Lecture Seven Flashcards
What are the characteristics of basalt?
High in Mg and Fe - rich minerals Dark in colour Makes up oceanic crust on Earth Original crustal material
What are the characteristics of Granite?
High in Ca, Na, K and Si - rich minerals Lighter in colour Makes up continental crust on Earth Needs water to form
How is a crater formed?
Craters form when impacts occur. Usual speed of impact is more than 20km per second. Velocity and some/all mass converted to heat on impact. May cause melting of crater area. Rocks may be ejected large distances - may achieve escape velocity (lowest velocity a body must have to escape the gravitational pull of another body).
Define superposition.
The oldest things is at the bottom of a stack of things. Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.
Define crosscutting.
If something (a) cuts thought something else (b), then (b) must be older than (a).
What are the basic stages in solar system cratering?
Lots of impacts very early on in solar system, as lists of leftovers from planet formation still being attracted by gravity. Decreases with time. The increase again form 4-3.5 billion years - Late Heavy Bombardment - may have been associated with gas giants destabilising the asteroid belt, possibly associated with the reason Uranus rotates strangely. LHB responsible for larger craters ‘mare’ on moon.
Describe the features of Mercury.
Inner most planet. Pocky basaltic crust. High in Fe and Ni. Trace atmosphere of H and He. Surface temperature varies form 100-700K, with average of 452K. Gravitationally locked to the Sun, so that one day on Mercury lasts for two Earth years. One face of Mercury always faces the Sun.
Describe the structure of Mercury.
1/3 the size of Earth, but the same density. This suggests that the core makes up 60% of planetary radius. Core probably composed of 60-70% Fe by mass. Dipolar magnetic field found, so core may be partially molten. Rocky mantle surrounds core, with crust ~100km thick. Heavily cratered surface retaining evidence of 4 billion year old bombardment (no weathering or erosion because there is no atmosphere).
Describe the characteristics of Venus.
Second planet form the Sun. Rocky basaltic crust. Thick atmosphere of CO2, N2, H2O, H2SO4 vapour. Surface temperature always 726K - massive greenhouse gas effect. Rotates very slowly on axis in opposite direction to other planets. 1 Venus day = 243 Earth days. Has not internally generated magnetic field - core probably entirely molten. Pictures and soil samples taken from Soviet landers show basaltic soil and crust.
Why does Venus spin the wrong way?
Not sure - but it is likely that something very big hit it about 500-800 million years ago. So surface feats older than that, all craters are younger. Momentum from impact could have slowed and then reversed the spin direction. Before the impact, Venus could have has water like the Earth does (oceans, lakes etc).
Describe the characteristics of the Earth.
Third planet from the sun. Rocky basalt and granit crust, over Mg and Fe rich mantle, over Ni and Fe core. N2 and O2 atmosphere. Water at surface in frozen, liquid and gaseous form. Surface temperatures between 260-310K, with average of 281K. Crust is thinner than on similar planets due to moon forming impact. Thin crust allows for subduction an rifting to occur, and allows constant recycling of old basaltic oceanic crust. Subduction forms granitic crust = continents are unique to Earth. The Earth and Moon are actually a binary planet system, orbiting around one another.
Describe the characteristics of the Moon.
Rocky basaltic crust. No atmosphere. Tidally locked so one face always faces the earth. Think basaltic crust, over thick basaltic mantle, over solid core. The core is <4% of the Moon mass, core is mostly basaltic as well. Water may be found in the polar areas of the moon, possibly ice from comet impacts.
Describe the characteristics of Mars.
Fourth planet from the Sun. Rocky basaltic crust, with areas of granitic sand at old hot springs. Thin atmosphere of CO2, N2 and Ar. Surface temperature varies from 150-310K. Has liquid water in rock layers just below surface. Has water ice clouds in sky. ~1/3 of Earth size, lower in density. Core thought to be partially or fully molten. Surface of Mars tidally bulges 1cm in response to the position of the Sun - this requires a totally or partially molten core to occur. No significant magnetic field, so no rotational difference between inner and outer core. Evidence of magnetic field in the early history of Mars. Northern plains of Mars are lower and thinner curst then Souther highlands, due to the original Northern curst being torn off by an early impact - now one of Mars’ moons.
Describe meteorites.
Three groups: Stoney: - Chondrites (contain round particles) “chondrules” that show they formed in zero-gravity. - Achondrites (rounded particles have melted together under the influence of gravity) once part of planetismals or planets. Stony Iron: - Pallasites (combination of Achondrite and Iron) part of core-mantle boundary of planetismal. Iron meteorites: - Nickel-iron allow, cooled slowly (part of cores of planetismals).
Draw the tbale of comparision of terestrial planets.
