The abbreviation myr, "million years", is a unit of a quantity of 1,000,000 (i.e. 1×106) years, or 31.536 teraseconds.
Myr (Million years) is in common use in fields such as Earth science and cosmology. Myr is also used as with MYA ("Million Years Ago"). Together they make a reference system, one to a quantity, the other to a particular place in a year numbering system that is time before the present.
Myr is deprecated in geology, but in astronomy myr is standard. Where "myr" is seen in geology it is usually "Myr" (a unit of mega-years). In astronomy it is usually "Myr" (Million years).
In geology a debate remains open concerning the use of Myr (duration) plus Ma (million years ago) versus using only the term Ma.In either case the term Ma is used in geology literature conforming to ISO 31-1 (now ISO 80000-3) and NIST 811 recommended practices. Traditional style geology literature is written
The Cretaceous started 145 Ma and ended 66 Ma, lasting for 79 Myr.
The "ago" is implied, so that any such year number "X Ma" between 66 and 145 is "Cretaceous", for good reason. But the counter argument is that having myr for a duration and Mya for an age mixes unit systems, and tempts capitalization errors: "million" need not be capitalized, but "mega" must be; "ma" would technically imply a milliyear (a thousandth of a year, or 8 hours). On this side of the debate, one avoids myr and simply adds ago explicitly (or adds BP ), as in
The Cretaceous started 145 Ma ago and ended 66 Ma ago, lasting for 79 Ma.
In this case, "79 Ma" means only a quantity of 79 million years, without the meaning of "79 million years ago".
The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (mya). It is the third and final period of the Mesozoic Era, as well as the longest. The name is derived from the Latin creta, 'chalk'. It is usually abbreviated K, for its German translation Kreide.
The Mississippian is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier/lower of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley.
The Mesozoic Era is an interval of geological time from about. It is also called the Age of Reptiles and the Age of Conifers.
The Paleogene is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene and subsequent Neogene periods; despite no longer being recognised as a formal stratigraphic term, 'Tertiary' is still widely found in earth science literature and remains in informal use. The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. The United States Geological Survey uses the abbreviation PE for the Paleogene, but the more commonly used abbreviation is PG with the PE being used for Paleocene.
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and it began with the Cambrian Period when animals first developed hard shells preserved in the fossil record. The time before the Phanerozoic, called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
A year is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked.
Ma, MA, or master
Mya may refer to:
bya or b.y.a. is an abbreviation for "billion years ago". It is commonly used as a unit of time to denote length of time before the present in 109 years. This initialism is often used in the sciences of astronomy, geology, and paleontology.
A billion years (109 years) is a unit of time on the petasecond scale, more precisely equal to 3.16×1016 seconds.
In the geological timescale, the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma. It is preceded by the Kimmeridgian and followed by the Berriasian stage.
IEEE 1541-2002 is a standard issued in 2002 by the Institute of Electrical and Electronics Engineers (IEEE) concerning the use of prefixes for binary multiples of units of measurement related to digital electronics and computing.
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.
The term geon refers to large, geologic units of time. Geologists traditionally subdivide Earth history into a hierarchy of named intervals: eons, eras, periods, etc.. Historians subdivide the history of human activity into intervals that are comparatively much shorter. In both geological and historical scales, the divisions of equal rank are characteristically of unequal duration, and the identification of a particular interval is primarily based on its fossil, artifact, or cultural content. Both scales are calibrated against numerical ages obtained separately.
The geological history of Earth follows the major events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.
The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.
The Gallic epoch is an obsolete epoch of the Mesozoic Era's Cretaceous, the latter being a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. The Gallic epoch encompasses the Barremian, Aptian, Albian, Cenomanian and Turonian faunal stages.
The Hesperian is a geologic system and time period on the planet Mars characterized by widespread volcanic activity and catastrophic flooding that carved immense outflow channels across the surface. The Hesperian is an intermediate and transitional period of Martian history. During the Hesperian, Mars changed from the wetter and perhaps warmer world of the Noachian to the dry, cold, and dusty planet seen today. The absolute age of the Hesperian Period is uncertain. The beginning of the period followed the end of the late heavy bombardment and probably corresponds to the start of the lunar Late Imbrian period, around 3700 million years ago (Mya). The end of the Hesperian Period is much more uncertain and could range anywhere from 3200 to 2000 Mya, with 3000 Mya being frequently cited. The Hesperian Period is roughly coincident with the Earth's early Archean Eon.