8th Grade: What Do You Know About Earth Science?

An intrusive rock is formed deep within the Earth's crust. This type of rock is formed when magma cools and solidifies slowly beneath the surface. As the magma cools slowly, it allows for the formation of large mineral crystals within the rock. This is in contrast to extrusive rocks, which are formed when magma cools quickly on the Earth's surface, resulting in smaller mineral crystals or even a glassy texture. Therefore, the word "intrusive" accurately describes an igneous rock that is formed deep within the Earth's crust.

Metamorphic rock is formed by high pressures and temperatures. This process causes the original rock to undergo physical and chemical changes, resulting in a new rock with different mineral composition and texture. Igneous rocks are formed from the solidification of molten material, while sedimentary rocks are formed through the accumulation and compaction of sediments. Therefore, the correct answer is metamorphic, as it specifically describes the rock type formed by high pressures and temperatures.

The rock cycle is a geological process that involves the formation, transformation, and recycling of rocks over time. This process includes different stages such as weathering, erosion, deposition, and lithification. These processes take a significant amount of time to occur, as rocks undergo slow changes over millions of years. Therefore, the correct answer is "millions of years."

Igneous rocks are formed from molten magma that has cooled down and solidified. Magma is molten rock that is found beneath the Earth's surface, and when it cools and solidifies, it forms igneous rocks. These rocks can have a variety of textures and compositions, depending on the cooling rate and the minerals present in the magma. Examples of igneous rocks include granite, basalt, and obsidian.

In a sequence of sedimentary rock layers, the most recently formed rock would be found in the topmost layer. This is because sedimentary rocks are formed over time as layers of sediment accumulate on top of each other. The oldest layers are at the bottom, while the youngest layers are on top. Therefore, the topmost layer would be the most recently formed rock.

Igneous rocks are not made from grains of other rocks that have been cemented together. Igneous rocks are formed from the solidification of molten material, such as lava or magma. This process results in the formation of interlocking crystals, rather than grains of other rocks.

Saltation is not a type of weathering. Weathering refers to the breakdown of rocks and minerals on the Earth's surface, while saltation refers to the process of particles being transported by wind or water in a bouncing or hopping motion. Weathering processes include solution, freeze-thaw, and exfoliation, which involve chemical reactions, physical forces, and expansion/contraction cycles. Saltation, on the other hand, is a transportation process rather than a weathering process.

Igneous rocks are formed through the solidification of molten magma or lava. At destructive plate boundaries, where one plate is being subducted beneath another, magma is often generated as the subducting plate melts. This magma can then rise to the surface and solidify, forming igneous rocks. Similarly, at constructive plate boundaries, where two plates are moving apart, magma can also be generated through the partial melting of the asthenosphere. This magma can then rise to the surface and solidify, forming igneous rocks. Therefore, igneous rocks are most likely to form at both destructive and constructive plate boundaries.

Metamorphic rocks have not been melted. Instead, they are formed through the process of heat and pressure acting on existing rocks, causing them to change their form and structure. This process occurs deep within the Earth's crust, where the temperature and pressure are high enough to alter the minerals and textures of the rocks without melting them completely. Therefore, the statement that metamorphic rocks have been melted is not true.

The correct sequence that describes the formation of a sedimentary rock is suspension, deposition, compaction, cementation. Suspension refers to the process of particles being carried by water or wind. Deposition occurs when these particles settle and accumulate. Compaction is the process of the accumulated particles being compressed due to the weight of overlying layers. Cementation is the final step where minerals dissolved in water fill the spaces between particles, binding them together to form a solid rock.