Saturday, July 7, 2012

The Nature of Sea Levels

Sea Surface by Petr Kratochvil
Sea level is the average height of the ocean's surface. Sea levels have fluctuated over time.


Mean Sea Level is a way to express the elevation of the sea with wave motion and tide changes averaged out.

Geologic observation and artifacts narrate the story of the oceans.

Constant Change

Sea level fluctuations are preserved in the geologic record.

Sedimentary and fossil records are often the key to estimating historic sea levels. Coral reefs are also accurate markers because they grow just below the prevailing sea level of the time.

There is sedimentary and fossil evidence that sea level was more than 21 meters (70 ft) higher 400,000 years ago than it is today:
...sedimentary and fossil evidence in the walls of a limestone quarry in Bermuda that documents a rise in sea level during an interglacial period of the Middle Pleistocene in excess of 21 meters above its current level. ~ Dramatic Rise In Sea Level And Its Broad Ramifications Uncovered

Ocean and Continents

Western Interior Seaway
The notion of the familiar borders between oceans and continents seems static within the time scale of a human lifetime. Over a geologic timescale, oceans and continents appear ever-changing.
Even Castles made of sand, fall into the sea, eventually.
Jimi Hendrix
The Western Interior Seaway was an inland sea that divided North American into two landmasses during the Mid-to-Late Cretaceous period. Vast carbonate deposits indicate the Seaway was warm and tropical.

The shallow Western Interior Seaway supported abundant marine life and early birds.