Earth’s layers have different properties. 6-70 km thick 0-700 °C Cooler rock Crust 2900 km thick 870-4400 °C heated rock Mantle 2300 km thick 4400-6100 °C liquid metals Outer Core 2400 km diameter 7000-8000°C solid metals Inner Core Thickness Temperature Composition Layer Earth’s Layers
Earth’s magnetic poles have switched places several times.
See Page 24
These magnetic reversals are caused by changes in Earth’s magnetic fields. Bands of rock record periods of magnetic reversals. As molten material cools, magnetic minerals line up with the magnetic field. When it hardens, the minerals act like tiny compass needles. See Page 24
Continents split apart at divergent boundaries.
Divergent boundaries on continents produce rift valleys.
Magma rises through cracks and forms volcanoes.
As rift valleys grow wider, continents split apart.
If the valley continues to widen, the thinned floor sinks below sea level.
Hot spots can be used to track plate movements.
Hot Spot: an area of volcanic activity that develops above where magma rises in a plume from the mantle.
Can be used to measure plate movement because it generally stays in one place as the tectonic plate above it moves.
Can provide a fixed point for measuring the speed and direction of plate movements.
The Hawaiian islands are located in the middle of the Pacific Plate. The largest island, Hawaii, is still over the hot spot.
When the plate moves on, it carries the first volcano away from the hot spot. Heat from the mantle plume will then melt the rock at a new site, forming a new volcano. See Page 28
Section 1.4 Plates Converge or Scrape Past Each Other.
Tectonic plates push together and form three types of convergent boundaries. Continental-continental collision: Two continental plates collide, crumpling and folding the rock between them. Mountains could form.
Continued Oceanic-oceanic subductions: two oceanic plates collide and the older, denser plate sinks beneath the top plate, forming deep-ocean trenches and island arcs.
Continued Oceanic-continental subductions: an oceanic plate sinks beneath a continental plate, forming a deep-ocean trench and volcanic coastal mountains.