Origin and Evolution of Earth

Earth is an active place. Earthquakes rip along plate boundaries, volcanoes spew fountains of molten lava, and mountain ranges and seabed are constantly created and destroyed. Earth scientists have long been concerned with deciphering the history—and predicting the future—of this active planet. Over the past four decades, Earth scientists have made great strides in understanding Earth’s workings. Scientists have ever-improving tools to understand how Earth’s internal processes shape the planet’s surface, how life can be sustained over billions of years, and how geological, biological, atmospheric, and oceanic processes interact to produce climate—and climatic change. At the request of the U.S. Department of Energy, National Aeronautics and Space Administration, National Science Foundation, and U.S. Geological Survey, the National Research Council assembled a committee to propose and explore grand questions in Earth science. This report, which is the result of the committee’s deliberations and input solicited from the Earth science community, describes ten “big picture” Earth science issues being pursued today. Answers to these fundamental questions could profoundly improve understanding of the planet on which we live and strategies for managing our environment.

Origins

1.      How did Earth and other planets form?

The Solar System is composed of a set of radically different types of planets and moons— from the gas giants Jupiter, Saturn, Uranus, and Neptune to the rocky inner planets. Centuries of studying Earth, its neighboring planets, and meteorites have enabled the development of models of the birth of the Solar System. Astronomical observations from increasingly powerful telescopes have added a new dimension to these models, as have studies of asteroids, comets, and other planets via spacecraft, as well as geochemical studies of stardust and meteorites. While it is generally agreed that the Sun and planets all coalesced out of the same nebular cloud, little is known about how Earth obtained its particular chemical composition, or why the other planets ended up so different from Earth and from each other. For example, why has Earth, unlike every other planet, retained the unique properties—such as the presence of water—that allow it to support life? New measurements of Solar System bodies and extrasolar planets and objects, will further advance understanding of the origin of Earth and the Solar System.

2.      What happened during Earth’s “dark age” (the first 500 million years)?

It is now believed that during Earth’s formation, a Mars-sized planet collided with it, creating a huge cloud of debris that became Earth’s Moon and releasing so much heat that the entire planet melted. But little is known about how the resulting molten rock evolved during the planet’s infancy into the Earth we know today. The first 500 million years of Earth’s existence, known as the Hadean Eon, is a critical missing link in understanding how the planet’s atmosphere, oceans, and differentiated layers of core, mantle, and outer crust developed. Scientists have almost no idea how fast the surface environment evolved, how the transition took place, or when conditions became hospitable enough to support life. Some clues from Earth’s oldest minerals (zircons), as well as from Earth’s Moon and other planets are allowing a clearer picture of the Hadean Eon to gradually emerge. The future is certain to provide additional breakthroughs. The amount of information that can be extracted from even the tiniest samples of old rocks and minerals is increasing rapidly, and with concerted effort, it is expected that many more ancient rocks and mineral samples will be found.

3.      How did life begin?

In The Origin of Species, Charles Darwin (1859) hypothesized that new species arise by the modification of existing ones—that the raw material of life is life. But somehow and somewhere, the tree of life had to take root from nonliving precursors. When, where,