Sea level the warmer water expands. For at least the last 100 years, sea level has been rising at an average rate of about per year. Most of this rise can be attributed to the increase in temperature of the sea and the resulting slight thermal expansion of the upper of sea water. Additional contributions, as much as one-quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human uses. Pilots can estimate height above sea level with an altimeter set to a defined barometric pressure.
Earth and water BC. In the 6th book, Darius sent heralds throughout Hellas bidding them demand "earth and water" for the king (Hdt. 6.48). There were not many city-states that refused. In Book 7, he recounts that when the Persians sent envoys to the Spartans and to the Athenians demanding the traditional symbol of surrender, an offering of soil and water, the Spartans threw them into a well and the Athenians threw them into a gorge, suggesting that upon their arrival at the bottom, they could "Dig it out for yourselves." The demand for "earth and water" symbolized that those surrendering to Persians