CHAPTER IN PERSPECTIVE
Chapter 1: Origins

In this chapter you learned that Earth is a water planet, possibly one of few in the galaxy. An ocean covering 71% of its surface has greatly influenced its rocky crust and atmosphere. The ocean dominates Earth, and the average depth of the ocean is about 4½ times the average height of the continents above sea level. Life on Earth almost certainly evolved in the ocean; the cells of all life forms are still bathed in salty fluids. We study our planet using the scientific method, a systematic process of asking and answering questions about the natural world. Marine science applies the scientific method to the ocean, the planet it is part of, and the living organisms dependent on the ocean. Most of the atoms that make up Earth and its inhabitants were formed within stars. Stars form in the dusty spiral arms of galaxies and spend their lives changing hydrogen and helium to heavier elements. As they die, some stars eject these elements into space by cataclysmic explosions. The sun and the planets, including Earth, probably condensed from a cloud of dust and gas enriched by the recycled remnants of exploded stars. Earth formed by the accretion of cold particles about 4.6 billion years ago. Heat from infalling debris and radioactive decay partially melted the planet, and density stratification occurred as heavy materials sank to its center and lighter materials migrated toward the surface. Our moon was formed by debris ejected when a planetary body somewhat larger than Mars smashed into Earth. The ocean formed later, as water vapor trapped in Earth’s outer layers escaped to the surface through volcanic activity during the planet’s youth. Comets may also have brought some water to Earth. Life originated in the ocean very soon after its formation—life and Earth have grown old together. We know of no other planet with a similar ocean, but water is abundant in interstellar clouds and other water planets are not impossible to imagine.

In the next chapter you will learn that science and exploration have gone hand in hand. Voyaging for necessity evolved into voyaging for scientific and geographical discovery. The transition to scientific oceanography was complete when the Challenger Report was completed in 1895. The rise of the great oceanographic institutions quickly followed, and those institutions and their funding agencies today mark our path into the future.