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The earth’s crust is broken into separate pieces called tectonic plates (Fig. 7.14). Recall that the crust is the solid, rocky, outer shell of the planet. It is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. Both types of crust rest atop solid, upper mantle material. The upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar.
Each tectonic plate is free-floating and can move independently. Earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines. The term fault is used to describe the boundary between tectonic plates. Most of the earthquakes and volcanoes around the Pacific ocean basin—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. Other observable results of short-term plate movement include the gradual widening of the Great Rift lakes in eastern Africa and the rising of the Himalayan Mountain range. The motion of plates can be described in four general patterns:
<p><strong>Fig 7.15.</strong> Diagram of the motion of plates</p>
Collision: when two continental plates are shoved together
Subduction: when one plate plunges beneath another (Fig. 7.15)
Spreading: when two plates are pushed apart (Fig. 7.15)
Transform faulting: when two plates slide past each othe
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Some common insulators include wood, plastic, glass, porcelain and Styrofoam
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The cell membrane is the semipermeable membrane of a cell that surrounds and encloses its contents of cytoplasm and nucleoplasm.
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B) ecological succession
Explanation:
The analogy given in this question describes ECOLOGICAL SUCCESSION, which is the series of changes that an ecosystem undergoes over a period of time. Ecological succession is of two types viz: Primary succession and Secondary succession.
Primary succession involves the series of changes that occurs on a new habitat that has never been previously colonized. This is the case of the colonization of bare rocks with no plant life by LICHENS. The action of the lichen, which involves secretion of acids that disintegrates the rocks into soil, paves way for the colonization of that area by new species.
Lichens, via the role they play in primary succession by helping alter a barren area into a fertile one that accommodates other organisms, makes them be regarded as PIONEERS of primary succession.
