page_title: Sea level
section_title: Long-term changes in sea level
hierarchical_section_title: Sea level / Long-term changes in sea level
context_page_description: The sea level is the average height of the ocean. The word 'average' must be used because the height of the sea changes with the tides. The height of mountains, countries, and so on, is almost always given as "above sea level".
context_section_description: In Earth's long history, the continents and sea floor have changed due to plate tectonics. This affects global sea level because it alters the depths of various ocean basins, and also changes the distribution of glaciers. 
  Over most of geologic time, the long-term mean sea level has been higher than today (see graph). Only at the Permian-Triassic boundary ~250 million years ago was the long-term mean sea level lower than today. This included the Permian–Triassic extinction event, though this may not be relevant to the concept of sea level.
  Long term changes in the mean sea level are the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term.
caption: Sea level change since the end of the last ice age. Changes shown in metres
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