tar/oil sands
Sand or clay formations that contain a heavy-density crude oil (crude bitumen); extracted by surface mining. (Chapter 19)
tax credit
A reduction in the tax one has to pay in exchange for some desirable action. (Chapter 20)
terracing
On steep slopes, land is leveled into steps; reduces soil erosion and runoff down the hillside. (Chapter 17)
tertiary sources
Sources that present and interpret information from secondary sources. (Chapter 3)
testable
Having a possible explanation that generates predictions for which empirical evidence can be collected to verify or refute the hypothesis. (Chapter 2)
test group
The group in an experimental study that is manipulated such that it differs from the control group in only one way. (Chapter 2)
theory
A widely accepted explanation of a natural phenomenon that has been extensively and rigorously tested scientifically. (Chapter 2)
threatened
Describes a species that is at risk for extinction. (Chapter 11)
threatened species
Species that are at risk for extinction; various threat levels have been identified, ranging from “least concern” to “extinct.” (Chapter 13)
tight oil
Light (low density) oil in shale rock deposits of very low permeability; extracted by fracking. (Chapter 19)
time delay
Actions that produce a benefit today and set into motion events that cause problems later on. (Chapter 1)
top-down regulation
The control of population size by factors that reduce population size (resistance factors) such as predation, competition, or disease. (Chapter 9)
total fertility rate (TFR)
The number of children the average woman has in her lifetime. (Chapter 4)
toxic substances/toxics
Chemicals that cause damage to living organisms through immediate or long-term exposure. (Chapter 3)
toxicologist
A scientist who studies the specific properties of potentially toxic substances. (Chapter 3)
trade-offs
The imperfect and sometimes problematic responses that we must at times choose between when addressing complex problems. (Chapter 1)
tragedy of the commons
The tendency of an individual to abuse commonly held resources in order to maximize his or her own personal interest. (Chapter 1)
transboundary problem
A problem that extends across state and national boundaries; pollution that is produced in one area but falls in or reaches other states or nations. (Chapter 20, 24)
transgenic organism
An organism that contains genes from another species. (Chapter 16)
transpiration
The loss of water vapor from plants. (Chapter 14)
triple bottom line
The combination of the environmental, social, and economic impacts of our choices. (Chapter 1, 6)
trophic levels
Feeding levels in a food chain. (Chapter 10)
troposphere
The region of the atmosphere that starts at ground level and extends upward about 7 miles. (Chapter 2)
true cost
The sum of both external and internal costs of a good or service. (Chapter 6)