3.5; 1a. Structure of the Earth + Evidence of Continental Drift/ Continents Flashcards
What are the 3 compositional/ concentric layers of the Earth?
The crust, mantle and the core.
What is the crust and how thick is it?
- The crust is the outer layer of the Earth, made up of continental and oceanic crust.
- It is 5-70km thick.
What is the mantle and how thick is it?
- The mantle is a dense layer of hot semi-solid rock.
- It is 2,900 km thick.
What is the Moho?
The boundary between the crust and the mantle. It lies at 35 km below continents and 10-15 km below the ocean floor.
What is the outer core and how thick is it?
- The outer crust is the layer surrounding the inner core. It is a liquid layer made up of iron and nickel.
- It is 2,200km thick.
What is the inner core and how thick is it?
- The solid and hottest (up to 5,500 °C)part of the Earth, it is found in the centre. Also made up of iron and nickel.
- It is 1,250 km thick.
Outline the key features of oceanic crust?
It is mainly basaltic, silicon and magnesium.
It has a density of 3 kg/m3.
It is about 5-10km thick.
Age: 0-4000 MA.
It is subductable (heavier). -> Constantly being subducted and remade.
Originates from sea-floor spreading.
Outlines the key features of continental crust?
It is mainly made up of granite, silicon and aluminium.
It has a density of 2.7g/cm3.
It is 30-70km thick.
Age: 0-200 MA.
It is not subductable.
Is thickest at the mountain range.
Originates from volcanoes and accretions. (Subducts, volcanic activity builds up continental crust //// Accretion adds material to the crust as fragments of oceanic crust are ‘stuck’ on continental margins during subduction).
What are the mechanical layers of the Earth?
The lithosphere, the asthenosphere, the mesopshere, the outer and inner crust.
What is the lithosphere?
- Is a hard and rigid outer layer made up of the crust and uppermost mantle.
What is the asthenosphere?
The layer below the lithosphere, and extends 100-300km down in the upper mantle.
It is semi-molten and is capable of flowing slowly under pressure.
Convection currents exist in the asthenosphere formed from the intense heat in the low mantle, allowing it to carry the lithosphere.
What is the mesosphere?
The lower part of the mantle situated above the outer core. It is made up of primarily solid rock that are under high pressure and temperature.
What was Wegener’s theory of continental drift?
- In 1912, Wegener proposed that in the Carboniferous period, 250 million years ago, a single large continent called Pangaea existed.
- This slowly drifted or broke apart into 2 large land masses: Gondwanaland and Laurasia.
- However as he could not find a mechanism for the movement his theory was largely ignored.
What geological evidence did Wegener provide for his theory of continental drift?
- Idea of ‘jigsaw’ fit between the east coast of South America and West Coast of Africa.
- Mountain chains and some rock sequences on either side of oceans show great similarity such as NE Canada and N Scotland.
- Evidence from 290 million years ago of the effects of contemporaneous glaciation in places such as Africa and Australia suggest these land masses were joined at this time, close to the South Pole.
What biological evidence did Wegener provide for his theory of continental drift?
- Similar fossil animals found in South America and Australia, especially marsupials.
- Similar fossil marine shellfish found in Australian and Indian limestone.
- Fossils from rocks younger than the carboniferous period in places such as Australia and India showing fewer similarities, suggesting they followed different evolutionary paths.
GEOLOGICAL: Explain in greater detail paleoclimatic evidence.
- Glaciers spread from a central point outwards.
- Glacial deposits formed during the Permo-Carboniferous glaciation are found in Antarctica, Africa, South America, India and Australia.
- Glacial striations are left when large boulders are dragged beneath glaciers. As they drag, they scratch the underlying surface creating grooves parallel to the direction of travel of the glacier.
- However, these striations are recorded in areas that are too warm to have glaciers now.
- Aligning the striations show that they could have only emanated from a single point.
GEOLOGICAL: Explain jigsaw fit evidence.
There is a similarity in the outline of Eastern South America and West Africa, the best fit obtained if the coastlines are matched at a depth below current sea levels at 1000m.
Any area with gaps and overlays can be explained by factors such as coastal erosion and deposition, eustatic or isostatic changes since continental separation.
GEOLOGICAL: Explain Fold Mountains
