Final answer:
Most sedimentary rocks on continents were indeed formed underwater in various depositional environments. Fossils are well-preserved in areas where rapid burial and low oxygen levels occur, particularly in marine settings. Geologists use features such as rock color to help identify the depositional environment, which aids in understanding Earth's history.
Step-by-step explanation:
It is true that most sedimentary rocks found on continents were formed underwater. Sedimentary rocks form in various depositional environments, which are categorized into continental, marine, and transitional zones. On continents, sedimentary layers are deposited in rivers, lakes, and deserts, while in marine settings, they accumulate in environments like shallow seas and deep ocean floors. Transitional environments, such as coastal and tidal areas, also contribute to sediment deposition.
Fossils are best preserved in depositional environments that provide rapid burial and low oxygen conditions, which limits decay and scavenging. Consequently, marine environments such as shallow seas and lagoons, where there is a high rate of sedimentation, and anoxic bottom waters, are particularly good at preserving fossils. Similarly, lakes and peat swamps in continental settings can also effectively preserve fossils.
Examples of sedimentary rocks and fossils reveal histories of past environments, such as the presence of oysters indicating a marine environment, or the distinct layers of sediments at Hartland Quay suggesting deposition in a shallow sea during the Carboniferous period. The variation in rock color, from red indicating oxygen-rich environments to black suggesting anoxic conditions, further assists in reconstructing depositional settings and their respective histories.