Contributions to our knowledge of Earth, and thus of our origins. An argument used to deny the existence of the small comets relies upon scientific dogmas which explain all facets of our planet and our origins with absolutely no need for a role for the small comets. But over the past ten years or so our advances in technology have revealed exciting new results which are beyond the reach of the dogmas. The discovery of the small comets is one such example of the advancement of our scientific frontiers. We summarize here several of the important implications of this swarm of small, dark comets which are present in the vicinity of our planet. The origins of our oceans always have been a fascinating mystery. In his classic paper of 1951 William Rubey noted that an inventory of Earth's water gave the following results. Earth's Water Inventory (in units of 100 million million tons) In present hydrosphere, atmosphere and biosphere 14,600 Buried in ancient rocks 2,100 Total 16,700 This is to be compared with the supply by weathering of rocks 130 Then the water unaccounted for is a remarkable 16,600 Rubey was puzzled by the large amount of water which was unaccounted for. Even at the time of writing his seminal paper he queried astronomers as to whether it was possible that this water was being supplied by an infall of objects from interplanetary space. The responses of astronomers were negative. The mystery was not resolved. But our knowledge of the geological dynamics of Earth is currently expanding at a rapid rate. Large amounts of water are now believed to be lost as subduction of continental plates carries oceanic water under the surface. This scenario is depicted in Figure 12 [above]. This water was thought to be recycled to the surface by outflow of gases from volcanic activity. This was a natural suggestion in consideration of the dramatic activity of volcanoes. A picture of such a volcano is shown in Figure 13 [right]. This is Paricutin which was born in a Mexican corn field in 1943. In a recent classic paper of 1999 David Deming reports on the amount of water which is returned to the Earth's surface by volcanic activity and finds that: "The losses of surface water due to subduction into the mantle are greater by factors of 7 to 20 than the supply given by volcanic activity." "The rate of a cosmic influx of water to compensate for the water loss to the mantle is similar to that derived by Frank and Sigwarth [1993] from observations of small comets." The significance of the small comets is obvious: our Earth would be dry and barren without an extraterrestrial influx of water. But a further conclusion in Deming's paper is unsettling. "Life on Earth may be balanced precariously between cosmic processes which deliver an intermittent stream of life-sustaining volatiles from the outer solar system or beyond, and biological and tectonic processes which remove these same volatiles from the atmosphere by sequestering water and carbon in the crust and mantle." [Next Page] Home Presidential Lecture, Part 1 2 3 4 5 6 7 8 9