A semi-comet?

Photographs, taken from Earth-orbiting satellites, show small, ice-filled comets striking Earth’s upper atmosphere at at average rate of one every three seconds. Each comet adds 20-40 tons of water to the Earth’s atmosphere. If this influx began when evolutionists say the Earth started to evolve, all our oceans would have come from small comets. Actually, impact rates were undoubtedly greater in the past, because the planets have swept many of these comets from the solar system....Because comets contain water twice as rich in heavy hydrogen as our oceans, most of Earth’s water could not have come from comets, large or small, even if comets have bombarded Earth for billions of years. 

                  -----Walt Brown, In The Beginning, Center for Scientific Creation, seventh edition, 2001, pp. 34, 196