drifting continents & spreading seas pt.2

Question 1

what was invented to gain more info about the sea floor bathymetry

Answer 1

echo sounding (sonar)
- Velocity = distance/time
- Distance = velocity x time

Question 2

what bathymetric features did Sonar mapping delineated

Answer 2

Abyssal plain (~4-5 km below sea level)
Mid-ocean ridges (MORs): submarine mountain ranges (peaks ~2-3 km below sea level)
Fracture zones
Trenches (near land, >5 km)
Volcanic islands
Seamounts, guyots

Question 3

where does the deepest part of the ocean occur

Answer 3

near land

Question 4

some distinct ocean basin / crust features

Answer 4

• A mountain range runs through every ocean basin
• Submarine volcanoes form lines across ocean floors
• mafic (basalt and gabbro) - no granite or metamorphic rocks
• covered by sediment (Thickest & oldest near the continents + Thinnest (or absent) at the mid-ocean ridge)
• High heat flow at the mid-ocean ridge
• Belts of concentrated subsea earthquakes
• Sea-floor spreading

Question 5

explain sea floor spreading

Answer 5

= Upwelling mantle erupts at the mid-ocean ridges
= New crust moves away from ridges, gathering sediment
= At trenches the sea-floor dives back into the mantle
*Provided a potential mechanism for continental drift

Question 6

what measures the strength of Earth’s magnetic field

Answer 6

magnetometer

Question 7

what 2 things does The total magnetic field include

Answer 7

1. Main dipole field generated by Earth’s core
2. Local magnetic field from near-surface rocks

Question 8

whats a Magnetic Anomalie

Answer 8

The difference between expected and actual magnetic field strength
- Can be positive (+) or negative (-)
- they oscillate perpendicular to the mid-ocean ridge (MOR)
- These anomalies form linear belts along the MOR, reflecting magnetic reversals over time

Question 9

what measure the seafloor’s magnetic properties

Answer 9

Towed magnetometers

Question 10

what are magnetic reversals

Answer 10

Earth’s magnetic poles switch places over geological time
- north magnetic pole shifts to the south geographic pole
- Occur geologically rapidly
- Can be dated using radiometric dating
- happen approximately every 500,000 - 700,000 years
- 171 reversals have been recorded since the end of the Cretaceous period

Question 11

what shows evidence of magnetic reversals

Answer 11

Layered lava flows

Question 12

what are positive and negative anomalies

Answer 12

= Positive anomalies – Crust with normal polarity
= Negative anomalies – Crust with reversed polarity
These anomalies create symmetrical patterns on both sides of the mid-ocean ridge (MOR) - Provides strong evidence for seafloor spreading + plate tectonics