Earth Science Literacy InitiativeDraft Document – October, 2008 Big Idea #1: Earth is 4.6 billion years old and the rock record contains its history. Supporting Concepts 1.1 Our Earth and Solar System formed from a vast cloud of gas and dust 4.6 billion years ago. This age is determined using the decay rates of radioactive elements contained in Earth’s oldest known rocks, meteorites and Moon rocks. 1.2 Earth formed from the gravity-driven accumulation of dust and gas and the multiple collisions of smaller planetary bodies. During formation, iron sank out of the mostly-molten Earth to form the core. The surrounding mantle eventually cooled to form rock, which is made of minerals. Minerals are composed of elements. 1.3 The Moon formed from the ejected material of an early collision between Earth and a Mars-sized body. Earth and the Moon have continuously cooled since this time. 1.4 No surface rock remains from the violent first few hundred million years of Earth’s history due to frequent impacts of smaller planetary bodies and vigorous churning of the mantle. Studying other planets helps Earth scientists learn about this early time. 1.5 Earth’s ocean, atmosphere and crust began to form more than 4 billion years ago from the rise of lighter materials out of the underlying mantle. Continental crust persists at Earth’s surface and can be billions of years old, whereas oceanic crust continuously forms and recycles back into the mantle. No part of the modern oceanic crust is older than 200 million years. 1.6 To reconstruct Earth’s history, Earth scientists use the structure and sequence of rocks, sediments and fossils, as well as the chemical and physical properties of those materials. Decay rates of radioactive elements are the primary means of obtaining absolute ages of rocks. 1.7 One way Earth scientists understand Earth’s history is by observing and interpreting processes at work today. This understanding of the past and present is an important guide for forecasting Earth’s future. 1.8 Evidence for life’s origin and history is preserved in the rock record. Fossils indicate that life began with single-celled organisms over 3 billion years ago, and that humans (Homo sapiens) have existed for only a very small fraction (about 0.004%) of Earth’s history. 1.9 Over Earth’s vast history, slowly acting processes have produced enormous changes: supercontinents form and break apart, ocean basins open and close, living species evolve and go extinct, ice sheets advance over lands and melt away, seas flood the continents and recede, and the compositions of the atmosphere and oceans continually change.
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