How the Earth works Lecture 11: Planetary Geology

Question 1

What is the surface on the Moon and Mars dominated by?

Answer 1

Impact craters

For example the Hellas basin on Mars, which is the 4th or 5th largest impact crater in the solar system.

Question 2

What are the Polar ice caps on mars affected by?

Answer 2

Seasonal variation

Question 3

True or False: Atmospheric composition can be roughly determined via using wavelengths of light with a telescope

Answer 3

true

Question 4

Describe the capabilities of high resolution imaging cameras on Mar’s surface

Answer 4

High resolution imaging cameras are able to see (On Mars):
-800m high dust devils
-500m high cliff avalanche
-New/Young impact craters

Question 5

Describe the capabilities of the Perseverance rover on mars

Answer 5

Designed to travel for many KM

Equipped with many tools for chemistry and mineralogy

Has been used to discover and view signs of flowing water in sediment.

Question 6

Describe the origins of meteorites

Answer 6

Carbonaceous chondrites come from Primitive planetesimals

Ordinary chondrites come from metamorphosed

Achondrites come from Differentiated planetesimals.

98% of meteorites are stony
86% of stony meteorites are chondrites
9% of stony meteorites are Achondrites

1% of meteorites are stony iron

Pure iron meteorites are the cores of ancient planets/planetesimals which are knocked loose through mass impact events.

Question 7

What are Analogue sights?

Answer 7

Analogue sites are places on Earth with comparable past or present, geological, environmental or biological conditions of another planetary body.

For example the Copernicus crater on the moon and the Meteor crater in Arizona, USA.

Question 8

Describe the topography and surface geology of the moon

Answer 8

Highlands
Topographically higher
Heavily cratered
Lighter colour
Plagioclase (anorthite) rich

Maria
Latin for “seas”
Low lying
Smooth, low crater density
Basaltic lavas

Question 9

What are key findings from the Apollo missions?

Answer 9

The chemical composition of Moon and Earth rocks are very similar (even oxygen isotopes!)

Anorthositic Highland rocks suggest global lunar magma ocean

Hypervelocity impacts/mass impacts are a dominant geological process on the Moon

Lava flowed up through cracks in the Moon’s crust and filled its impact basins (maria)

Lunar “soil” is made of pulverized rock created by meteorite impacts.

Question 10

Describe the origin of the ‘Maria’

Answer 10

Lava flowed up through cracks in the moons curst and filled its impact basins

Question 11

What is the main/dominant geological process on the moon?

Answer 11

Hypervelocity impacts are the main driver of geological and topographical features on the moon

Question 12

Describe Lunar soil

Answer 12

Lunar “soil” is made of pulverized rock created by meteorite impacts.

Question 13

What is the diamater of Mars

Answer 13

Diameter 6,780 km (~1/2 Earth)

Question 14

Describe the Topography and surface of Mars

Question 15

How and why did Olympus mons form

Answer 15

Olympus Mons: product of stagnant lid tectonics and low gravity

Question 16

How large is Olympus mons?

Answer 16

Rougly double the height and width of Mt Everest and Havaj.

Question 17

What is the hottest planet in the Solar system

Answer 17

Venus

Question 18

Describe main characteristics of Venus

Answer 18

Hottest planet in the Solar System (“Earth’s evil twin”), average surface temperature = 750°K

Similar density and size to Earth

Accreted in similar part of inner Solar system (should be similar in composition)

BUT average surface temperature = 750°K

Atmospheric pressure x90 that on Earth

Question 19

Describe the atmosphere/atmospheric content of Venus

Answer 19

96.5% CO2, rest mostly N2 with trace O2 and water vapour

High surface temperatures due to greenhouse effect

Heat from Sun absorbed by CO2 and sulphuric acid droplets

No cold polar regions

Question 20

The atmospheres of Earth and Venus are very different, what are some reasons for this?

Answer 20

Hadean atmospheres probably very similar.

On Venus, temperatures increased as Sun became hotter – any oceans boiled off?

On Earth, evolution of life consumed CO2 and released O2

CO2 also removed by formation of limestones

If all CO2 removed from terrestrial carbonate rocks, Earth’s atmosphere would be similar to Venus (and half as dense)

CO2 increased in Venus’s atmosphere due to prolonged volcanic activity (as young as <1 Ga?)

Question 21

What are findings from the Soviet probes Venera 13 & 14

Answer 21

Simple chemical analyses suggest rocks are similar to basalt.

Evidence for weathering processes and some aeolian (wind) activity

Question 22

Describe the topography/surface of Venus

Answer 22

Main geological provinces:

Lowlands:
90% flat basins and rolling plains (relief <1km) crossed by narrow deformed zones
Resemble lunar maria
BUT impact craters very rare so surface is relatively YOUNG - < 1 Ga or younger?

Highlands area in the north:
plateau-like , 4-5 km above the low plains, some mountains as high as 11 km (Ishtar Terra in north = size of Australia).

Equatorial upland areas:
broad domes (0-2 km above plains)

Question 23

Describe geological features on Venus

Answer 23

Volcanic rises
1000-2500 km diameter, overlying positive gravity anomalies (mantle plumes)

Impact craters
But not that many – suggests landscape relatively young (<1 Ga!)

Coronae
Circular patterns of ridges and troughs 50-500 km in diameter
Major mechanism of heat loss

Tesserae
Oldest part of lithosphere, with sinuous ridges that are antiformal folds

Question 24

Describe Volcanology on Venus

Answer 24

Volcanic rises
1000-2500 km diameter, overlying positive gravity anomalies (mantle plumes)

showing evidence for multiple lava flows and eruption events (central dome 100 km across and 1 km high)

‘Pancake’ volcanoes: each ~25 km across and ~750 m high = extrusion of viscous magma as lava did not flow very far, resulting in steep sided pancake volcanoes.

Lava fields of Mylitta Fluctus:
Six different lava flows, flowing from south to north
Each 1000s of km long
Similar in scale to the Columbia River basalts in western North America
Venusian lavas presumed to be basaltic

Corona Structures:
50-500 km across
Circular to ovoid ring-like structures, some associated with radiating fractures
Lava flows flow from some ‘arachnoids’
The result of the upwelling of magma under the surface?

Question 25

What is the reason/cause for volcanism on Venus

Answer 25

No evidence for linear belts of volcanoes (analogous to those formed above trenches or as hot –spot tracks),

no evidence for plate tectonics.

Most likely model is volcanism above static MANTLE PLUMES

Meaning that Venusian volcanoes are created due to mantle plumes/hotspots and are static in nature, unlike travelling hotspots on earth - Hawaiian volcano belt.

result of extremely long-lived plume activity

Question 26

Describe evidence for crust compression/deformation (Tesserae)

Answer 26

Narrow ‘ridge belts’ of deformed crust common on the lowlands

Some nearly 5000 km long

The belts on the plains are only about 1 km high so not as high as Earth’s mountains

Question 27

The internal structure of Venus is unknown, however it is known that Venus has no magnetic field, why is this?

Answer 27

Four possibilities/explanations:

First, Venus may be hot enough that the lowermost mantle is still molten.

Next, the core could remain fully molten after the mantle completely solidifies.

However, Venus may have an Earth-like internal structure with a partially frozen core.

Finally, observations do not exclude the (unlikely) possibility that Venus is so cold that the core is entirely solid.

Venus probably formed hot and cooled down over time (albeit the mantle may not cool monotonically due to radiogenic heating) so the internal structure could evolve from left to right over geologic time

Question 28

What is the main tectonic system on Venus (in regards to the release of heat)

Answer 28

On Earth, heat is lost from the core and mantle by plate tectonics and hot-spot activity

On Venus, heat appears to have been lost entirely by hot-spot activity (in the last geological period/1 billion years)

Venus’ surface comprises one planet-encircling plate that is geologically young (<0.5 Ga)

Question 29

Why are there no plate tectonics on venus

Answer 29

Two possible reasons:
1) Lithosphere is too warm to develop rigid plates (remember, surface temperatures hot enough to melt lead)

2) No water to help lubricate subduction zones and lower melting of upper mantle and permit ductile flow

Question 30

Describe the history and nature of Venus’s surface

Answer 30

Venus’ surface comprises one planet-encircling plate that is geologically young (<0.5 Ga)

Did resurfacing(destruction of old surface and creation of new) occur catastrophically or gradually?

Either way, clearly Venus was volcanically active on a large scale until relatively recently

Possible that an early plate tectonic system has been obliterated during resurfacing
BUT
The dominant mechanism for losing heat is hot-spot volcanism

Question 31

How does the size of the planet affects its geological processes?

Answer 31

The size of a planet is critically important – the smaller the planet, the quicker it will cool and the more restricted will be its geological evolution

Venus might be expected to be similar to Earth but the warmth of its lithosphere and lack of water prohibit plate tectonics – at least at the present day

Mars was once very similar to Earth (oceans, volcanoes etc), but cooled & lost magnetic field