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Chapter 9: Problem 26

Suppose we were to make the following discoveries. (These are not real discoveries.) In light of your understanding of planetary geology, decide whether the discovery should be considered reasonable or surprising. (In some cases, both views can be defended.) Explain your answer, if possible tracing your logic back to the terrestrial worlds' fundamental properties of size, distance from the Sun, and rotation rate. Clear-cutting in the Amazon rain forest on Earth exposes vast regions of ancient terrain that is as heavily cratered as the lunar highlands.

Short Answer

Expert verified
Given Earth's active geology, the discovered cratering would be surprising.

Step by step solution

01

Assess Historical Cratering Activity

The Earth, as a terrestrial planet, has been exposed to meteoritic impacts like the Moon and other planets. However, most of Earth鈥檚 surface is not heavily cratered. We need to understand the removal of ancient craters over Earth's geologic history.
02

Evaluate Geological Processes

On Earth, active geological processes such as volcanic activity, plate tectonics, erosion, and sedimentation constantly renew the surface. These processes are responsible for erasing craters over time, unlike the relatively static surface of the Moon.
03

Relate to Terrestrial World Properties

Earth's size and geological activity contribute to the renewal of its surface. In contrast, the smaller size and lack of geological activity on the Moon allow craters to remain visible over billions of years.
04

Consider Historical and Regional Geology

Ancient terrains could potentially retain some craters if they are geologically stable regions with minimal changes. However, on Earth, such regions are rare due to active processes.
05

Analyze Probability of the Discovery

Given Earth's active geology and minimally cratered current appearance, the discovery of lunar-like cratering in the Amazon would seem surprising. Most ancient terrains known are less cratered due to Earth's processes.

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Key Concepts

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

Cratering Activity
Cratering activity is a fascinating concept in planetary geology that reveals much about a planet's history. When celestial bodies impact a planet鈥檚 surface, they create craters. This happens not only on Earth but on many other planetary bodies too. Yet, Earth鈥檚 surface appears quite different from, say, the Moon鈥檚 heavily cratered face. The reason lies in Earth's dynamic nature.

  • Earth is continuously exposed to meteoritic impacts, just like the Moon.
  • However, unlike the Moon, Earth has mechanisms that can erase or hide these craters over time.
The Moon lacks these processes, allowing impacts to leave permanent marks. This makes the discovery of lunar-like cratering on Earth, such as in the Amazon rain forest, seem surprising because it contradicts the usual geological transformation we see on Earth.
Geological Processes
Geological processes play a crucial role in shaping a planet's surface. On Earth, several active processes constantly work to renew the surface, which is why we see fewer ancient craters compared to the Moon. These processes include:

  • Volcanic Activity: Eruptions can deposit new material on the surface, covering older features like craters.
  • Plate Tectonics: The movement of Earth's plates can recycle surface material, creating mountains and ocean trenches.
  • Erosion: Wind, water, and ice wear down landforms and redistribute materials.
  • Sedimentation: Layers of sediments can cover older geological features.
These processes are less active on the Moon, where the surface remains largely unaltered by such dynamics. This makes Earth鈥檚 geology unique and complex compared to other terrestrial worlds.
Earth Surface Renewal
Earth's ability to continuously renew its surface sets it apart from other planetary bodies. The Earth鈥檚 surface renewal is a constant process driven by internal and external forces. These renewal forces include geological processes such as tectonic activities and weathering.

  • Internal Forces: These come from deep within the Earth, such as heat from the core driving mantle convection, leading to tectonic shifts.
  • External Forces: Weather patterns and climatic conditions contribute to erosion and sedimentation.
This constant renewal ensures that ancient landscapes are rarely exposed for long. It explains why discovering heavily cratered ancient terrain on Earth is unusual, as such features have typically been erased or covered over time.
Terrestrial World Properties
The terrestrial worlds, including Mercury, Venus, Earth, and Mars, share many fundamental properties, yet have distinct geological features due to differences in size, distance from the Sun, and rotation rates. These properties influence how each planet鈥檚 surface evolves.

  • Size: A larger size often means more gravitational pull and a higher chance of retaining an atmosphere, which can lead to dynamic surface weathering and tectonic activity.
  • Distance from the Sun: This affects surface temperatures, atmospheric composition, and weather patterns, influencing geological processes.
  • Rotation Rate: Faster rotation can influence atmospheric patterns and even impact geological activity to some extent.
Earth鈥檚 size and active geological processes help renew its surface. Meanwhile, smaller bodies like the Moon and Mercury show a different history of impact because of their size and lack of geological activity. Understanding these properties helps explain the variability in planetary surfaces across the terrestrial worlds.

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Most popular questions from this chapter

Be sure to show all calculations clearly and state your final answers in complete sentences. Doubling Your Size. Just as the surface area-to-volume ratio depends on size, so can other properties. To see how, suppose that your size suddenly doubled- that is, your height, width, and depth all doubled. (For example, if you were 5 feet tall before, you now are 10 feet tall. a. By what factor has your waist size increased? b. How much more material will be required for your clothes? (Hint: Clothes cover the surface area of your body.) \(c .\) By what factor has your weight increased? (Hint: Weight depends on the volume of your body.) d. The pressure on your weight-bearing joints depends on how much weight is supported by the surface area of each joint. How has this pressure changed?

Mystery Planet. It's the year 2098 , and you are designing a robotic mission to a newly discovered planet around a nearby star that is nearly identical to our Sun. The planet is as large in radius as Venus, rotates with the same daily period as Mars, and lies \(1.2 \mathrm{AU}\) from its star. Your spacecraft will orbit but not land on the planet. a. Some of your colleagues believe that the planet has no metallic core. How could you support or refute their hypothesis? b. Other colleagues suspect that the planet has no atmosphere, but the instruments designed to study the planet's atmosphere fail because of a software error. However, the spacecraft can still photograph geological features. How could you use the spacecraft's photos of geological features to determine whether a significant atmosphere is (or was) present on this planet?

Suppose we were to make the following discoveries. (These are not real discoveries.) In light of your understanding of planetary geology, decide whether the discovery should be considered reasonable or surprising. (In some cases, both views can be defended.) Explain your answer, if possible tracing your logic back to the terrestrial worlds' fundamental properties of size, distance from the Sun, and rotation rate. We find a planet in another solar system that is as large as Earth but as heavily cratered as the Moon.

"Coolest" Surface Photo. Visit the Astronomy Picture of the Day Web site, and search for past images of the terrestrial worlds. Look at many of them, and choose the one you think is the "coolest." Write a short description of what it shows, and explain what you like about it.

Suppose we were to make the following discoveries. (These are not real discoveries.) In light of your understanding of planetary geology, decide whether the discovery should be considered reasonable or surprising. (In some cases, both views can be defended.) Explain your answer, if possible tracing your logic back to the terrestrial worlds' fundamental properties of size, distance from the Sun, and rotation rate. We find a planet in another solar system with Earth-like seafloor crust and continental crust but that apparently lacks plate tectonics or any other kind of crustal motion.
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