Hi Ned. Thanks for commenting. Sea levels have indeed risen and fallen on the order of 400 feet due to glacial and interglacial cycles throughout the past 2 million years. However, research shows that sea levels changed little from AD 0 until 1900 but since 1900 have risen at a rate of 0.04 to 0.1 inches per year and that this is a significantly larger rate than the sea-level rise averaged over the last several thousand years.
The two main causes of global sea-level rise are
(1) thermal expansion caused by the warming of the oceans and (2) the melting of glaciers and ice caps on land.

See this NOAA site for more details on sea level rise and its causes. http://oceanservice.noaa.gov/facts/sealevel.html
See this NOAA site to track global sea level, sea ice, temperature, carbon dioxide concentrations and more. http://climate.nasa.gov/

How Do They Form?

Marine terraces can be found in many places around the globe but just the right conditions must be present for them to form. These are:

Slow and steady tectonic uplift (rates of about 0.02 inches per year)
Repeating cycles of rising and falling sea level (rise and fall of up to 400 feet!)
Just the right rate of erosion for a wave cut platform to form and a sea-cliff to be preserved

To understand how marine terraces are created, begin by thinking about the beaches of today. Each of the terraces you see once looked like a modern beach.
Schematic showing how a modern beach platform evolves into a marine terrace. Figure from a 2001 USGS paper by Gerald Webber and Alan Allwardt (listed at Bottom).