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Rocks found on the Moon are between \(3.1\) and \(4.47\) billion years old. By contrast, the majority of the Earth's surface is made of oceanic crust that is less than 200 million years old, and the very oldest Earth rocks are about 4 billion years old. If the Earth and Moon are essentially the same age, why is there such a disparity in the ages of rocks on the two worlds?

Short Answer

Expert verified
The difference in the ages of rocks on Earth and Moon, despite the two bodies being of similar age, is primarily because of Earth's active geological processes including plate tectonics, erosion and weathering, which continuously create and wear away rocks. In contrast, the moon does not have these processes and hence has preserved its older rocks.

Step by step solution

01

Understand the Geological Ages of Rocks

The moon has rocks between 3.1 to 4.47 billion years old. The rocks on Earth, however, are mainly less than 200 million years with the oldest being about 4 billion years old. These ages provide a period within which the respective celestial bodies have preserved their geological history.
02

Understand the Geological Processes on Earth and Moon

Geological processes on Earth like plate tectonics cause a continuous remodeling of the Earth's surface. These processes lead to the formation of newer rocks at the expense of older ones. Processes such as erosion and weathering also contribute to wearing away the rocks. The moon doesn't have these processes, thereby preserving its old rocks.
03

Contrast the Geological Processes

On Earth, the geologically active nature results in constant creation and destruction of rocks which leads to younger average rock age. However, the Moon's geologically inactive nature with no atmosphere, weathering or recent volcanic activity, allows it to preserve its ancient rocks. Therefore, even though both bodies are similar ages, their rock ages differ due to the geological activities (or lack thereof) on their surfaces

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lunar Geology
A fascinating aspect of lunar geology is how well it preserves the Moon's history. Unlike Earth, the Moon lacks an atmosphere and the geological activity that reshapes our planet's surface. Lunar rocks, aging between 3.1 and 4.47 billion years old, act as time capsules, enabling scientists to glimpse the solar system's early history.

Due to the absence of plate tectonics and weathering processes on the Moon, the impact craters and mare basalts formed billions of years ago remain relatively unchanged. This static preservation is starkly different from Earth, where geological activities such as earthquakes and volcanoes constantly create, alter, and recycle rock material. The older surfaces on the Moon, therefore, offer us a window into the past, untouched by the processes that tend to erase or bury evidence on Earth.
Plate Tectonics
Plate tectonics is the driver behind Earth's dynamic surface. It describes the continuous movement of Earth's lithospheric plates over the malleable asthenosphere. This theory explains the creation of new crust at divergent boundaries where plates pull apart, like the mid-ocean ridges, and the destruction of older crust at convergent boundaries where one plate subducts beneath another.

These plate movements are responsible for the dramatic reshaping of our planet's surface over millions of years, leading to the formation of mountain ranges, deep-sea trenches, and frequent volcanic and seismic activities. The constant recycling of Earth's surface due to plate tectonics results in a much younger geological profile when compared to the Moon.
Earth's Geological Processes
Earth's geological processes are numerous and can be extremely powerful. Erosion, caused by water, wind, and ice, wears away rocks and soil, continually reshaping the landscape. Weathering breaks down rocks both chemically and physically. Furthermore, volcanic activity adds new rock to the surface, both on land and under the oceans, contributing to the creation of new crust.

These processes, together with plate tectonics, mean that Earth's surface is constantly being recycled. As new rock forms, old rock is pushed beneath the plates and re-melted into the mantle. This cycle explains why Earth, despite being nearly as old as the Moon, has much younger surface rocks. The oldest rocks on Earth, at about 4 billion years old, are vastly outnumbered by those formed more recently due to the planet's vigorous geological activity.

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Most popular questions from this chapter

The youngest lunar anorthosites are \(4.0\) billion years old, and the youngest mare basalts are \(3.1\) billion years old. Would you expect to find any impact breccias on the Moon that formed less than \(3.1\) billion years ago? Explain your answer.

Temperature variations between day and night are much more severe on the Moon than on Earth. Explain why.

Describe the differences between the maria and the lunar highlands. Which kind of terrain covers more of the Moon's surface? Which kind of terrain is more heavily cratered? Which kind of terrain was formed later in the Moon's history? How do we know?

Why are there no sedimentary rocks on the Moon?

Use the Starry Night Enthusiast \({ }^{\mathrm{TM}}\) program to observe the apparent change in size of the Moon as seen from the surface of the Earth. Click the Home button in the toolbar. Stop the time flow by clicking the Stop time button (the button with a square icon in the Time Flow Rate section of the toolbar). Click each field of the Time and Date display pane in the toolbar and use the keyboard to set the time to \(12: 00: 00 \mathrm{~A} . \mathrm{M}\). and the date to \(\mathrm{O}\) tober 16,2006 . You can now set up the view of the Moon as if you were observing from a transparent Earth in continuous darkness. Open the Options pane by clicking its tab on the left border of the view window. In the Local View layer of the Options pane, uncheck the boxes beside the Daylight and Local Horizon options. Open the Find pane and click the menu button at the left of the entry for the Moon and select Magnify from the menu to display a stationary image of the magnified Moon in the center of the view. Notice the Moon's phase. (a) Select Options > Solar System > PlanetsMoons... from the menu. In the Planets-Moons dialog box, click the slide control next to the Show dark side label near the top of the window and adjust the control all the way to the right (Brighter) side of the scale. Then click the OK button to close the dialog box. Note that the image of the Moon now appears full because Starry Night Enthusiast TM has artificially brightened the dark side of the image of the Moon, effectively removing the appearance of the Moon's phases. (b) Use the + button in the Zoom section of the toolbar to adjust the field of view to about \(55^{\prime} \times 45^{\prime}\). Starry Night Enthusiast \({ }^{\mathrm{TM}}\) can display a reference field of view (FOV) upon this sky. Open the FOV pane by clicking its tab. Select the 30 Arcminutes option. Then click the FOV tab to close the pane. (c) The final view is of the Moon, its dark side artificially brightened, as it would be seen from your home location if the Earth were airless and transparent, surrounded by a yellow FOV circle 30 arcminutes in diameter. Note the size of the Moon relative to this reference circle. Set the Time Flow Rate in the toolbar to 1 minute. Run Time Forward for least 24 hours and observe the apparent size of the Moon relative to the reference circle. (c) Note that the apparent size of the Moon changes somewhat over the course of a day (of simulated time). Explain in terms of the Earth's rotation. (Hint: In this view, Starry Night Enthusiast \({ }^{\text {Tm }}\) has made the Earth transparent, so you can see objects that would normally be below the horizon. As the Earth rotates, your observing location on the surface is carried along and your distance from the Moon changes.) (d) Change the Time Flow Rate to 1 day and again click the Run Time Forward button. Does the apparent size of the Moon always stay the same, or does it vary? Explain what this tells you about the shape of the Moon's orbit.

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