Week 3: How to build a planet Flashcards
What is the age of the solar system?
4567 Ma
What is used to date the solar system?
Meteorites
How did the solar system form, according to the nebular theory?
sun and planets formed by a gravitational collapse of an interstellar gas and dust at about same time
What is the Principle of Uniformitarianism?
Processes act at similar rates to those observed today
strict uniformitarianism is untenable
James Hutton and Charles Lyell
How does the surface elevation of the Earth vary- where are the highest and lowest points?
Mt Everest 8850m above sea level
Challenger Deep 11,030m below sea level
How do we know the Earth has layers? How can we study the Earth’s interior?
surface rock density is less than 3.5 but whole Earth density is 5.5
Why study meteorites?
iron meteorites have a similar composition to the Earth’s core
What is the internal structure of the Earth?
-Crust
-Mantle
-Liquid iron outer core
-Solid iron inner core
What are the key differences between the internal layers (e.g., chemical and mineral composition, density etc)?
Crust=
-0-40km
-0.4% of mass
Mantle=
-40-2890km
-67.1% of mass
-solid rock
Outer core=
-2890-5150km
-30.8%
-liquid iron
Inner core=
-5150-6370km
-1.7%
-solid iron
What are the differences between continental and oceanic crust?
Continental:
-thicker and less dense (avg 40km)
-more felsic
-derived by a sequence of melting processes
Oceanic:
-thinner and denser (avg 7km)
-composition mafic
-result of mantle melting, deeper levels
What is the Moho and how does it vary?
Mohorivic discontinuity
The crust mantle boundary is marked by a jump in seismic wave velocity
Why is the inner core solid?
does not melt due to the pressure
What defines the start and end of the Hadean?
began with the formation of Earth/the solar system 4567Ma
ended 4030Ma= oldest rocks
What proportion of earth history does the Hadean represent?
earliest history
oldest eon
4567-4030Ma
What is the age of the Earth?
4567Ma
(4030Ma=oldest rocks)
How did the early Earth grow in size (what are the stages)? What processes caused dust and condensing material to accrete into planetesimals? How did planetesimals grow into the inner planets of the solar system?
Growth process has 3 stages:
1.aggregation of micron sized dust to 1-10km planetesimals (via coagulation, accretion + gravitational attraction)
2. runaway growth of largest planetesimals to form planetary embryos
3. aggregation of embryos to form terrestrial planets
What is a planetesimal? What processes caused dust and condensing material to accrete into planetesimals? How did planetesimals grow?
planetesimal=enveloping disk of gas and dust accreted into km sized chunks called planetesimals
planetesimals grow through runaway growth
When and why did the Earth’s interior core and mantle separate?
-core and mantle differentiation will have occurred during the accretion stage of Earth’s evolution
1.early on the Earth was fairly homogenous inside
2.when temperature got hot enough, iron began to melt
3. the iron accumulated at the centre of the planet to form a metallic core
=differentiation
-core formation took place in the first 30Ma of Earth history
What was the source of heat that lead to melting of the Earth?
heat released by impacts
heat created by decay of radioactive elements
What is the age of formation of the Moon?
around 4500 Ma
How did the Moon form?
1.a protoplanet (Theia) collided with the Earth
2.vaporized the mantles of both bodies
3. some of this material retained in Earth orbit= circumsterrestial disc
4from this the Moon accreted shortly afterward
What is the age of oldest zircon and where are they found?
Found in granite rocks
4.40 Ga
4030 Ma are the oldest rocks
What was the composition of the Hadean crust?
-presence of quartz inclusions
-granite formed by melting pre existing basalt crust
-polished surface of a zircon grain
What was the tectonic style of the early Earth in the Hadean and early Archean? What is mean by a ‘stagnant lid’?
-little chemical variation in composition of mafic crust for around 300myrs: crust very long lived
-implies modern plate tectonics not exist in Hadean
-‘stagnant lid’= single fixed plate)
By the end of the Hadean, the Earth had a primitive atmosphere and early oceans. Contrast these with the
oceans and atmosphere today. What were the major gases in the early atmosphere? What gas was not present that is common in the current atmosphere?
-Earth eventually cooled sufficiently for water to condense from atmosphere so crust covered with warm carbonated ocean
-oceans at times cold and icy
-cycles of warming and cooling and ephemeral oceans
-dense CO2 rich atmosphere
-methane from volcanic outgassing
-deep and very toxic (CO2-CO-H2O-H2)
-NO nitrogen
When did liquid water (oceans) form at the Earth’s surface?
After around 10 million years Earth cooled sufficiently for water to condense from atmosphere
What was the fate of the early atmosphere of the Earth?
dense, deep and very toxic
surface too hot for stable, liquid water
What was the character of the Hadean landscape?
sun 70% as luminous as today so if no atmosphere= -47temp if current atmosphere then -25temp
What was the role of impacts in the early Earth?
caused hostile conditions for life
stabilise surface temps and deliver key elements H20 and sulfur
