In case you needed a reminder that much of the territory occupied by Pleistocene humans is now beneath the waves, just take a look at this press release from the British archaeology company Wessex Archaeology:
An amazing collection of 28 flint hand-axes, dated by archaeologists to be around 100,000 years-old, have been unearthed in gravel from a licensed marine aggregate dredging area 13km off Great Yarmouth.
The find was made by a Dutch amateur archaeologist, Jan Meulmeester, who regularly searches for mammoth bones and fossils in marine sand and gravel delivered by British construction materials supplier Hanson to a Dutch wharf at Flushing, near Antwerp, south west Netherlands.
The axes show that deep in the Ice Age, mammoth hunters roamed across land that is now submerged beneath the sea. These are the finest hand-axes that experts are certain come from English waters, although there have been a few finds on beaches, for example at Pakefield in Suffolk.
As a result of the find, they moved the dredging operation to conform with regulations -- I suppose to preserve the site in case the sea level falls!
It seems to me that these are likely to predate 100,000 years ago, but no date is really possible given the circumstances.
This isn't the first such find. Werz and Flemming (2001) reported the separate discoveries of three quartzite bifaces during shipwreck archaeology in Table Bay, South Africa. Again these are undated but probably precede 300,000 years ago. Finds of artifacts from the later stages of the Paleolithic have been more common.
Werz BEJS, Flemming NC. 2001. Discovery in Table Bay of the oldest handaxes yet found underwater demonstrates preservation of hominid artefacts on the continental shelf. S Afr J Sci 97:183-185.