Structure of earth
The shape of the earth is somehow spherical but flattened at the poles and is slightly flattened at the equator. Earth is made of three layers which are
- The crust (outer layer of the earth): the crust is made up of granite, basalt, gabbro and other types of rock.
- The molten mantle: the molten mantle is located below the crust. It is made up of silica and metal rich minerals.
- The core: it consists of two layers which are:
- The outer core; they consists mostly of liquid
- The inner core; they consists mostly of iron
Source: www.hyperphysics.com
Source: www.worldatlast.com
The theory of plate tectonics explains what earth crust is all about; it explains the follow:
- How major landform are created
- How the seafloor spreads
- How the continents move
Note that at the boundaries between plates, major lands are being formed such as mountain ranges, volcanoes, ocean trenches and mid ocean ridges form and earthquakes occur.
There are three types of plate boundaries, or margins
- In a constructive margin; two plates are moving apart and new crust is forming.
- In a conservative margin; two plates are sliding by one another, here no crust is created or destroyed.
- In a destructive margin; here when two plates that contains two continental crusts collide, the crust crumbles as a result of the collision to form mountain ranges.
Source: www.oregongeology.org
Questions
- According to the passage the earth is slightly ………… and ……..At the pole?
A. Curved and straighten
B. Bend and flattened
C. Spherical and bulging
D. Spherical and flattened
Ans= D
2. From the options below which give better explanation or shows evidence that present day continents were once large continent?
A. The west coast of Africa seems to fit into the east coast of the Americans
B. Australia is a large continent sized island.
C. Australia and Antarctica are located in the southern hemisphere.
D. Eurasia is the largest land mass on earth
Ans= A
3. Which of the following best explained the theory of plate tectonics?
A. Changes in earth’s mantle
B. Changes in earth’s crust
C. Why there is extreme heat and pressure in earth’s core
D. Changes in the composition of earth’s layers
Ans= B
- List the three types of boundaries/margins?
Ans=
I. Destructive margin
II. Conservative margin
III. Constructive margin
5. From the content above the earth is made up of three layers, mention them?
Ans=
I. The core
II. The mantle
III. The crust