Some eight letter words from the ocean are:
The word you're looking for is "eider." Eiders are large sea ducks primarily found in the Northern Hemisphere.
pea, sea, tea
pirate
Ocean
Sea?
at sea
The answer to the riddle is the letter "E." It is found in the word "earth," appears twice in the word "heaven," is present in the word "year," and is in the middle of the word "sea."
port
bed
sea
Ern
sea