultivations than used in conventional fallowing.


The social expression of an experience of a God, gods, spiritual power in the form of community organization, worship, and shared beliefs and moral practices.


Replaced or replenished naturally in the same amount or less time as it takes to draw the supply down.

reproductive isolation

Barriers (geographical, behavioral, biological) that prevent gene flow between members of a species.


The systematic investigation into and study of materials and sources in order to establish facts and reach new conclusions.


A natural or artificial pond or lake used for the storage of water, often times constructed by damming a river and backing up water flow for hydro-electric energy production and/or downstream flood control.


The ability of an ecosystem to recover to its pre-disturbance state following a disturbance.


The capacity of an ecosystem community, organism, tissue, or cell to withstand the effects of a physical, chemical or biological disturbance, such as a hurricane, oil spill or pathogenic infection.


Cellular respiration is the process by which the chemical energy of "food" molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is most commonly used as an example to examine the reactions and pathways involved.

restoration ecology

An applied science; the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.

restorative justice

Restorative justice is a theory of justice that emphasizes repairing the harm caused or revealed by criminal behaviour.

retention time

The length of time an atom or molecule, whether solid, liquid or gas, persists in a given place. For example, a carbon atom in the form of carbon dioxide will be retained in the atmosphere until absorbed into the ocean or taken up by a plant for photosynthesis. A water molecule will have a shorter retention time if part of a puddle on a sidewalk than in a deep lake.

reverse osmosis

A water purification technology that uses a semipermeable membrane to remove dissolved solutes from water. It can be used to desalinate seawater.


A nitrogen-fixing bacterium that is common in the soil, especially in the root nodules of leguminous plants.

right to water

A formal, international law related to the access to water and sanitation needed by human beings for the full expression of dignity. The right to water requires that all people enjoy access to sufficient, safe, accessible, and affordable water without discrimination, for personal and domestic use.



The basic rights and freedoms to which all humans are morally entitled, held to include such moral powers as the right to life and liberty, freedom of thought and expression, and equality before the law.

rill erosion

Removal of soil by running water with formation of shallow channels that can be smoothed out completely by normal tillage.


The wet habitat located on the bank of a natural watercourse (as a river) or sometimes of a lake or a tidewater.


In a religious sense, a traditional and meaningful series of actions performed according to a prescribed order that serve to bring the participants in close relationship with the source of their religious experience.


(Ribonucleic acid) The nucleic acid that is used in key metabolic processes for all steps of protein production in all living cells. Unlike double-stranded DNA, RNA consists of a single strand of nucleotides, and it occurs in a variety of lengths and shapes.

rock-forming materials

Any mineral that forms igneous, sedimentary, or metamorphic rocks. Examples include quartz, feldspar, mica, and olivine.

Roman Catholic Church

A Christian church founded on the teaching and life of Jesus Christ and characterized by sacramental worship, multiple traditions of spiritual practice, and hierarchical authority exercised by the Pope in the Vatican and bishops throughout the world.


Rūḥ is an Arabic word meaning spirit, and appears to be related to the Hebrew word "Ruach" or "Ruah".


An animal such as a cow or sheep that has more than one stomach and that swallows food and then brings it back up again to continue chewing it. Their multiple stomachs help them efficiently digest plant material with the help of microbes.


Precipitation, snow melt, or irrigation water that runs over land and into  surface streams, rivers, drains or sewers.

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