Actinides
Actinides are a group of fifteen metallic elements (atomic numbers 89–103) that are radioactive, electropositive, tarnish if exposed to air, and release hydrogen by reacting with water. The fifteen elements are actinium, thorium, proactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium.
Anoxic
Refers to an environment with low or no oxygen.
Atmospheric aerosols
Very small drops of liquid or solid particles (generally smaller than one micron) that remain suspended in the air, including soot aerosols (from fossil fuel combustion), volcanic aerosols, and soil-dust aerosols.
Auxiliary stratotype
A stratotype is the specific stratal sequence used for the definition and/or characterization of the stratigraphic unit or boundary being defined. While the Global Boundary Stratotype Section and Point (GSSP) is the internationally agreed reference point for a geological time unit, auxiliary stratotypes in other locations may provide further information that backs up the boundary shown by the GSSP.
Benthic organisms
Organisms that live at the bottom of a body of water, on or in the bottom sediments (in a sea or lake bed).
Biomass
The total mass of living organisms in an environment at a given time.
Block
A block is a mass of rock or other matrix maintaining its original structure.
Bomb pulse
The sudden increase of carbon-14 in the Earth’s atmosphere due to the hundreds of atmospheric nuclear bomb tests that started in 1945 and intensified after 1950 until 1963, when the Limited Test Ban Treaty was signed by the United States, the Soviet Union and the United Kingdom. Since then 123 other states have joined the treaty.
Brackish
Brackish water is saltwater that is not as salty as seawater, often produced by the mixing of sea and freshwater in environments such as estuaries or by evaporation of freshwaters containing dissolved salts.
Catchment
The area drained by a river or other water courses.
Chrysophyte
Chrysophytes are golden or golden-brown algae (mainly found in freshwater) with carotenoid pigments (responsible for their color) alongside chlorophylls.
Continental shelf
The area of the seafloor that extends from a continent’s shore to a depth of around 150–200 meters.
Coral bleaching
Coral bleaching occurs when corals are stressed by changes in environmental conditions including temperature and pollution levels. The coral expels the algae that usually gives it its color, revealing the white calcium carbonate skeleton. Corals can regain their algae if conditions improve, but increasing incidence of environmental stressors leave less time for corals to recover in between bleaching events.
CT scan
A CT scan or CAT scan is an image produced using computerized axial tomography, which combines a series of X-ray images taken from different angles.
DDT
Dichlorodiphenyltrichloroethane (DDT) is a highly toxic chemical compound first synthesized in 1874 by the Austrian chemist Othmar Zeidler. After its insecticidal properties were discovered in 1939, it was widely used as an agricultural and household pesticide. Rachel Carson’s 1962 book Silent Spring documented its destructive environmental impacts and sparked opposition to its use. It was banned in the US in 1972 and a worldwide ban on agricultural use has been in force since 2004.
Diatom
A diatom is a microscopic single-celled algae with a shell-like cell wall (called a frustule) made of silica. They live in nearly all bodies of salt and freshwater.
Eutrophication
An excessive growth of algae and other plants feeding on increased input of nutrients, which in turn causes a depletion of oxygen and reduction in animal life.
Event stratigraphy
Event stratigraphy is the study of traces of geologically short-lived events (from instantaneous to millions of years). Events may be represented by depositional, erosional, fossil, geochemical features, and may be local, regional, or global in scale.
Exoskeleton
An external skeleton.
Fluorescence
The emission of light and other radiation after the absorption of electrons or radiation of a different wavelength, especially ultraviolet light and x-rays.
Foraminifera
Foraminifera are a diverse group of single-celled marine organisms with a shell made of calcium carbonate. They live in a variety of habitats and have a diverse range of forms, and their fossils can be used to reconstruct past environments.
Frustule
Frustules are the shell-like cell walls of diatoms, made of silica.
Golden spike
A golden spike is an informal term for a Global Boundary Stratotype Section and Point (GSSP), which refers to the spike that may be driven into rock to mark the lower boundary of a geological time unit.
GSSP
A GSSP is a Global Boundary Stratotype Section and Point, which defines the lower boundary of a chronostratigraphic unit on the geologic time scale. It is sometimes referred to as a “golden spike”, after the marker which is, in some cases, driven into the boundary.
Halocline
A layer in a body of water where salinity and density sharply change.
HCH
Hexachlorocyclohexane (HCH) is any one of a group of organic compounds with a six-carbon ring with one chlorine and one hydrogen attached to each carbon. HCHs have poisonous, pesticidal, and persistent organic pollutant properties.
Holocene
The current geological epoch, beginning around 11,700 years ago, and characterized by a relatively stable climate that allowed major human civilizations and the modern world to develop.
Hypoxia
Depletion of dissolved oxygen in water and sediments.
Ice flow
The movement of ice deforming under the force of gravity.
Karstic
Refers to a region which is underlain by porous limestone and which has landforms produced by dissolution and underground drainage systems (such as karst towers, caves, and sinkholes).
Last Glacial Maximum
The Last Glacial Maximum was approximately 21,000 years ago, when the most recent ice age reached its greatest intensity. Average global temperature was about 5°C lower than today.
Little Ice Age
A phase between 1550 and 1850 with globally lower temperatures and increased glaciation compared to the present.
Maar
A maar is a crater lake produced by a volcanic eruption.
Meromictic
Refers to a permanently stratified body of water, in which the bottom layer of water (the monimolimnion) does not mix with the upper layers, usually because of differences in chemical composition, such as salinity, and physical differences of temperature.
Monimolimnion
The bottom layer of a meromictic lake, which is usually anoxic or hypoxic (low in oxygen), and does not mix with the layers of water above.
Neobiota
Organisms that are non-native to the environment in which they now reside.
Neolithic
Refers to a time period beginning around 12,000 years ago with the first fixed human settlements and the domestication of animals and cereals.
Ostracod
Ostracods are tiny crustaceans that live inside a bivalved shell.
Paleolithic
Refers to a time period extending from the first use of stone tools by hominins around 3.3 million years ago to the end of the Pleistocene (the geological epoch preceding the current one, the Holocene). It is subdivided into the Lower, Middle, and Upper Palaeolithic.
Palynomorph
Palynomorphs are microfossils (between 5–500 micrometers in size) of pollen, fungal spores, or other microscopic organic matter. Their presence in sediments can be used to determine past environmental conditions.
pH
A measure of acidity or alkalinity on a logarithmic scale 0–14. pH 7 is neutral, lower values are acidic and higher values are alkali. Derived from the German Potenz (power) and the symbol H·, former chemical symbol for the hydrogen ion (now H+).
Pleistocene
The geological epoch preceding the current one (the Holocene), extending from 1.806 million years ago until around 11,000 years ago.
Polychlorinated Biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) are organic chlorine compounds that are highly toxic to humans and other animals. They have been banned in the US since 1978 and by the Stockholm Convention on Persistent Organic Pollutants in 2001. Because PCBs are non-flammable, chemically stable, and have electrical insulating properties, they were used in many products including electrical equipment, paints, plastics, pigments, and dyes.
Polycyclic Aromatic Hydrocarbons (PAHs)
Polycyclic Aromatic Hydrocarbons (PAHs) are toxic compounds commonly produced by the combustion of hydrocarbon fuels. They can be found in air, soil, and water.
Quaternary
Refers to the most recent geological period of time (the last 2 million years), which includes the Pleistocene and Holocene epochs.
Radiometric dating
Radiometric dating is a precise method of dating geological specimens by determining relative proportions of radioactive element isotopes, with known radioactive decay rates (half-lives), to thereby calculate a sample’s age. Different methods are used depending on the age of earth materials being measured. Uranium–Lead radiometric dating can provide ages for rocks back to the formation of Earth; radiocarbon dating is used to date organic remains over the last ~60,000 years.
Radionuclide
A radionuclide is a radioactive atom of an element identified by the number of nuclear neutrons and protons and energy state.
Redoxcline
A layer of water (with a strong vertical redox gradient) between the upper oxygenated and lower anoxic water.
Siliciclastic
Refers to inorganic sediments comprised of silicate minerals and rock fragments.
Spheroidal Aluminosilicates (SAPs)
A spheroid-shaped form of fly ash composed of aluminum, silicon, and oxygen, produced during high temperature oil and coal combustion.
Spheroidal Carbonaceous Particles (SCPs)
A spheroid-shaped form of black carbon particle produced during high temperature oil and coal combustion. SCPs are a distinct marker of human influence on the planet, and can now be found in environmental archives on every continent, including very remote areas such as the high Arctic and Antarctica.
Stable water isotopes
Stable isotopes are naturally-occurring, non-radiogenic isotopes of an element. Many elements have several stable isotopes. Stable water isotopes include deuterium (2H), oxygen-16, and oxygen-18, which can be used for paleoclimate reconstructions.
Suess effect
The Suess effect (named after Austrian chemist Hans Suess) refers to a change in the ratio of the atmospheric concentrations of carbon isotopes (13C and 14C) caused by fossil-fuel combustion emissions.
Technofossils
Technofossils are the material remains of human civilizations and industries that may be preserved in the geological record, including everything from stone tools to cell phones, roads and building materials.
Testate amoebae
A single-celled eukaryote with a shell-like cell wall.
Turbidites
Turbidites are sedimentary deposits caused by the disturbance of sediments on a slope by strong wave action or earthquake shock.
Unconformity
An unconformity is a break in an otherwise continuous rock record caused by a period of erosion or a pause in sediment accumulation, before the deposition of new sediments.
Varves
Annual or sub-annual layers of sediment that reflect seasonal deposition of lake sediments, recording changes in chemistry, biology, and sediment inputs and thereby providing a chronology of past environments.
X-Ray Fluorescence
X-ray fluorescence (XRF) is the emission of “secondary” (or fluorescent) X-rays from a material that has been bombarded with high-energy X-rays or gamma rays. This is used to identify component elements and their concentrations.