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Terrestrial World Surfaces

Solid rocky surfaces shaped (to varying degrees) by:
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Impact cratering
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Volcanism
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Tectonics (gross movement of surface by interior forces)
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Erosion (by impacts or by weather)
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The Earth's Surface
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Unlike Mercury and the Moon, impact craters are few and far between on the
Earth.

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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.

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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
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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
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The Earth has two distinct surface levels
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Continents: Thick portions of the crust that occupy high elevations
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Basins: Thiner crust occupying the “lowlands”
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Two Distinct Terrains: Continents and Basins
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Interestingly, there is just enough water on Earth to fill the basins.
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Two Distinct Terrains: Continents and Basins
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Interestingly, there is just enough water on Earth to fill the basins.
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It didn't have to be this way, consider Jupiter's moon Europa
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The world is submerged under a 60 mile deep ocean frozen at the top.
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Two Distinct Terrains: Continents and Basins
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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
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Motions in the Earth's interior (think Lava Lamp) fracture and move the crust
about.
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Mantle Convection
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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
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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
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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?