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Unit 1: Many Planets, One Earth // Glossary

The fraction of electromagnetic radiation reflected after striking a surface.
A major division of microorganisms. Like bacteria, Archaea are single-celled organisms lacking nuclei and are therefore prokaryotes, classified as belonging to kingdom Monera in the traditional five-kingdom taxonomy.
Microscopic organisms whose single cells have neither a membrane-bounded nucleus nor other membrane-bounded organelles like mitochondria and chloroplasts.
Cambrian explosion
Between about 570 and 530 million years ago, when a burst of diversification occurred, with the eventual appearance of the lineages of almost all animals living today.
An ion with a positive charge.
A phylum of Bacteria that obtain their energy through photosynthesis. They are often referred to as blue-green algae, although they are in fact prokaryotes, not algae.
A single-celled or multicellular organism whose cells contain a distinct membrane-bound nucleus.
Microorganisms belonging to the domains Bacteria and Archaea that can live and thrive in environments with extreme conditions such as high or low temperatures and pH levels, high salt concentrations, and high pressure.
geochemical cycling
Flows of chemical substances between reservoirs in Earth’s atmosphere, hydrosphere (water bodies), and lithosphere (the solid part of Earth’s crust).
An organism that requires organic substrates to get its carbon for growth and development.
negative feedback
When part of a system's output, inverted, feeds into the system's input; generally with the result that fluctuations are weakened.
An array of reactions involving several different types of chemical conversions: (1) loss of electrons by a chemical, (2) combination of oxygen and another chemical, (3) removal of hydrogen atoms from organic compounds during biological metabolism, (4) burning of some material, (5) biological metabolism that results in the decomposition of organic material, (6) metabolic conversions in toxic materials in biological organism, (7) stabilization of organic pollutants during wastewater treatment, (8) conversion of plant matter to compost, (9) decomposition of pollutants or toxins that contaminate the environment.
The largest generally accepted groupings of animals and other living things with certain evolutionary traits.
plate tectonics
A concept stating that the crust of the Earth is composed of crustal plates moving on the molten material below.
Organisms without a cell nucleus, or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular. The prokaryotes are divided into two domains: the bacteria and the archaea.
radiometric dating
A technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. It is the principal source of information about the age of the Earth and a significant source of information about rates of evolutionary change.
Snowball Earth
Hypothesis that proposes that the Earth was entirely covered by ice in part of the Cryogenian period of the Proterozoic eon, and perhaps at other times in the history of Earth
stratigraphic record
Sequences of rock layers. Correlating the sequences of rock layers in different areas enables scientists to trace a particular geologic event to a particular period.
The process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other.

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