1.2 Seafloor spreading

Question 1

Seafloor spreading

Answer 1

1. 2 plates move away from each other at divergent plate boundaries, seafloor spreading occurs
2. Magma from deep within the earth rises through the mid-ocean ridge
3. New oceanic crust is formed

Question 2

Finding age of rocks

Answer 2

• using radioactive dating
• as magma rises and cools along crests of mid-oceanic ridges, elements within it crystallise into minerals, forming ingenious rocks
• age of rocks can be determines by measuring remanding concentration of radioactive elements, which reveals how long ago the magma had crystallised

Question 3

Evidence of seafloor spreading supporting plate tectonic theory

Answer 3

• age of rocks ar seabed shows a pattern:
  1. Rocks nearer to the crest (centre) of the mid-ocean ridge are the youngests
  2. Rocks further away from the ridge are progressively older
• shows how new oceanic crust is created at divergent boundaries and then moves laterally on both sides of the mid-oceanic ridge as seafloor spreading continues
• little sediment accumulation is found at oceanic trenches, as older oceanic crust is being destroyed at oceanic trenches
• as a result, oceanic crusts are younger than continental crusts
• proves that new crusts is continually formed at divergent boundaries at the mid-oceanic ridges, and as plates moves, older crust is destroyed further away at oceanic trenches.

Question 4

Sediment accumulation on youthful oceanic crusts

Answer 4

• seafloor is covered by a variety of sediments except along the crests of mid-ocean ridges where newly formed oceanic crusts had not accumulated many sediments
• sediment thickness ranges from about 1000 metres in atlantic ocean to as thin as 300 metres in pacific ocean

Question 5

Mid-oceanic Ridges

Answer 5

• is a part of a system of interconnected underwater mountain chains that run through the world’s oceans
• along crests of mid-ocean ridges, magma wells up between 2 parting tectonic plates, cools then solidifies
• magma cools as temp on Earth’s surface is lower than its interior

Question 6

New Oceanic crusts

Answer 6

• continuous formation of new seafloor supports plate movement theory
• along Mid-Atlantic Ridge is considered a slowly spreading ridge characterised by tall-cliffs and mountains
• more rapidly spreading ridges like East Pacific Rise have gentler slopes
• like Mid-Atlantic Ridge, magma wells up along crests of East Pacific rise, cools before moving away towards either side of the crest, forming new oceanic crusts
• unlike mid-atlantic ridge, surface of East pacific rise is smooth and flat