Ch. 9.2} Shaping Planetary Surfaces

How can we estimate the age of a surface region on rocky planets such as Mercury?

***********Measuring the depth of the craters

Examples of places in the US that was built by erosion

- Grand Canyon} Erosion by water - Yosemite} Erosion by glaciers - Deserts} Erosion by wind - River Deltas} Erosion by water

Central peak

- In larger crater (typically craters 20k or larger), the center will compress and rebound forming a peak in the center of the crater

Tectonics

- The "building" of surface features by stretching, compression, or by other forces acting on the lithosphere via stretching, and compression *Involves convection cells underneath the surface *Tectonic is the Greek work for "builder"

Impact cratering

- The creation of bowl-shaped impact craters by asteroids or comets striking a planet's surface

What happens during tectonic activity?

- The crust can be compressed in places where adjacent convection cells push rock together (This type of compression helped create the Appalachian Mountains) - Cracks and valleys form in places where adjacent convection cells pull the crust apart

Volcanism

- The eruption of molten rock, or lava, from a planet's interior onto its surface - Any eruption of molten lava ex. volcanoes - Usually along a crack in a planet's surface

The stronger an impact from an impact crater is the...?

- The larger the crater walls are - The more impressive the central peak is - The deeper the hole is

Tectonic activity

- The movement of plates within the earth's crust against each other, contributing to volcanic eruptions and massive earthquakes - Requires internal heat - Direct result of mantle convection

How were plates formed?

- The ongoing stress of mantle convection fractured the lithosphere into more than a dozen different pieces or plates

Plate tectonics

- The theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle

Erosion

- The wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather - The breakdown or transport of surface rock through the action of ice, liquid, or gas *Note: Erosion can break down and build up

What are some features of erosion?

- Valleys carved by glacial ice - Canyons carved by rivers - Sand dunes & rivers} Examples of features built up by erosion - River deltas made of sediments carried down stream

What are the features of a crater?

1) Crater wall 2) Central peak 3) Ejecta 4) Ejecta blanket 5) Secondary craters

What processes shape planetary surfaces?

1) Impact cratering 2) Volcanism 3) Tectonics 4) Erosion

What are the 3 main reasons molten rock rises?

1) It is less dense than solid rock 2) The solid rock surrounding the chamber of molten rock can squeeze the molten rock driving it upward under pressure 3) Molten rock often contains trapped gases that expand as it rises which can make it rise much faster and lead to dramatic eruptions

What does an impact crater form?

1) The leftover planetesimal (typically asteroid or comet) slams into a solid surface b/w 40,000 and 250,000 km/hr 2) This causes the impact to release enough energy to vaporize solid rock and blast out a crater 3)Debris from this blast will shoot high above and then rain over the area *If this impact is large enough, some of the ejected material can escape into space *However, small craters usually outnumber large ones

Secondary craters

A crater formed by the impact of debris ejected from a larger crater

What was the result of outgassing?

All the gas that made the atmosphere of Venus, Earth, and Mars, and the water vapor that rained down to form Earth's oceans, originally was released from the planetary interiors by outgassing

Lunar maria

Dark regions of the moon

What does the result of an eruption depend on?

How easily the molten rock flows across the surface *Lava that is runny can flow far before cooling and solidifying *Lava that is thicker tends to collect in one place and build upward

The fact that the amount of small craters that impact celestial bodies outnumbers the amount of large craters demonstrates what?

It demonstrates that more small planetesimals formed during the birth of our solar system and that more small leftovers still orbit the sun today!

What does dating craters allow for?

It provides us with an estimation of the geological age of a surface region - Young} Have formed relatively recently - Old} Have formed billions of years ago *Larger number of surface craters typically mean an older surface

Plates

Large pieces of earths crust that move due to convection currents

Lunar highlands

Light regions of the moon

Ejecta

Material that falls back to the surface after being blasted out by the impact of a space object

Ejecta blanket

Material thrown from the inside of a crater during impact, surrounds the formed crater creating this "blanket"

What is the name of the oldest crater and where is it located?

Name} Manicouagan crater Location} Canada

What is the main reason we don't see many craters on Earth's surface?

Tectonic plates! *Over time, craters can be drawn underground by tectonic activity and therefore erased

Geological age

The age of the surface as it now appears *A geologically young surface is dominated by features that have formed relatively recently in the history of the solar system *A geologically old surface still looks the same as it did billions of years ago

Crater wall

The inclosing rock wall of a crater; as sometimes used, the steep in-face of this bounding wall.

Outgassing

The process of releasing gases from a planetary interior, usually through volcanic eruptions or volcanic vents

How do impact craters reveal a surface's geological age?

We can estimate the geological age of any surface region from its number of impact of craters, with more craters indicating an older surface

When does Volcanism occur?

When molten rock finds a path to the surface