Geology - Our Solar System - Quick Guides

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Study GuideGeology–Our Solar System1. Earth’s MoonScientists have learned a lot about Earth’s Moon through many years of study. They have usedpowerful telescopes and information from both uncrewed spacecraft and crewed missions. Each ofthese methods has helped us better understand what the Moon is like on the surface and deep inside.1.1 Studying the Moon’s InteriorWhen astronauts visited the Moon, they left behind special instruments calledseismic detectors.These tools measure vibrations inside the Moon. Today, they record about400 small moonquakesevery year.Most scientists believe these moonquakes happen because ofEarth’s gravity. As Earth pulls on theMoon, it causes tiny movements along cracks, or faults, in theMoon’s crust.1.2 Layers Inside the MoonSeismic data show that the Moon has alayered interior, much like Earth.•Theouter crustis about65 kilometers thick.•This crust is made mainly ofbasaltandfeldspar-rich rock.•Beneath the crust, scientists believe there is amantle, even though it cannot be directlyobserved.

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Study GuideCalculations also show that the Moon issolid down to about 1,000 kilometers. This depth marksthe lower boundary of the Moon’slithosphere, which includes the crust and the rigid upper part of themantle.1.3 Features on the Moon’s SurfaceThe Moon’s surface shows clear differences between regions:•Thelarge, smooth lowlandsare covered bybasaltic lava flows, formed when molten rockonce spread across the surface.•Themountainous regionsare higher and rougher.Geophysical measurements suggest that these mountainous areas areisostatically balanced. Thismeans that long ago, the Moon’s lithosphere was soft enough to allow thicker crustal regions to“float,” much like ice floating on water.1.4 Moon Rocks and Their AgeAstronauts also brought backrock samplesfrom the Moon. These rocks include:•Anorthosite, a feldspar-rich igneous rock commonly found in the Moon’s crust•Basalt, which formed from cooled lava flowsScientists have dated these rocks and found that they arebetween 3.0 and 4.5 billion years old.The oldest of these rocks likely formed around thebeginning of the solar system.2. Mars2.1 Mars and Earth: What’s Similar and What’sDifferentMars shares several features with Earth, which is why it fascinates scientists. A day on Mars lastsalmost 24 hours, very close to an Earth day. Mars also has an atmosphere, polar ice caps mademainly of carbon dioxide, and experiences seasons like winterand summer.However, there are important differences too. Unlike Earth,Marsdoes not have a strong, dipolarmagnetic field. This means it is less protected from solar radiation. So far, scientists have not foundany direct evidence of life on Mars, although research is still ongoing.

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Study Guide2.2 Volcanoes and Landscapes of the Northern HemisphereThe northern hemisphere of Mars is famous for its massive volcanoes. This region contains largeshield volcanoes and many volcanic cones, with impactcraters spread far apart.Some of these volcanoes are enormous—up to three times taller than the tallest volcanic mountainson Earth. The most impressive of all isOlympus Mons, the largest volcanic structure ever discoveredin the solar system.The huge size of these volcanoes tells scientists two important things:•Magma must have flowed to the surface for a very long time.•The Martian lithosphere (the rigid outer layer of the planet) is extremely strong.Scientists have also identifiedhorst and grabenfault basins, which form when the planet’s cruststretches and breaks. Many volcanic cones show very little damage from meteor impacts. Thissuggests the volcanic activity is relatively recent. In fact, the newest lava flows may be less than100million years old, based on the low number of craters on their surfaces.2.3 The Cratered Southern HemisphereThe southern hemisphere looks very different. Instead of volcanoes, it is covered with thousands ofimpact craters. This heavy cratering shows that the surface is much older and that volcanic activitythere has been far less intense compared to the north.2.4 Surface Materials, Wind, and Signs of WaterThe Martian surface is heavily weathered and made mostly of clay and sulfate materials. Strongwinds shape this loose material into large sand dunes, which are common across the planet.Mars also shows features that look like winding, braided channels. These resemble river systems onEarth and suggest that running water—or even massive floods—once shaped the surface.Scientists think flooding could have happened if:•Frozen ground suddenly melted due to volcanic (magmatic) heat, or•A major change in climate caused ice to thaw quickly.

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