Week 3: How to build a planet

Question 1

What is the age of the solar system?

Answer 1

4567 Ma

Question 2

What is used to date the solar system?

Answer 2

Meteorites

Question 3

How did the solar system form, according to the nebular theory?

Answer 3

sun and planets formed by a gravitational collapse of an interstellar gas and dust at about same time

Question 4

What is the Principle of Uniformitarianism?

Answer 4

Processes act at similar rates to those observed today
strict uniformitarianism is untenable
James Hutton and Charles Lyell

Question 5

How does the surface elevation of the Earth vary- where are the highest and lowest points?

Answer 5

Mt Everest 8850m above sea level
Challenger Deep 11,030m below sea level

Question 6

How do we know the Earth has layers? How can we study the Earth’s interior?

Answer 6

surface rock density is less than 3.5 but whole Earth density is 5.5

Question 7

Why study meteorites?

Answer 7

iron meteorites have a similar composition to the Earth’s core

Question 8

What is the internal structure of the Earth?

Answer 8

-Crust
-Mantle
-Liquid iron outer core
-Solid iron inner core

Question 9

What are the key differences between the internal layers (e.g., chemical and mineral composition, density etc)?

Answer 9

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

Question 10

What are the differences between continental and oceanic crust?

Answer 10

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

Question 11

What is the Moho and how does it vary?

Answer 11

Mohorivic discontinuity
The crust mantle boundary is marked by a jump in seismic wave velocity

Question 12

Why is the inner core solid?

Answer 12

does not melt due to the pressure

Question 13

What defines the start and end of the Hadean?

Answer 13

began with the formation of Earth/the solar system 4567Ma
ended 4030Ma= oldest rocks

Question 14

What proportion of earth history does the Hadean represent?

Answer 14

earliest history
oldest eon
4567-4030Ma

Question 15

What is the age of the Earth?

Answer 15

4567Ma
(4030Ma=oldest rocks)

Question 16

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?

Answer 16

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

Question 17

What is a planetesimal? What processes caused dust and condensing material to accrete into planetesimals? How did planetesimals grow?

Answer 17

planetesimal=enveloping disk of gas and dust accreted into km sized chunks called planetesimals

planetesimals grow through runaway growth

Question 18

When and why did the Earth’s interior core and mantle separate?

Answer 18

-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

Question 19

What was the source of heat that lead to melting of the Earth?

Answer 19

heat released by impacts
heat created by decay of radioactive elements

Question 20

What is the age of formation of the Moon?

Answer 20

around 4500 Ma

Question 21

How did the Moon form?

Answer 21

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

Question 22

What is the age of oldest zircon and where are they found?

Answer 22

Found in granite rocks
4.40 Ga
4030 Ma are the oldest rocks

Question 23

What was the composition of the Hadean crust?

Answer 23

-presence of quartz inclusions
-granite formed by melting pre existing basalt crust
-polished surface of a zircon grain

Question 24

What was the tectonic style of the early Earth in the Hadean and early Archean? What is mean by a ‘stagnant lid’?

Answer 24

-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)

Question 25

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?

Answer 25

-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

Question 26

When did liquid water (oceans) form at the Earth’s surface?

Answer 26

After around 10 million years Earth cooled sufficiently for water to condense from atmosphere

Question 27

What was the fate of the early atmosphere of the Earth?

Answer 27

dense, deep and very toxic
surface too hot for stable, liquid water

Question 28

What was the character of the Hadean landscape?

Answer 28

sun 70% as luminous as today so if no atmosphere= -47temp if current atmosphere then -25temp

Question 29

What was the role of impacts in the early Earth?

Answer 29

caused hostile conditions for life
stabilise surface temps and deliver key elements H20 and sulfur