Year 9 Science - Earth and Space

layers of the earth

crust, mantle, inner core, outer core

properties of the crust

• 7-50km thick

• rocks, minerals, covered by water

• surface isn't smooth

• thin and brittle

properties of the mantle

• 2800km thick

• 500°C - 3000°C

• molten rock, solid, plastic

• bottom is solid

• rocks move slowly due to convection currents

• source of volcanoes and earthquakes

properties of the core

• consists of outer and inner core

• (unknown thicknesses?)

OUTER:

• 2900-5100km thick

• 4000°C-6000°C

• metals (liquid) - iron, some nickel; not rock

INNER:

• 5100-6370km thick

• 10000°C

• solid iron

major tectonic plates

• pacific plate

• north-american plate

• eurasian plate

• african plate

• antarctic plate

• indo-australian plate

• south-american plate

• nazca plate

movement of tectonic plates

• move through convection currents - core heats up mantle (move matter up) but crust cools it (move matter back down)

• as rock push horizontally against plates, friction between plates and rock cause plates to move

continental drift

• put forth by Alfred Wegener

• all continents once connected together in a supercontinent - Pangaea

• for key observations to support

Gondwana

• southern half of Pangaea supercontinent along with northern half - Laurasia

• final formation occurred ~ 500 mil years ago

• joined now Africa, India, Madagascar, Australia and Antarctica

• multicellular organisms had evolved - primitive

• genetic similarities indicating shared ancestry exist in flora today

continental drift evidence (1)

1. coastlines - seem to fit together like a jigsaw

continental drift evidence (2)

2. fossil evidence - same species of extinct plants and animals found in rocks of same age but on continents that are now widely separated -> organisms lived side by side, lands moved apart after they were dead and fossilised, organisms would not have been able to travel across oceans

• e.g. mesosaurus - swimming reptile but could only swim in freshwater, cynognathus and lystrosaurus - land reptiles that were unable to swim

• coral reefs and coal-forming swamps found in tropical and subtropical environments -> ancient coal seams and coral reefs found in locations where is too cold today -> were alive in warm climate zones, fossils and coal later drifted to new locations of continents

continental drift evidence (3)

3. matching mountains - mountain ranges with same rock types, structure and ages now opposite sides of Atlantic Ocean -> formed as single mountain range that was separated as continent drifted

continental drift evidence (4)

4. glacial striations - grooves and rock deposits left by ancient glaciers found on different continents very close to equator today, indicate that glaciers either formed in middle of ocean and/or covered most of earth, glaciers only form on land and nearer poles -> glaciers were centred over southern land mass close to south pole and continents moved to their present positions