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Terrestrial World Surfaces

Solid rocky surfaces shaped (to varying degrees) by: Impact cratering

Volcanism

Tectonics (gross movement of surface by interior forces)

Erosion (by impacts or by weather)

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The Earth's Surface

Unlike Mercury and the Moon, impact craters are few and far between on the Earth.

From a crater counting perspective the surface is “young”

The Earth has been impacted as frequently, if not more frequently than the Moon, yet those scars have been erased

Note that the Earth's atmosphere offers little protection against the large impactors that produce the craters seen above.

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The Earth's Surface

The Earth's larger size means that it is still geologically active.

New surface is being created and old surfaces are being resurfaced regularly.

The Earth also retains an atmosphere which makes for efficient erosion of craters.

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Geological Activity vs. Planetary Size

It's no coincidence that the smallest worlds above are the ones that are heavily cratered.

The larger a world is the more readily it retains its internal heat. A pea cools off much more quickly than a potato

Earth and Venus are still hot in the interior and molten material can reach and re-surface the surface.

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How Lightly Cratered?

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How Lightly Cratered?

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Two Distinct Terrains: Continents and Basins The Earth has two distinct surface levels

Continents: Thick portions of the crust that occupy high elevations

Basins: Thiner crust occupying the “lowlands”

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Two Distinct Terrains: Continents and Basins Interestingly, there is just enough water on Earth to fill the basins.

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Two Distinct Terrains: Continents and Basins Interestingly, there is just enough water on Earth to fill the basins. It didn't have to be this way, consider Jupiter's moon Europa

The world is submerged under a 60 mile deep ocean frozen at the top.

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Two Distinct Terrains: Continents and Basins In contrast, Venus is completely different

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Crustal Plates: Unique to Earth?

Mountain chains and tectonic activity delineate regions of the Earth's surface.

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Crustal Plates: Unique to Earth?

Mountain chains and tectonic activity delineate regions of the Earth's surface.

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A Thin Crust Enables Activity

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Mantle Convection

Motions in the Earth's interior (think Lava Lamp) fracture and move the crust about.

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Mantle Convection

Motions in the Earth's interior (think Lava Lamp) fracture and move the crust about.

Twenty crustal plates move under this influence (about 1 inch a year)

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Mantle Convection

Motions in the Earth's interior (think Lava Lamp) fracture and move the crust about.

Twenty crustal plates move under this influence (about 1 inch a year)

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Mantle Convection

Motions in the Earth's interior (think Lava Lamp) fracture and move the crust about.

Twenty crustal plates move under this influence (about 1 inch a year)

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Plate Motion Drives Geology

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Making an Ocean

The Atlantic Ocean has swung open in the last 300 million years. Given that amount of time one inch per year is plenty.

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Earthquakes

Earthquakes are the result of “sticky” plate boundaries. Stress builds up followed by a sudden slip.

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Continental Drift Continues

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Continental Drift Continues

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Erosion and Continental Craters

Some of the continental crust is quite old. However, erosion is a powerful force and fresh mountain range (e.g.

the Rockies) can be worn down in just a hundred million years. Craters don't stand much of a chance.

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How Lightly Cratered?