It undergoes a transition from the olivine structure to the spinel structure. These transitions account for the discontinuous increase of the Earth's mantle as observed by seismic instruments.
6. How do mountains in the ocean basin differ from those on land?
Mountains in the ocean basins are perpetually being "recycled" through subduction zones. Therefore, the rock that they are made of differs in composition to mountains on land because of their younger age and mineral composition. Many of the mountains on land were created through uplifts in the crust, where rock from the crust was pushed upward and folded over time and time again. These types of rock have more metamorphic qualities while the ocean-bottom mountains tend to be more volcanic in nature and are more igneous. Also, the oceanic crust is made of basalt vs. The continental crust made of granite.
7. Why are continents so much higher than ocean basins?
The continents are higher than the ocean basins because of their crust density. The oceanic crust is mainly made up of basalt, which has high iron and nickel content and is therefore thinner and denser. The continental crust is thicker because it is made up of mostly granite which has high levels of silicate and aluminum. The continental crust is of lower density.
8. Why are some mountains belts so much higher than others?
Some mountain belts are much higher than others because of the forces that created them. The Himalayas, Earth's highest mountain range, is a product of plates...
The mountains grow each year because as the plates push together, parts of the crust are lifted up over others. As the wrinkles increase, the mountains are pushed higher and higher. Other mountain ranges are formed through smaller crustal impacts or even through subduction zones. Hawaii is a great example of a mountain range being created near a subduction zone.
9. How does the average composition of continents differ from that of oceans?
The average composition of continents differs from that of the oceans in that continents are far less dense being made out of mostly granite and granitic compounds. This is also why they tend to be thicker. The ocean bottom is made up of mostly iron and nickel-based rocks that are igneous in nature and far denser.
10. How do passive continental margins differ from active continental margins?
Active continental margins are those margins found on the leading edge of a continent where it is colliding with an ocean plate. These active margins are more active geologically as well as seismologically. They are also the sight of formation for new igneous rock. Mountains and other geologic features are more common in the active margins. Passive continental margins are the margins where no collision or subduction is taking place. These margins are weathered down by erosion and other natural forces since they remain little changed due to the lack of activity. This leads to lots of flat land areas protruding from these areas.
