Black Earth, Blue Earth, Grey Earth

Question 1

What pieces of evidence indicate a ‘big-bang’ origin of the universe 12 Gyr ago? (4)

Answer 1

• Most galaxies are red-shifted (expansion)
• Mass fraction of He is 25% (fits predictions)
• Age of the oldest clusters of stars is ~12Gyr
• Cosmic background radiation is a perfect black body with small fluctuations (fits big bang model)

Question 2

What are the steps in the formation of a spiral galaxy?

Answer 2

1. Bodies of gas, dust and young stars collide
2. Rotation around a central mass
3. Rotation contracts cloud into a galactic disk
4. Motion creates spiral arms

Question 3

How are atoms heavier than Fe formed? Why?

Answer 3

Via a supernovae explosion, as above iron excess energy is needed (elements beforehand release energy on formation)

Question 4

How are planets formed?

Answer 4

1. Dust grains collect into chondrites
2. Accretion I: forms asteroids (planetesimals)
3. Accretion II: forms planets

Question 5

Why is the universe less habitable if the C/O ratio > 1

Answer 5

As carbon will preferentially bind to silicates which are harder to weather and produce plate tectonics and water cycles

Question 6

What pieces of evidence give the age of the Earth?

Answer 6

• Oldest rocks (iceland) dated to 3.7-3.8 Ga
• Oldest minerals dated 4.4 Ga
• Oldest moon rocks dates 4.4-4.5 Ga
• Canyon el Diablo Meteorite lead 4.55 Ga

Question 7

What are two hypotheses for the delivery of water to the Earth?

Answer 7

1. Delivered via asteroids which have a low water content but many collisions
2. Delivered via comets which have a high water content but fewer collisions occur

Question 8

Why is water important for life?

Answer 8

• good polar solvent
• high surface tension allows transport in vascular plants
• ice is less dense!

Question 9

Describe the rock cycle

Answer 9

Igneous rock forms from melting and cooling which then forms metamorphic rock by heat and pressure (e.g granite) which can then forms sedimentary rock by erosion and compaction

Question 10

Name 4 pieces of evidence for plate tectonics

Answer 10

1. Fossil distributions across oceans
2. Land matching
3. Seismic activity at plate boundaries
4. Mountain ranges and mid-Atlantic ridge