Why is radiometric dating important

The alkali suite consists of alkali anorthosites with relatively sodic plagioclase (An70-85), norites (plagioclase-orthopyroxene), and gabbronorites (plagioclase-clinopyroxene-orthopyroxene) with similar plagioclase compositions and mafic minerals more iron-rich than the magnesian suite.

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These rocks apparently form by the extreme fractional crystallization of magnesian suite or alkali suite magmas, although liquid immiscibility may also play a role.

U-Pb date of zircons from these rocks and from lunar soils have ages of 4.1-4.4 Ga, more or less the same as the magnesian suite and alkali suite rocks. O'Keefe and others linked lunar granites with tektites found on Earth although many researchers refuted these claims.

Moon rocks on Earth come from three sources: those collected by the US Apollo manned lunar landings from 1969 to 1972; samples returned by three Soviet Luna unmanned probes in the 1970s; and rocks that were ejected naturally from the lunar surface by cratering events and subsequently fell to Earth as lunar meteorites.

During the six Apollo landing missions, 2,415 samples weighing 380.96 kilograms (839.87 lb) were collected.

The magnesian suite (or "mg suite") consists of dunites (90% olivine), troctolites (olivine-plagioclase), and gabbros (plagioclase-pyroxene) with relatively high Mg/Fe ratios in the mafic minerals and a range of plagioclase compositions that are still generally calcic (An86-93).

These rocks represent later intrusions into the highlands crust (ferroan anorthosite) at round 4.3-4.1 Ga.They consist of quartz, plagioclase, orthoclase or alkali feldspar, rare mafics (pyroxene), and rare zircon.The alkali feldspar may have unusual compositions unlike any terrestrial feldspar, and they are often Ba-rich.In some regards, lunar rocks are closely related to Earth's rocks in their isotopic composition of the element oxygen.The Apollo moon rocks were collected using a variety of tools, including hammers, rakes, scoops, tongs, and core tubes.In contrast to the Earth, large portions of the lunar crust appear to be composed of rocks with high concentrations of the mineral anorthite. Furthermore, some of the mare basalts have very high levels of titanium (in the form of ilmenite).

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