Abstract
The well-known “black smoker” hydrothermal systems occur at ocean spreading centers, which are primarily composed of basalt. High temperature (200° – 400°C) fluids in these systems pass through the basalt, where they become both acidic (pH 3-5) and rich in metals. As they emerge on the seabed, they precipitate metal-rich chimneys. Fluids that interact with mantle rocks have fundamentally different chemistries. These lesser-known hydrothermal systems occur within serpentinite. Serpentine systems form as rocks found deep in the earth (peridotite) are uplifted to the seabed and exposed to seawater. Here chemical reactions at lower temperatures (100 – 200°C) occur that convert primary Fe- and Mg-bearing minerals (olivine) to serpentine, releasing hydrogen (H2) and producing alkaline (pH = 9-10) fluids. These conditions allow simple carbon molecules to be converted to more complex organic molecules including, potentially, amino acids, without the assistance of living organisms. Once formed, these molecules slowly degrade. A fundamental question regarding serpentinite-hosted systems is whether the molecules can be exported to the seabed before they are destroyed. In this first investigation of radium isotopes in a serpentinite-hosted system, vent fluids were discovered to contain 10 –100 times greater activities of 223Ra (half-life = 11.4 d) than observed in high temperature basalt-hosted systems. The 223Ra/226Ra activity ratios ranging from 9 – 109. These findings require fluid circulation times within the serpentine of less than 2 years and perhaps as low as 0.5 years, likely short enough to allow complex organic molecules to be exported into overlying ocean waters. Some scientists think such sites may be conducive to the development of life on earth and perhaps other planets and moons.
Biography
Willard S. Moore received his doctorate degree in earth and space sciences from State University of NY. He has served on the National Advisory Council/National Research Council, the international commission on Marine science (SCOR), and the Groundwater Discharge Working Group. Professor emeritus Willard Moore was elected as a Fellow of American Geophysical Union in 2006 and Fellow of the American Association for the Advancement of Science in 2014.
The primary research of his laboratory is based on the use of natural radioisotopes as tracers of geological and oceanographic processes. By measuring precisely radioisotopes that result from the decay of uranium and thorium in the environment, his group investigates such diverse topics as interactions of river water and sediments with sea water; flow of ground water through salt marshes; the mixing rate of the ocean; hydrothermal processes at ocean spreading centers; the internal structure of minerals; the ages, rates, and processes of formation of manganese nodules; the rate of growth of corals; and sea level changes.
