Our dynamic planet: Earth and life, Glossary 9780749288990, 074928899X

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S279 Our dynamic planet: Earth and life

Glossary for Book 2

acritarch Any small non-calcareous, nonsiliceous organic structure that cannot otherwise be classified. adiabatic From the Greek for ‘impassable’ – a reference to the fact that heat passes neither from or to a substance undergoing an adiabatic process. advection Transfer of heat by physically moving material. albedo The fraction of incoming solar radiation that is reflected from a surface. anoxic

Without oxygen, or oxygen poor.

aphelion The point on an orbit which lies furthest from the Sun. atmospheric window The range of longwave radiation leaving the Earth system between 8–13 µm where there is relatively little absorption. autotrophic Organisms that manufacture their own food. bacteria Very small, single-celled life forms: the most primitive living beings. bicarbonate ion (HCO3–) biogeochemical cycle Global cycling of an element used by organisms. biological pump The transfer of carbon from surface waters to the deep ocean. biolimiting Nutrients that can become completely used up by phytoplankton, thus preventing the growth of further organisms. biomes

Distinct ecosystem types.

biota All the plant and animal life of a region.

carbohydrates Sugars, starches, and cellulose, which contain C, H and O forming chains of simple sugars and which function primarily in energy storage, energy transport, and plant structure. carbonate compensation depth, CCD The depth in the ocean at which the proportion of calcium carbonate remaining falls to less than 20% of the total sediment. carbonate ion (CO32–). carbonate platforms plateaux.

Broad, shallow, submarine

carbonate system The reactions that occur between gaseous carbon dioxide and its various aqueous forms. carbon fixation A process found in autotrophs, usually driven by photosynthesis, whereby carbon dioxide is converted into organic compounds. chalk A distinctively fine-grained kind of limestone. chemical equilibrium A dynamic balance between forward and reverse reactions. Chloroplasts The organelles that effect photosynthesis in green plant cells. chromosomes Separate strands of genes, usually in pairs, contained in the nucleus of a cell. conduction Spread of heat energy through a solid, e.g. the heating of a saucepan handle when the pan is heated. convection The transfer of heat by circulation through a gas or liquid.

boundary layer The relatively still and humid layer of air next to the ground.

Coriolis effect The deflection of winds relative to the surface of the Earth resulting from the rotation of the Earth below air masses.

Cambrian Explosion The diversification of modern bilaterian life at the beginning of the Phanerozoic.

crown groups A group of closely related organisms which includes the common ancestor plus all its descendents.

Copyright © 2007 The Open University 1.1

cycads Plants that may represent the evolutionary link between ferns and flowering plants.

flood basalts Vast accumulations of horizontal basaltic rocks rapidly erupted from fissures over large areas.

decarbonation reactions A reaction during the heating of silicate and oxide minerals releasing CO2.

forcing function An external input to the Earth’s climate system.

diamicrite An unsorted mixture of rock that is of glacial origin.

gametes

Parental cells, e.g. eggs and sperm.

diploid Doubling up of chromosomes in the cell nucleus.

gene duplication The assignment of Hox genes to control the development of other body parts.

Ediacaran Period The last 70 Ma or so (610–540 Ma) of the Proterozoic.

GEOCARB model A model for the evolution of the carbon cycle and of atmospheric CO2 over geological time.

electromagnetic spectrum The ordered series of all known types of electromagnetic radiation, arranged by wavelength ranging from short cosmic rays through gamma rays, X-rays, ultraviolet radiation, visible radiation, infrared radiation, microwaves, to the long wavelengths of radio energy.

GSSP (Global Stratotype Section and Point) An internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic time scale. glossopterids Deciduous trees with distinctive tongue-shaped leaves.

endosymbiotic hypothesis The idea that organelles were once independent prokaryotes that took up symbiotic residence inside ancestral eukaryotic host cells.

Greenhouse effect The absorption of outgoing longwave radiation and the subsequent re-radiation that keeps the Earth’s average surface temperature at ~15 °C.

endothermic Reactions that require energy.

gross primary production (GPP) The total amount of carbon fixed via photosynthesis by plants.

epeirogenic changes See isostatic changes. eukaryotic cell A cell with a true nucleus as well as sub-cellular organelles.

gymnosperms The seed-bearing plants. Hadley circulation The latitudinal-vertical component of a helical circulatory system.

eustatic changes Worldwide sea-level changes that affect all oceans, e.g. due to the formation and melting of land ice.

halite pseudomorphs Casts of sediment filling often cube-shaped voids from which the original halite crystals had been dissolved.

evapotranspiration The process in plants whereby water drawn up from the soil by roots is lost to the atmosphere through pores in leaves.

haploid Cells containing only a single set of chromosomes.

evolutionary faunas Sets of major groups of animals, each set showing a characteristic pattern of family turnover.

herbaceous

Non-woody plants.

heterotrophic Organisms that consume organics or other organisms, whether plants of animals, to obtain energy.

evolutionary radiations Phases of significant increase in numbers of species within groups of organisms.

homeostasis Systems of self-regulation that maintain stable conditions within the organism in the face of a range of environmental perturbations.

exothermic Reactions that release energy. extremophile An organism that can tolerate, or requires, environmental conditions considered extreme to people.

hox genes Genes responsible for ‘pattern formation’ – that is, the overall arrangement of appendages – on the body of an organism.

false rings Tree growth rings found in fossils showing interruptions during the summer growing season.

hydrological cycle The movement of water that underpins the cycling of many other constituents through the Earth–atmosphere–ocean system.

fitness An individual’s production of offspring, themselves surviving to be capable of reproduction, relative to other individuals.

hyperthermophiles Organisms need high temperatures to grow (generally greater than 60 °C).

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intermediate scale (carbon cycle) Up to hundreds of thousands of years involving chemical, biological and physical components.

Milankovich cycles Changes in climate resulting from seasonal fluctuations caused by changes in elements of the Earth’s orbit, i.e. eccentricity, tilt of the rotational axis and longitude of perihelion.

Intertropical Convergence Zone (or ITCZ) The place where the wind systems of the two hemispheres meet.

mitochondria A eukaryote organelle responsible for the energy supply derived from aerobic respiration.

isostatic (or epeirogenic) changes Sea-level changes caused by vertical movements of the crust. Such movements may be caused by changes in the thickness and/or density of the lithosphere, and by loading or unloading with ice or sediments.

mitosis Cell division that conserves chromosome numbers in the nucleus. molecular clock theory The idea that as evolutionary lineages diverge from a common ancestor so too do their sequences as a consequence of cumulative mutational change in each lineage.

kerogen Dense residue enriched in carbon formed in an oxygen-poor environment. late Ediacaran 550 Ma ago.

molecular phylogenies Comparisons between organisms that use genetic sequences to determine how similar they are.

leaf margin analysis A widely used method that applies present-day correlations between the proportion of species with untoothed leaves and mean annual temperature to estimate palaeotemperatures from fossil megafloras.

mountain-forcing model A model that suggests changes in atmospheric CO2 concentrations are driven primarily by changes in chemical weathering rates.

leaf physiognomy The shape size and margin analysis of a leaf.

net primary production (NPP) The carbon that is not released back into the atmosphere via plant respiration.

lignin The carbon in plant structural material. long scale (carbon cycle) Geological timescale of up to hundreds of millions of years, involving rocks and sediments.

NLR (nearest living relatives) technique Assumes that ancient plants and plant communities lived under similar conditions to those of their nearest living relatives.

macrophagy The ability to ingest and digest food extracellularly by allowing the development of the gut.

nutrients Elements necessary for growth in a form that can be used by organisms.

mantle plumes Upcurrents of magma rising from the boundary between the mantle and the core, deep within the Earth

organelles Minute, intracellular structures serving a specific function in the life processes of the cell.

marine snow Clumps or aggregates of fluffy debris in the oceans made up of dead and dying algal cells and bacteria. mass extinction species.

particulate organic carbon (POC) Fragments of organic carbon, e.g. in soil.

World-wide extinction of many

perihelion The point on an orbit which lies closest to the Sun.

meiosis Cell division which halves the number of chromosomes, whilst also exchanging segments of DNA between the matching chromosome pairs of the diploid parents.

pH Hydrogen ion concentration in water, where a low pH corresponds to a high hydrogen ion concentration and vice versa. phloem The vascular tissue which enables movement of the products of leaf photosynthesis (such as sugars) to the rest of the plant.

mesoscale eddies Intermediate size eddies about 50–250 km across (i.e. about a quarter of the size of mid-latitude atmospheric cyclones and anticyclones). microfossils

photic zone The sunlit surface waters of the oceans.

Microscopic fossils.

photosynthesis The process undertaken by organisms to build their own organic material from CO2 and H2O, also producing O2.

midvein The main vein running through a leaf (also known as primary vein).

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physical erosion The break up of rocks e.g. by the action if ice, changes of temperature, that is not due to chemical change.

sessile An organism that does not move itself about and is often attached to a substrate. sexual reproduction The mixing together of genes from different individuals.

physiognomy The architecture of the plant or community applied when the fossils are in the form of vegetative organs, particularly leaves.

shocked quartz Quartz with microscopic deformation along planes, resulting from asteroid and comet impacts, i.e. intense pressure.

phytoplankton Minute floating algae: the primary producers of the oceans.

short scale (carbon cycle) Biological timescale of months/years to decades.

polar front The boundary between warm tropical air and the underlying cold polar air

snowball Earth The hypothesis that proposes that the Earth was entirely covered by ice in part of the Cryogenian and Ediacaran periods of the Proterozoic era, and perhaps also at other times in Earth history.

polar jet stream A high-level, fast air current that in each hemisphere flows around the Earth above the polar front. primary production The process of building living material by fixing carbon.

steady-state model A model that assumes that the system has attained equilibrium.

progymnosperms The woody dominant canopy formers in the earliest forests.

symbiont An organism that is associated with another in a mutually beneficial relationship.

prokaryotic cells Cells whose DNA is not bound into a nucleus and which lacks organelles

taphonomy The study of sedimentological and biological evidence relating to explanations of fossilization phenomena.

radiogenic strontium,, 87Sr The product of radioactive decay of one of the isotopes of rubidium, 87Rb.

taxa A taxonomic category or group, such as a phylum, order, family, genus, or species.

residence time A measure of the average length of time an individual molecule, e.g. water in the hydrological cycle, spends in any particular stage.

taxonomic hierarchy The classification of organisms into a nested series of increasingly inclusive groups (taxa) from species to kingdoms.

respiration The release, by organisms, of energy stored in organic matter.

tertiary veins Third series veins in a leaf that branch from secondary veins.

rhizoids Small root-hair-like appendages along rhizomes that anchored the planet to its substrate.

thermohaline The oceans’ deep temperaturesalinity circulation system.

rhizome The prostrate stem of early land plants.

transpiration The loss of water from a plant’s leaves.

rudists A group of bivalves that peaked in abundance and diversity during the late Mesozoic whose morphology consisted of a lower, roughly conical valve that was attached to the seafloor or to neighboring rudists, and a smaller upper valve that served as a kind of lid for the organism.

water masses Homogeneous bodies of water formed by deep mixing.

salinity The measure of concentration of dissolved salts.

xylem The primary water-conducting tissue in plants.

secondary veins Second series veins in a leaf that branch off the midvein.

zooplankton The animal component of plankton; animals suspended or drifting in the water column including larvae of many fish and benthic invertebrates.

troposphere The lower atmosphere, making up ~80% of the total mass of the atmosphere.

sedimentary succession Sequence of sedimentary strata. sensible heat Heat which can be felt, or sensed. sensitivity The size of the response of a system to a forcing of given magnitude.

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