Welcome to Geology at Miramar

Chapter 1- Introduction

The Nebular Hypothesis The solar system began as dust and gas (from an exploding supernova?) collapsed due to gravity. The nebula contracted into a rotating disk. Repeated collisions of rocky and metallic material coalesced into asteroid, then planet-sized bodies. Age of the earth and solar system about 4.5 billion years (4500 million years). Heating and subsequent cooling of Earth caused heavy metals to sink to the interior and lighter elements to rise to the surface.

Earth’s internal structure Earth’s internal layers can be defined by Chemical composition Physical properties(molten, solid) Layers defined by composition Crust: silica (SiO2)-rich composition Mantle: silica and iron composition Core: iron and nickel composition

Earth’s internal structure Figure 1.13

Earth’s layers by physical properties In the crust and upper mantle: Lithosphere – rigid solid which make up the tectonic plates, includes both crust and mantle Asthenosphere – partially molten “weak” layer Lower mantle (mesosphere) mostly solid Core outer core (molten inner core (solid)

Earth’s internal structure Figure 1.13

Continental and Ocean Crust Continental crust is thicker (average 35-40 km) older (up to 4 billion years old) and is generally less dense than ocean crust. Ocean crust averages 5-7 km thick, is 200 million years old or younger and is mostly composed of dark volcanic rock basalt.

Age of the Ocean Floor

Plate Tectonics: the new paradigm From left to right: Transform boundary (conservative) Convergent boundary (destructive) Divergent boundary (constructive)