Final answer:
Transgression occurs when sea levels rise and cover previously exposed land, while regression is when sea levels fall and exposed seabeds become land. Sea level rise is mainly due to global warming causing ice melt and ocean expansion. Sea level fall is less common but can occur due to ice sheet formation or tectonic activity.
Step-by-step explanation:
A transgression is a geological process during which sea levels rise and flood previously exposed land, leading to areas of land becoming submerged under sea level. This process is illustrated by sediment deposits that stack toward the coastline in a pattern referred to as onlapping. On the other hand, a regression is the opposite geological occurrence where the sea level falls, and areas of previously submerged seafloor are exposed above sea level. These sequences are crucial in lithostratigraphy and sequence stratigraphy for decoding Earth's history through rock layers.
World-wide sea level rise can be primarily attributed to two factors: the melting of land-based ice, such as glaciers and ice sheets, and the thermal expansion of seawater as it warms. The rise in global temperature, typically caused by climate change and global warming, is a substantial driver of both these factors. In contrast, sea level fall, although less common in the current geological epoch, can happen due to the formation of large ice sheets that lock up vast quantities of water, thus lowering global sea levels. Additionally, geological events such as tectonic activity can influence local sea levels, though typically not on a world-wide scale.
Tides, which are alternate rising and falling of sea level, are caused by variations in the Moon's gravitational pull on the Earth, but these are short-term changes and do not contribute to long-term sea level rise or fall.