How did life begin? How does Earth’s interior work, and how does it affect the surface?

2. What happened during Earth’s “dark age” the irst 500 million years? It is now believed that during Earth’s forma- tion, 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 irst 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 condi- tions became hospitable enough to support life. Some clues from Earth’s oldest minerals zir- cons, 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 modiica- tion 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, and in what form did life irst appear? The origin of life is one of the most intriguing, dificult, and endur- ing questions in science. Scientists have toiled to create life from sparks and gasses in the laboratory to illuminate how life irst formed in Earth’s early conditions. But even pinning down what those early conditions were remains an elusive goal. From what materials did life originate? Did life, as Darwin speculated, originate in a “warm little pond,” perhaps a tidal pool repeatedly dried and refreshed? Or might life be rooted among hydrother- mal vents? Could life’s origins even lie beyond Earth? Developing an accurate picture of the physical environments and the chemical building blocks avail- able to early life is a critical Earth science challenge. Clues to shed light on these mysteries stem largely from investigations of Earth’s ancient rocks and min- erals—the only remaining evidence of the time when Earth’s life irst emerged. Earth’s Interior 4. How does Earth’s interior work, and how does it affect the surface? As planets age and cool off, their internal and surface processes gradually change. Manifestations of changes within Earth’s interior—such as the develop- ment of mountains and volcanoes—have a huge inlu- ence on the nature of Earth’s surface and atmosphere. Scientists know that much of the rock in the Earth’s mantle the thick layer between the core and crust, which is under extreme pressure and very high temperature, behaves like a viscous liquid. This vast interior, however, is largely inaccessible to direct study. For over a century, seismic wave, geomagnetic, and gravity measurements made at the surface have been improving understanding of Earth’s internal structure. Despite continuing advances, however, scientists are only beginning to explore the connec- tions between Earth’s core, magnetic ield, mantle, and surface and to investigate why Earth differs from other planets, or how it may change in the future. 5. Why does Earth have plate tectonics and continents?