How the Earth works Lecture 11: Planetary Geology Flashcards
What is the surface on the Moon and Mars dominated by?
Impact craters
For example the Hellas basin on Mars, which is the 4th or 5th largest impact crater in the solar system.
What are the Polar ice caps on mars affected by?
Seasonal variation
True or False: Atmospheric composition can be roughly determined via using wavelengths of light with a telescope
true
Describe the capabilities of high resolution imaging cameras on Mar’s surface
High resolution imaging cameras are able to see (On Mars):
-800m high dust devils
-500m high cliff avalanche
-New/Young impact craters
Describe the capabilities of the Perseverance rover on mars
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.
Describe the origins of meteorites
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.
What are Analogue sights?
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.
Describe the topography and surface geology of the moon
Highlands
Topographically higher
Heavily cratered
Lighter colour
Plagioclase (anorthite) rich
Maria
Latin for “seas”
Low lying
Smooth, low crater density
Basaltic lavas
What are key findings from the Apollo missions?
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.
Describe the origin of the ‘Maria’
Lava flowed up through cracks in the moons curst and filled its impact basins
What is the main/dominant geological process on the moon?
Hypervelocity impacts are the main driver of geological and topographical features on the moon
Describe Lunar soil
Lunar “soil” is made of pulverized rock created by meteorite impacts.
What is the diamater of Mars
Diameter 6,780 km (~1/2 Earth)
Describe the Topography and surface of Mars
How and why did Olympus mons form
Olympus Mons: product of stagnant lid tectonics and low gravity
How large is Olympus mons?
Rougly double the height and width of Mt Everest and Havaj.
What is the hottest planet in the Solar system
Venus
Describe main characteristics of Venus
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
Describe the atmosphere/atmospheric content of Venus
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
The atmospheres of Earth and Venus are very different, what are some reasons for this?
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?)
What are findings from the Soviet probes Venera 13 & 14
Simple chemical analyses suggest rocks are similar to basalt.
Evidence for weathering processes and some aeolian (wind) activity
Describe the topography/surface of Venus
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)
Describe geological features on Venus
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
Describe Volcanology on Venus
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?
What is the reason/cause for volcanism on Venus
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
Describe evidence for crust compression/deformation (Tesserae)
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
The internal structure of Venus is unknown, however it is known that Venus has no magnetic field, why is this?
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
What is the main tectonic system on Venus (in regards to the release of heat)
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)
Why are there no plate tectonics on venus
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
Describe the history and nature of Venus’s surface
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
How does the size of the planet affects its geological processes?
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
