Geologic time scale

The geological time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history. The table of geologic time spans presented here agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy.

Evidence from radiometric dating indicates that Earth is about 4.54 billion years old. The geology or deep time of Earth’s past has been organized into various units according to events which took place in each period. Different spans of time on the GTS are usually delimited by changes in the composition of strata which correspond to them, indicating major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous–Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other groups of life. Older time spans which predate the reliable fossil record (before the Proterozoic Eon) are defined by the absolute age.

Age (genus)

Age is a genus of moths belonging to the subfamily Olethreutinae of the family Tortricidae.

Species

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Âge

Âge (アージュ, Āju) is a division of Acid Co., Ltd., a Japanese publisher of adult video games and visual novels. Âge was formerly known as Relic and developed video games for consoles. It gained fame following the release of its 2001 adult visual novel Kimi ga Nozomu Eien. It was founded by Hirohiko Yoshida, Baka Prince Persia, Nanpuureima, Spin Drill, and Carnelian. Âge games are published under the brands Âge, Mirage, and Φâge.

List of developed games

References

External links

Age (journal)

Age is a scientific journal focused on the biology of aging and research on biomedical applications that impact aging. This includes evolutionary biology, biophysics, genetics, genomics, proteomics, molecular biology, cell biology, biochemistry, endocrinology, immunology, physiology, pharmacology, neuroscience, and psychology. It is an international peer-reviewed monthly and the official journal of the American Aging Society. It is published by Springer Science+Business Media, and the editor-in-Chief is Donald K. Ingram. According to the 2012 Journal Citation Reports, its impact factor is 4.084.

External links

Period (gene)

Period (per) is a gene located on the X chromosome of Drosophila melanogaster. Oscillations in levels of both per transcript and its corresponding protein PER have a period of approximately 24 hours and together play a central role in the molecular mechanism of the Drosophila biological clock driving circadian rhythms in eclosion and locomotor activity. Mutations in the per gene can shorten (per^S), lengthen (per^L), and even abolish (per⁰) the period of the circadian rhythm.

Discovery

The period gene and three mutants (per^S, per^L, and per⁰) were isolated in an EMS mutagenesis screen by Ronald Konopka and Seymour Benzer in 1971. The per^S, per^L, and per⁰ mutations were found to complement each other, so it was concluded that the three phenotypes were due to mutations in the same gene. The discovery of mutants that altered the period of circadian rhythms in eclosion and locomotor activity (per^S and per^L) indicated the role of the per gene in the clock itself and not an output pathway. The period gene was first sequenced in 1984 by Michael Rosbash and colleagues. In 1998, it was discovered that per produces two transcripts (differing only by the alternative splicing of a single untranslated intron) which both encode the PER protein.

Period (geology)

A geologic period is one of several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.

These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history.

Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages.

Structure

The twelve currently recognised periods of the present eon – the Phanerozoic – are defined by the International Commission on Stratigraphy (ICS) by reference to the stratigraphy at particular locations around the world.

In 2004 the Ediacaran Period of the latest Precambrian was defined in similar fashion (and was the first such newly designated period in 130 years) but earlier periods are simply defined by age.

A consequence of this approach to the Phanerozoic periods is that the ages of their beginnings and ends can change from time to time as the absolute age of the chosen rock sequences, which define them, is more precisely determined.

Periodic function

In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of 2π radians. Periodic functions are used throughout science to describe oscillations, waves, and other phenomena that exhibit periodicity. Any function which is not periodic is called aperiodic.

Definition

A function f is said to be periodic with period P (P being a nonzero constant) if we have

for all values of x in the domain. If there exists a least positive constant P with this property, it is called the fundamental period (also primitive period, basic period, or prime period.) A function with period P will repeat on intervals of length P, and these intervals are referred to as periods.

Geometrically, a periodic function can be defined as a function whose graph exhibits translational symmetry. Specifically, a function f is periodic with period P if the graph of f is invariant under translation in the x-direction by a distance of P. This definition of periodic can be extended to other geometric shapes and patterns, such as periodic tessellations of the plane.