Final answer:
An ice sheet is an extensive mass of ice covering continents, like the one over Antarctica, with significant geological impact. These ice sheets shape the land beneath them and can affect sea levels if thawed.
Step-by-step explanation:
An extensive, continuous mass of ice covering a continental scale area is known as an ice sheet. These colossal ice masses, such as the one enveloping Antarctica, are not only monumental in size but also significant in their impact on the Earth's geology and ecosystems. Ice sheets are dynamic entities, slowly flowing like rivers of ice, albeit at a much slower rate. Through this process, they erode and transport sediment, revealing much about past climate conditions and the extent of ice coverage during different geologic periods.
One of the most notable characteristics of ice sheets is their ability to shape the land beneath them. As they advance and retreat in repeated glacial cycles, they leave behind distinct geological features such as glacial valleys and glacial troughs, which can become bodies of water when the ice recedes. For example, some of these troughs, which are found along coastlines, have become filled with a mixture of fresh water and seawater.
Considering the massive scale of ice sheets, if all the ice were to melt, it would not only contribute to a rise in sea levels but also relieve the weight on continental crust, possibly leading to 'isostatic rebound', where the land rises as a result of the reduction in pressure. This potential for significant geographic transformation is a subject of study for scientists exploring past and future climatic changes on our planet.