Rock can form in several ways: molten rock can cool to become igneous rock, both at and beneath the Earth’s surface; sediments weathered from rocks can settle out of water or wind to form layers that, when compacted turn into sedimentary rock; and finally, rocks that already exist can undergo changes as a result of intense pressure and high temperatures to become metamorphic rock. The processes of rock formation are not part of children’s everyday experience, and, with the exception of lava cooling to form rock, take place over immense time periods. It is challenging for children to be able to understand or visualize what is unseen.Hide Response

Most sedimentary rocks form through deposition, recrystallization, and cementation. Gravity causes sediment to settle to the bottom of a body of water. These sediments gradually accumulate, forming layers that compact the layers of sediments below. Water that surrounds the sediment contains dissolved minerals that recrystallize and cement the grains of the sediment together, forming rock. Children’s experiences are likely to be limited to sediments and sediment transport that is associated with bodies of water, like streams and ponds. It may therefore be difficult for them to comprehend the transition from sediment to sedimentary rock. Hide Response

The rock cycle is a set of processes that, over immense periods of time, convert one type of rock into another. During this process, rocks are formed and destroyed. Children perceive rock as immutable, and often believe that rocks have always been there and do not change. Also, children's experience with the process of melting does not lead them to believe that rocks can melt. Hide Response

With the exception of volcanic rocks, the time it takes rock to form is on the order of millions of years. Rocks of varying ages can be found today. Many children believe that dirt or sand can harden into rock, which can give rise to the idea of rock being formed in a few years. Other children may observe rock to be unchanging, which might lead them to reason that it’s permanent. Children’s ability to perceive time on a geologic scale limited—younger children's perception of the difference between "a few years" and "since the beginning of the Earth" is fuzzy at best. Hide Response

Rocks are not necessarily formed at their current location. For example, rocks can be formed underground and then pushed or folded to a new location. Magma can travel from beneath the Earth’s surface, erupt through a volcano as lava, and travel some distance on the Earth’s surface before it hardens into rock. Smaller rock pieces that are weathered from larger rock masses can be transported over great distances by wind, water, or ice. Few children, however, have an opportunity to observe any of these phenomena. Hide Response