I. The Highlands  Surface feature that is light in color, high in elevation (mountainous), and heavily cratered

Rocks of the Highlands  Anorthosite – a single mineral rock composed of plagioclase feldspar. It crystallizes as magma cools and floats to the surface. This suggests that the Moon was completely surrounded by a huge ocean of magma soon after it formed.

Earthly Plagioclase Feldspar (Mineral)

Rocks of the Highlands con’t  Breccia – is a collection of rock fragments all mixed together that probably resulted from the violent impacts of meteors.

Earthly Breccia Sedimentary Rock

II. Maria  Surface feature that is dark in color, low in elevation, and smooth.

Rocks of the Maria  Basalt – a type of volcanic rock that contains the mineral pyroxene and has holes called “vesicles” that are frozen gas pockets.

Earthly Basalt (Igneous Rock)

Rocks of the Maria con’t  Orange soil – formed from “fire fountaining.” Composed of glassy pieces (small drops of lava that did not have time to cool) and dark, opaque pieces (partial crystallization of the mineral ilmentite)

Question:  There is no orange soil on the Earth. However the orange soil on the Moon matches the composition of some soils on Earth. How can this be?? VIDEO: Apollo 17 astronaut reacts to orange soil

Answer:  The Moon does not have an atmosphere, so the iron (orange) does not react with oxygen! Fantastic sports fans!

III. Craters  Crater – a large, bowl-shaped feature on the surface typically caused by an impact of a meteorite. Crater formation

IV. Rilles  Rilles – a river-like feature (lava channel)

V. Nearside vs. Farside  The Moon revolves around the Earth at the same rate in which is rotates (27.3 days). Therefore it is said to have a synchronous orbit around the Earth resulting in the same side (nearside) facing the Earth at all times. Animation: Synchronous Orbit

 The Moon revolves around the Earth at the same rate in which is rotates (27.3 days). Therefore it is said to have a synchronous orbit around the Earth resulting in the same side (nearside) facing the Earth at all times.

NearsideFarside Highlands and Maria Mostly Highlands More rilles/lava flows More craters

VI. Relative Age Dating  Astronomers can determine which surface features on the Moon are older than others to understand its geologic history.

Examples  Small craters located within a larger one indicates that the larger one was there first.

Examples con’t  The highlands are heavily cratered compared to the mare regions. This indicates that the highlands are older and that the lava flows are more recent.

Examples con’t  Craters with smooth bottoms indicate that they existed before the lava flow occurred.

Relative ages of lunar features in the vicinity of the crater Copernicus are indicated by superposition of ejecta and mare basalts. Ejecta from Copernicus are superposed on all other features and are therefore the youngest materials. Ejecta from Eratosthenes (northeast of Copernicus) rest on the mare basalts and are younger than the mare material but older than Copernicus. Ejecta from the Imbrium Basin are covered partly by mare lavas and rest on the densely cratered highlands. Thus the basin and the lava flows are younger than the complex ejecta deposits of the highlands.