Relief of Oceans:
The relief of oceans refers to the various features and formations present on the ocean floor. It includes the underwater mountains, valleys, plateaus, and trenches that make up the topography of the oceanic landscape. Understanding the relief of oceans is crucial in studying and exploring the Earth's marine environments.

Structure and Composition:
The structure and composition of the relief of oceans differ significantly from those of land surfaces. These differences can be observed in terms of their formation, composition, and processes shaping them.

Formation:
1. Tectonic Activity: The relief of oceans is primarily formed due to tectonic activity. The Earth's crust is divided into several large and small tectonic plates. The movement and interaction of these plates create various oceanic features. For example, the mid-oceanic ridges are formed when two plates diverge, and magma rises to fill the gap.
2. Volcanic Activity: Volcanoes are common in the oceanic realm, especially along the mid-oceanic ridges. These volcanic activities contribute to the formation of underwater mountains and plateaus. The eruptions release magma, which solidifies to form new oceanic crust.

Composition:
1. Basaltic Rocks: The composition of the oceanic relief is primarily basaltic rocks, which are rich in iron and magnesium. These rocks are denser and have a higher specific gravity compared to the continental rocks, which are mainly granite.
2. Sediments: The ocean floor is covered with various types of sediments, including clay, silt, sand, and gravel. These sediments are derived from weathering and erosion of land surfaces, as well as from marine organisms.

Processes Shaping the Relief:
1. Erosion and Deposition: Ocean currents and waves play a significant role in shaping the relief of oceans. They erode the coastline, transport sediment, and deposit them in various areas. This process contributes to the formation of continental shelves, submarine canyons, and deltas.
2. Subduction and Trench Formation: When two tectonic plates converge, one plate is usually forced beneath the other in a process called subduction. This subduction leads to the formation of deep ocean trenches, such as the Mariana Trench, which is the deepest part of the world's oceans.

In conclusion, the relief of oceans differs from land surfaces in terms of its formation, composition, and processes shaping it. Tectonic and volcanic activities play a crucial role in the formation of underwater features, which are primarily composed of basaltic rocks. Oceanic relief is also influenced by erosion, deposition, and subduction processes, creating a diverse and unique landscape beneath the ocean's surface.