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Apsidal precession combines with the 25,700-year cycle of axial precession (see above) to vary the position in the year that the Earth reaches perihelion. Apsidal precession shortens this period to about 21,000 years, at present.
The tilt of the Earth's polar axis remains constant but describes a circular path in space during a period known as The Great Year. The term Great Year has more than one major meaning. It is defined by scientific astronomy as "The period of one complete cycle of the equinoxes around the ecliptic, or about 25,800 years".
The coincidence of the annual cycles of the apses (closest and further approach to the Sun) and calendar dates (with seasons noted) at four equally spaced stages of a fictitious precessionary cycle of 20,000 years (rather than the Earth's true precessionary cycle of 26,000 years). The season dates are those in the north.
c. 4,500 Ma – Sun enters main sequence: a solar wind sweeps the Earth-Moon system clear of debris (mainly dust and gas). End of the Early Bombardment Phase. Basin Groups Era begins on Earth. c. 4,450 Ma – 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiates from lower magmas. The ...
The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of the Earth's crust and the Earth itself.
This is an accepted version of this page This is the latest accepted revision, reviewed on 16 February 2025. Scientific projections regarding the far future Several terms redirect here. For other uses, see List of numbers and List of years. Artist's concept of the Earth 5–7.5 billion years from now, when the Sun has become a red giant While the future cannot be predicted with certainty ...
Relationship of Earth's orbit to periods of glaciation. Firstly, changes in the orbital eccentricity of Earth occur on a cycle of about 100,000 years. [11] Secondly, the inclination or tilt of Earth's axis varies between 22° and 24.5° in a cycle 41,000 years long. [11]
See calendar and list of calendars for other groupings of years. See history, history by period, and periodization for different organizations of historical events. For earlier time periods, see Timeline of the Big Bang, Geologic time scale, Timeline of evolution, and Logarithmic timeline