Activity 1

Question 1

You can divide planets and moons with a solid surface into two categories:

Answer 1

1. Active surfaces
2. Inactive surfaces

Question 2

“Active” planets

Answer 2

• Have relatively “young” surfaces.
• AKA surfaces that have been recently or are currently being modified by plate tectonics, volcanic activity, active weathering/erosion and the creation of new surface materials.

Question 3

How did geologist Grove K. Gilbert oppose the beliefs that craters were purely of volcanic origin?

Answer 3

• He observed that the floors of craters on the moon were generally below the level of the surrounding plains

Question 4

Debate of circular craters with the Impact hypothesis

Answer 4

• A problem that some noted regarding the impact hypothesis was the predominantly circular shapes of most craters
• Argued that only impacts striking the ground directly from overhead (at a 90° angle to the ground’s surface) should result in circular craters.
• Since most impacts occur at an angle to the ground surface, it was argued that most craters formed this way should be elliptical, not circular.

Question 5

Debate of circular craters with the Impact hypothesis - CONSIDERATION OF SPEED:

Answer 5

• Did not consider the speeds most impacting bodies travel—between 17 and 70 kilometres per second
• Before impact, the meteor possesses much kinetic energy. But upon impact, is converted into other forms, including heat.
• All matter is held together by binding energy, which physically holds the atoms and molecules together.
• If the energy produced during the impact exceeds the binding forces that hold the meteor together, it will explode in all directions, generating a spherical shockwave and heat and ultimately creating a circular crater.
• Throughout this process, most impacting bodies are vaporized and/or fragmented.
• Materials are ejected from the crater, but most fall back to cover the crater floor

Question 6

Simple Impact Craters

Crater Types and Features

Answer 6

• Most common
• Characterized by bowl-like shape with a raised outer rim.
• When a meteor strikes the surface, it creates a cavity with a circular, raised rim and a flat or slightly curved floor
• Rim height and diameter depend on the size and velocity of the impacting object.
• Floor - smooth with minor variations due to the ejection of material during the impact.

Question 7

Complex Impact Craters

Crater Types and Features

Answer 7

• Larger and more intricate in structure than simple craters
• Form when a significantly larger object strikes the surface with greater force, causing extensive surface deformation.
• Have a central peak or peaks surrounded by a ring or rings of elevated terraces (from rebound of material); terraces result from the collapse of the crater walls inward

Question 8

Materials Ejected from Craters

Crater Types and Features

Answer 8

• Additional common features are rays caused by ejected material (ejecta) exiting the crater during the impact
• **”Lobes” **of materials that are thought to form when ice in the subsurface melted during the impact, causing a slurry of materials to flow over the surface.

Question 9

Age Relationships - how can we tell which craters are older/younger?

Answer 9

• Cross-cutting relationships