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Lesson4d. Working out the global history of Mars. There is much less water at a deep of one meter, near the equator of Mars, compared to the polar regions. At lower latitudes (near equator) the temperature is higher than at the poles.
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Lesson4d Working out the global history of Mars
There is much less water at a deep of one meter, near the equator of Mars, compared to the polar regions. • At lower latitudes (near equator) the temperature is higher than at the poles. • This can cause ice near the surface, at low latitudes, to melt and then evaporate away. • The measurement doesn’t show that there is no underground water at low latitudes on Mars. • It only shows that there is little water at a depth of one meter, at low latitudes.
Geologic history of Mars • If you consider that a surface that has not been destroyed for billions of years will have a large impact crater density it is possible to tell where most of the geologic history of Mars has taken place.
Which hemisphere is younger • Northern • Southern
Evidence of Plate tectonics on Mars? • Yes • No
Evidence of Plate tectonics • Mountain ranges along plate boundaries • Strato-volcanoes over subduction zones. • Although there are ridges that might be construed as some type of mountain range, there are no strato-volcanoes on Mars. • All volcanoes are shield volcanoes with gently sloping sides due to the low viscosity of the lava.
Tectonics vs. Plate Tectonics • Remember tectonics is changes due to motions in the crust. This includes graben, fissures, stress fractures, volcanism. • Plate tectonics is the whole sale motion of large portions of crustal materials. Like the motion of North and South America. • Although it is very clear that the Tharsis bulge area has had lots of tectonism, there is little evidence of plate tectonics on Mars.
. • Lack of thick atmosphere allows volcanoes to grow large on Mars • No strato-volcanoes means lava has to come out of shield volcanoes making them large • No plate tectonics so same lithosphere stays over the magma plume
Plate tectonics makes new volcanoes as crust moves over magma plume
Let’s use what we have learned • Mars is much smaller than the Earth. This means that is also cooled much more rapidly, causing a thick crust to form rapidly.
When Earth’s crust was still molten, Mars already had a well established surface.
Let’s use what we have learned • Mars is much smaller than the Earth. This means that is also cooled much more rapidly, causing a thick crust to form rapidly. • (Surface Area/Volume)earth = 3/6371 = 0.00047 • (Surface Area/Volume)mars = 3/3397 = 0.00088 • Mars cooled faster than Earth by a factor of 2. • This set up a thick crust with little time for plate tectonics.
Mars was still hot on the inside but was not able to release this heat through plate tectonics. • Instead a single, enormous magma plume developed in one region of Mars. The Tharsis Bulge.
Mars was still hot on the inside but was not able to release this heat through plate tectonics. • Instead a single, enormous magma plume developed in one region of Mars. The Tharsis Bulge. • Mantle plume caused uplift of crust in the Tharsis region. Pressure from uplift allowed shield volcanoes to form, which contributed to layers of lava on top of the Tharsis region. • This created great overlying weight in region.
Eventually the magma plume subsided and the weight of the Tharsis region caused portions of the bulge to sink down. • http://www.google.com/mars/
Eventually the magma plume subsided and the weight of the Tharsis region caused portions of the bulge to sink down. • http://www.google.com/mars/ • The result of portions sinking is an enormous graben feature that formed VallesMarineris. • Uplift and retreat of Tharsis region likely happens multiple times.
This activity pumped energy into the Tharsis region in the form of stress heat and underground magma chambers. • There are signs of lava flow away from the Tharsis region. There is also evidence of water flow that originated from heated underground ice deposits. • http://www.google.com/mars/
What about the North? • There is a strange dichotomy between the northern and southern hemispheres on Mars. • The crust in the Southern hemisphere is very thick and old. The Northern hemisphere is very low. • What about relative age of the regions?
Possibilities • Giant collision with asteroid that removed the crust in the Northern Hemisphere. This is similar to the theory that Earth had two moons which gently collided and spread a thicker crust onto the farside of the Moon.
Possibilities • Giant collision with asteroid that removed the crust in the Northern Hemisphere. • Entire global lithosphere of Mars rotated. This could happen if magma plume builds up crust from underneath very early on in Mars history.
Possibilities • Giant collision with asteroid that removed the crust in the Northern Hemisphere. • Entire global lithosphere of Mars rotated. This could happen if magma plume builds up crust from underneath very early on in Mars history. • Could the Northern hemisphere be an ancient ocean bed?
What would be required for the Northern Hemisphere to be the floor of an ancient ocean?
What would be required for Mars to have an ocean? • Lots of water • Thick atmosphere • No polar ice caps • Living creatures
Did Mars ever have a thicker atmosphere? Evidence would be if there was ever standing water on Mars. Spirit and Opportunity think so. Both landed on Mars in January 2004. Opportunity is still actively researching Mars.
Hematite signal from orbitHematite is an iron compound which typically forms in the presence of water
