Week 1- DYNAMIC PLANET: The Earth System and Unit Content

Question 1

What are the 5 main spheres of the Earth?

Answer 1

1. Atmosphere (gases)
2. Cryosphere (ice)
3. Hydrosphere (water (liquid))
4. Biosphere (sum of all life)
   5.Geosphere:
   -lithosphere (hard rock) (this can be seen as a sphere in its entirety instead of geosphere in general)
   -asthenosphere
   -remaining mantle
   -outer and inner core

Question 2

What does the atmosphere consist of?

Answer 2

-this is the gaseous envelope that surrounds the Earth
-includes gases themselves and their chemical composition
-also liquid water droplets/ ice particles that comprise clouds and precipitation
-dust particles
-other aerosol particles suspended in air

Question 3

What does the cryosphere consist of?

Answer 3

Everything frozen on the Earth’s surface
-polar caps
-glaciers in mountains
-sea ice
- permafrost on soils

Question 4

What does the hydrosphere consist of?

Answer 4

Includes all the water substance on the Earth in its liquid form
-oceans
-any fresh water: lakes, rivers, groundwater…

Question 5

What does the lithosphere consist of?

Answer 5

comprises the upper part of the Earth’s surface
maybe down to a few tens of km deep from the Earth’s surface.
It doesn’t include
the deepest parts of the Earth’s mantle

Question 6

What are climate forcing’s and responses?

Answer 6

cause and effect
external forcings= causes
internal responses= the change that results in the Earth’s climate

Question 7

What are some examples of external forcings?

Answer 7

plate tectonics
orbital changes
solar input

Question 9

What is positive feedback?

Answer 9

Positive feedback:
process internal to the Earth’s that acts to enhance the original action

Example: water vapor feedback=
-if Earth’s air temp increases then atmosphere has greater capacity to incorporate water vapour into it, this leads to an increase in evaporation putting more water vapour in air, since this is a greenhouse gas it increases the air temperature.
-So the idea is that the initial increase led to a further increase in air temp hence positive feedback

sometimes positive and negative offset each other

Question 10

What is negative feedback?

Answer 10

process that counteracts the initial action

Example: cloud feedback
-if we increase the air temperature of the atmosphere it will lead to an increase in evaporation which will put more water vapour in the air so clouds more likely to form leading to more reflection of incoming so less radiation reaches the Earth surface so decrease in atmospheric air temperature
-So the idea is that the initial increase led to a decrease.

sometimes positive and negative offset each other

Question 11

Where did the ocean and the atmosphere come from?

Answer 11

repeated melting of the Earth led to differentiation of internal structure (crust, mantle, core)

volatiles expelled as volcanic gases

Question 12

How was the second atmosphere formed? What was its composition?

Answer 12

How= Outgassing produced the second atmosphere

Composition: nitrogen, carbon dioxide, water vapour, ammonia, hydrogen sulphide, sulphur dioxide (that was being emitted from the Earth and volcanoes)

Water vapour cooled by the planet so condenses along with soluble gases (such as sulphur dioxide) to form our first oceans
leaves nitrogen and CO2 dominant
some have argued that nitrogen also arrived by comets, was released by denitrifying bacteria or from the oxidation of ammonia
that nitrogen used more or less its current concentration early in the Life Time

Question 13

Compare current nitrogen concentration to that of the second atmosphere?

Answer 13

current= 0.79bar (78%)
past= study by Marty et al in 2013 looked at fluid inclusions in hydrothermal courts that had an age of between 3 and a 3.5 billion years ago showed that the isotopic ratios of nitrogen where about the same as we have at present.
-partial pressure was 0.5-1.1 bar

Question 14

Where did carbon dioxide come from?

Answer 14

today= much carbon stored as organic matter and in limestone (calcium carbonate)

These didn’t exist in early PreCambrian before there was any life

if all carbon in these storehouses was converted to co2 then concentrations would be 100-1000 times present levels in atmosphere (0.04%)

Question 15

When did O2 appear in atmosphere?

Answer 15

earliest atmosphere would have had no oxygen (21% today)

Oxygen was not outgassed from Earth’s interior unlike other elements

the only abundant source is from photosynthesis

since other planets lack oxygen in their atmosphere it provides evidence that without life we wouldn’t have a lot of oxygen

Question 16

What is an abiotic source of oxygen on Earth?

Answer 16

UV radiation can photodissociate water vapor

2H2O + UV radiation = 2H2 + O2

Would produce only small amounts (perhaps 10–7 times the present amount).

Question 17

When did a rapid increase in oxygen concentration occur?

Answer 17

started around 2.5Ga
The Great Oxygenation Event

as more and more oxygen was added to the atmosphere we eventually reached the current value of 21% oxygen that we see today

Question 18

Why has Earth’s climate been stable?

Answer 18

-A condition for sustained life is that the Earth’s temperature hasn’t fluctuated too wildly.

-Higher CO2 levels during the Proterozoic would mean quite a strong greenhouse effect.

-Then, gradual cooling as CO2 decreased.

-In fact, the Earth seems to have maintained an average temperature of about 15–25°C

-Sun’s brightness has increased by 25–30% during the lifetime of the Earth

-Faint Young Sun Paradox.

To keep temperature within a narrow range, something would have to balance increase in solar radiation.

Question 19

What is the feedback between Solar Radiation and Removal of Carbon Dioxide?

Answer 19

One estimate: CO2 pressure was as large as 10 atmospheres! (refuted by Marty et al. 2013)

If Sun is stronger, oceans warm.
-Evaporation increases.
-Rainfall increases.
-Continents are weathered more.
-Weathering removes CO2 from the atmosphere.

Question 20

What are solutions to the Faint Young Sun paradox?

Answer 20

1. Feedback between Solar Radiation and Removal of Carbon Dioxide
2. Methane as much as 100 parts per million (currently about 1.7 ppm) could have offset the faint sun.
3. Lower albedo (less continental area).
4. Different models for the evolution of the Sun.

Question 21

What was the early Archean atmosphere like in summary?

Answer 21

-very little oxygen
-nitrogen concentrations around the same as present
-CO2 and methane could have been higher to offset the Faint Young Sun Paradox

Question 22

What 2 main gases make up the universe?

Answer 22

helium 36.6%
hydrogen 60.4%

Question 23

What 2 main gases make up the atmosphere?

Answer 23

Oxygen 21%
nitrogen 78%

Question 24

What 2 main gases make up the cryosphere and the hydrosphere?

Answer 24

oxygen 86%
hydrogen 11%

Question 25

what gases make up the geosphere?

Answer 25

Iron
oxygen
silicon
magnesium
nickel
calcium
aluminium
and others

Question 26

What is the hydrological cycle driven by?

Answer 26

the climate system
driven by the sun’s energy

Question 27

What is the rock cycle driven by?

Answer 27

tectonics
driven by the Earth’s internal heat

Question 28

What are geochemical cycles of mass?

Answer 28

the cycle of mass (elements) between the different Earth spheres (or reservoirs)?
-they are complex
happen because:
-heat (energy) is unevenly distributed

Question 29

What affects geochemical cycles?

Answer 29

-Earth spins= night and day
-Earth revolves around the sun on a plane= climate belts
-Earth is tilted= seasons
-Earth is not spherical and not materially heterogeneous= some bits just warm up faster than others
-these are SOME reasons

Question 30

How do these create geochemical cycles?

Answer 30

generate temperature and pressure gradients in the Earth system
mass and energy move through gradients
mass can be moved to a new position where new temperature/pressure profile cause it to become unstable
phase or chemical reactions from materials with different physical properties- Gravity is important

Question 31

What does the hydrological cycle describe?

Answer 31

how water flows through the Earth system

Question 32

What is the rock cycle?

Answer 32

-the concept that rocks change their physical and chemical properties when they are forced out of their equilibrium conditions
-not a simple “circular” cycle

Question 33

What are the principal controls that drive the rock cycle?

Answer 33

-changes in T and P mainly driven by tectonics
-aided by the hydrological cycle, gravity and sometimes life

Question 34

Compare the “chemical” model vs the “mechanical” model of the structure of the Solid Earth? Which is most useful in understanding tectonics/rock cycle?

Answer 34

Chemical:
-based= major changes in composition
-crust, mantle and core (inner and outer)

Mechanical:
-based= changes in the rheological (flow) behaviour
-lithosphere, asthenosphere, outer core and inner core
-more useful

Question 35

How do the following plate boundaries affect the lithosphere thickness? (divergent, convergent and conservative)

Answer 35

Divergent= thinning
Convergent= thickening
Conservative= little change

Question 36

What is the structure of the solid Earth? (lithosphere and asthenosphere?

Answer 36

lithosphere=
-30-70km thick
-rigid enough to comprise a number of relatively coherent plates
-plates move relative to each other- due asthenospheric deformation
-brittle
Composition:
-continental (granitic)= 2.8g/cm3
-oceanic (basaltic)= 3.0g/cm3

asthenosphere=
-to 2900km depth
-weak
-low rates of ductile deformation- due to thermal gradients (convection)
-plastic
Composition:
-periodotite= >3.3g/cm3

Question 37

Describe the Wilson Cycle?

Answer 37

1. mature (eroded) continental crust
   2 continental rifting
2. formation of first oceanic crust
3. mature ocean formed
4. incipience of ocean-continent subduction
5. closing ocean (subduction of spreading centre)
6. docking of continents= orogenesis