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Transcript
1
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)
2
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.
3
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.
4
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.
5
How Lightly Cratered?
6
How Lightly Cratered?
7
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”
8
Two Distinct Terrains: Continents and Basins

Interestingly, there is just enough water on Earth to fill the basins.
9
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.
10
Two Distinct Terrains: Continents and Basins

In contrast, Venus is completely different
11
Crustal Plates: Unique to Earth?

Mountain chains and tectonic activity delineate regions of the Earth's
surface.
12
Crustal Plates: Unique to Earth?

Mountain chains and tectonic activity delineate regions of the Earth's
surface.
13
A Thin Crust Enables Activity
14
Mantle Convection

Motions in the Earth's interior (think Lava Lamp) fracture and move the crust
about.
15
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)
16
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)
17
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)
18
Plate Motion Drives Geology
19
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.
20
Earthquakes

Earthquakes are the result of “sticky” plate boundaries.

Stress builds up followed by a sudden slip.
21
Continental Drift Continues
22
Continental Drift Continues
23
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.
24
How Lightly Cratered?