Knowra Eratosthenian Eratosthenian The Eratosthenian is a period in lunar history, roughly 3.2 to 1.1 billion years ago, marked by declining impact cratering and widespread mare volcanism.
Lunar mare : A broad, dark basalt plain on the Moon, formed when lava filled an impact basin or depression. Mare basalts record the volcanism that continued through much of this period.
Lunar geologic timescale : A division of lunar history into periods based on stratigraphy, impact-crater density, and radiometric ages. It places the Eratosthenian between the Imbrian and Copernican periods.
Copernicus crater : A prominent impact crater in the Moon’s Oceanus Procellarum region, about 93 kilometers across. Its rays and ejecta make it a classic example of a younger Copernican crater over older terrain.
William Kenneth Hartmann : An American planetary scientist whose work helped develop modern models of lunar impact history and planetary accretion. His work contributed to the crater chronology used to interpret lunar surfaces.
Lunar basalt : Basaltic rock erupted onto the lunar surface, composed mainly of pyroxene, plagioclase, and ilmenite. Its composition and ages constrain the scale and timing of Eratosthenian eruptions.
Imbrian : A lunar geologic period preceding the Eratosthenian, marked by major basin formation and extensive mare volcanism. Its older surfaces generally preserve more basin-forming impacts and intense early volcanism.
Tycho crater : A young, roughly 85-kilometer lunar impact crater in the southern highlands, with conspicuous rays. Its bright ray system contrasts with the subdued appearance of much older Eratosthenian surfaces.
Gerard Kuiper : A Dutch-American astronomer who founded the Lunar and Planetary Laboratory and advanced telescopic and spacecraft-based lunar studies. His mapping efforts helped establish the stratigraphic framework for lunar periods.
Lunar volcanism : The eruption and emplacement of molten rock on the Moon, chiefly as basaltic lava and volcanic deposits. Eratosthenian mare activity was one phase of the Moon’s longer volcanic history.
Copernican : The youngest lunar geologic period, beginning about 1.1 billion years ago and continuing to the present. Its fresher craters and ejecta distinguish it from older Eratosthenian terrain.
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