Final answer:
Major ocean floor features include mid-ocean ridges, deep-sea trenches, and abyssal plains; mid-ocean ridges signify the youngest crust due to seafloor spreading, deep-sea trenches represent the oldest crust being subducted, and abyssal plains consist of old, sediment-covered crust.
Step-by-step explanation:
The major features of the ocean floor such as mid-ocean ridges, deep-sea trenches, and abyssal plains signify different stages in the oceanic lithosphere's lifecycle and are vital to understanding plate tectonics. Mid-ocean ridges are underwater mountain systems formed by plate tectonics and are characterized by seafloor spreading. Here, magma rises from beneath the Earth's surface, hardening to form new crust. Due to this continuous process, mid-ocean ridges are associated with the youngest sections of the ocean floor.
Deep-sea trenches are the deepest parts of the ocean basins and represent areas where one tectonic plate is subducting under another, leading to the oldest oceanic crust being pushed deep into the mantle. Abyssal plains are extremely flat areas of the ocean floor found at great depths, and they are among the most extensive landforms on Earth. These plains are covered with thick sediments, which bury the topography of the underlying ocean crust, and tend to be older than the newly formed crust at the ridges due to the gradual accumulation of sediments.
By comparing the seafloor ages between the mid-Atlantic Ocean and the Pacific Ocean, off the coast of South America, it can be determined which spreading ridge is spreading faster. The age of the seafloor can be used to determine the rate of spreading, with the youngest crust found nearest to the ridges, indicating more rapid spreading. In summary, mid-ocean ridges are indicative of new crust being formed, deep-sea trenches represent the destruction of old crust, and abyssal plains are the resting place for sediment-covered ancient crust.