The numbers and relative abundances of different genes, species, and ecosystems in a particular area. Its maintenance is important for ecological stability.
A naturally occurring community of flora and fauna (or the region occupied by such a community) adapted to the particular conditions in which they occur (e.g., tundra).
The region on land, in the oceans, and in the atmosphere that is inhabited by living organisms.
The long-term average weather for a particular region and time period. Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region. Weather describes the short-term state of the atmosphere. Climatic elements include precipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog, frost, and hail storms, and other measures of the weather.
The term "climate change" is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, "climate change" has been used synonymously with the term, "global warming". However, scientists tend to use the term in the wider sense to also include natural changes in climate.
The scientific study of climate considers not only present-day climates, their effects and their classification, but also long-term climate changes, covering both past climates (palaeoclimates) and future predictions.
The period of geological time following the Jurassic Period and preceding the Paleogene Period. Spanning 144 to 65 million years ago, it is the last period of the Mesozoic Era. Dinosaurs became extinct at the end of the Cretaceous.
Dating is the process of determining the age of geological structures, rocks, and fossils, and placing them in the context of geological time.
Absolute dating is achieved by measuring how much of a rock's radioactive elements have changed since the rock was formed using radiometric dating. Two common radiometric dating techniques are rubidium-strontium (Rb-Sr) and potassium-argon (K-Ar) methods, which have enabled scientists to establish the age of the Earth at roughly 4.5 billion years.
Relative dating can be carried out by identifying fossils of creatures that lived only at certain times, and by looking at the physical relationships of rocks to other rocks of a known age. This earliest form of dating was used prior to the discovery of radioactivity and absolute dating, and is still in use today.
From the Greek deinos, meaning "terrible", and sauros, meaning "lizard", any of a group of extinct land-based reptiles living between 205 million and 65 million years ago, during the Mesozoic Era. The reasons for their disappearance 65 million years ago are not yet fully understood.
The study of the relationship between organisms and the environments in which they live, including all living and non-living components.
An ecosystem is an integrated unit consisting of a community of living organisms -- bacteria, animals and plants -- and the physical environment -- air, soil, water, and climate -- that they inhabit. Individual organisms interact with each other and with their environment, or habitat, in a series of relationships that depends on the flow of energy and nutrients through the system.
The second epoch of the Paleogene Period, 56.5 to 35.5 million years ago, is the Eocene. Arctic climates shifted dramatically during the early to mid ages of this epoch. The name means "early recent", referring to the early forms.
The complete disappearance of a species or higher taxon. Extinctions appear when a group of animals or plants becomes unfit for survival in its natural habitat, usually to be replaced by another, better-suited animal or plant group. Survival depends largely on changes in the environment or in relationships to the other organisms in an ecosystem.
Food Web (Food Chain)
The interconnected feeding relationships in an ecosystem. A food chain consists of a sequence showing the feeding relationships between organisms in a particular ecosystem. Each organism depends on the next lowest member of the chain for its food. A pyramid schematic can be used to show the reduction in food energy at each step up the food chain.
A fossil (the word is from the Latin fossilis, meaning "dug up") is a cast, impression, or the actual remains of an animal or plant preserved in rock. Fossils were created during periods of rock formation, caused by the gradual accumulation of sediment over millions of years at the bottom of the sea bed or lake. Fossils may include footprints, an internal cast, or external impression. The study of fossils is called palaeontology. Palaeontologists are able to describe much of the geological history of a region from fossil remains.
The accumulated and incomplete totality of known fossils (dated and identified) including their placement in various rock formations and strata. Scientists refer to the fossil record to formulate hypothesis about the evolution of life on Earth. Revisions to such hypothesis occur when the (sometimes significant) gaps are narrowed by new discoveries.
Geologic Time Scale
Geological time is traditionally divided into eons, which in turn are subdivided into eras, periods, epochs and ages. The geologic time scale embraces the history of the Earth from its physical origin to the present day.
The 77th element on the periodic table of the elements, iridium is a transition metal and is one of the rarest metals on Earth. This element is, however, common in asteroids and comets, suggesting that the high concentration of iridium at the K-Pg boundary (formerly K-T boundary) is due to a catastrophic impact event.
The boundary between the rocks of the Cretaceous and Paleogene Periods, dating to 65.5 million years ago. The boundary is marked by a layer of dark clay enriched in the rare element iridium. It coincides with the end of the extinction of the dinosaurs. This suggests that the dinosaurs' extinction may have been the result of a catastrophic event involving either intense volcanism or a large meteorite impact. (The boundary was formerly known at the K-T boundary and the Cretaceous-Tertiary boundary).
An event that produces the extinction of many species at about the same time. One notable example is the boundary between the Cretaceous and Paleogene Periods (known as the K-Pg boundary) that saw the extinction of the dinosaurs and other big reptiles, and many of the marine invertebrates as well. Five known mass extinctions have taken place during Earth's history.
An era of geological time that spans 245 to 65 million years ago, before the Cenozoic Era and after the Paleozoic Era. The Mesozoic Era is subdivided into the Triassic, Jurassic and Cretaceous Periods of geological time. Dinosaurs and similar giant reptiles made their appearance during the Mesozoic and dominated most of the era.
Microfossils are so small they can only be seen with a microscope. They include fossils of pollen, bone fragments, bacteria, and the remains of microscopic marine animals and plants, such as foraminifera and diatoms.
Milankovitch Cycles (or Hypothesis)
Astronomical variations involving the earth's orbit around the sun used to explain cyclical climatic shifts (or ice ages). These variations involve changes in the Earth's tilt in a 41 000-year cycle, and wobble (called precession) on its axis in a 22 000-year cycle. Another cycle, at 92 000 years, involves the eccentricity in the Earth's orbit around the sun, changing from an elliptical to a near circular orbit -- the severest period of an ice age coinciding with the approach to circularity.
North American Cretaceous Inland Sea
Commonly known as the Western Interior Seaway, a huge shallow inland sea that divided the North American continent, from the Arctic Ocean to the Gulf of Mexico, during much of the Cretaceous Period. At its widest, it stretched between the Rocky Mountains to the West and the Appalachian Mountains to the East.
The study of ancient life, including the structure of ancient organisms and their environment, evolution, and ecology, as revealed by their fossils. Palaeontologists also use the presence of different fossils to date particular rock strata and to identify rocks that were laid down under particular conditions.
Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength. Because the radiation from the sun is relatively energetic, it has a short wavelength (ultraviolet, visible and near infrared) while energy reradiated from the Earth's surface and the atmosphere has a longer wavelength (infrared radiation) because the Earth is cooler than the sun.
Any loose material that has "settled" -- deposited from suspension in water, ice, or air, generally as the water current or wind speed decreases. Typical sediments are, in order of increasing coarseness: clay, mud, silt, sand, gravel, pebbles, cobbles and boulders.
The study of the movements of rocks on the Earth's surface. On a small-scale, tectonics involves the formation of folds and faults. On a large scale, plate tectonics deals with the movement of the Earth's surface as a whole, which can dramatically influence global climates.
The name Tertiary Period was used to refer to a span of geological time that started about 65 million years ago and ended between 3.6 and 1.8 million years ago (strong consensus is lacking). The term is no longer recommended for use in scientific contexts (Paleogene Period and Neogene Period are used instead, depending on the age). During this time, mammals took over all the ecological niches left vacant by the extinction of the dinosaurs and became the prevalent land animals.