Related Words

Epoch: Subdivision of a geological period.

National Tidal Datum Epoch: The specific l9-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values (e.g., mean lower low . . . View Full Definition

Prenatal Epoch: The astrological moment of conception. According to Ptolemy, the natal Ascendant or Descendant coincides with the Moon's zodiacal position at the prenatal epoch, ten lunar months prior to bi . . . View Full Definition

Polarity Epoch: An interval of time between reversals of Earth's magnetic field.

National Tidal Datum Convention: Effective November 28, 1980, the Convention: (1) establishes one uniform, continuous tidal datum system for all marine waters of the United States, its territories, Commonwealth of Puerto Ri . . . View Full Definition

Mean Sea Level (MSL): A tidal datum. The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specified in the name; e.g., monthly mean sea level and yearly mean sea level.

Mean River Level: A tidal datum. The average height of the surface of a tidal river at any point for all stages of the tide observed over the National Tidal Datum Epoch. It is usually determined from hourly h . . . View Full Definition

Magnetic Reversal: A change in the polarity of Earth's magnetic field in which the north magnetic pole becomes the south magnetic pole and vice versa. Also known as geomagnetic reversal or polarity reversal. E . . . View Full Definition

Time Scale: The division of geologic history into eras, periods, and epochs accomplished through stratigraphy and paleontology.

Polarity Reversal: A change in the polarity of Earth's magnetic field in which the north magnetic pole becomes the south magnetic pole and vice versa. Also known as geomagnetic reversal or magnetic reversal. E . . . View Full Definition