2.1 Earth A Unique Planet Click for Earth Video Earth: A Unique Planet section 2.1 3 Unique Characteristics 1. liquid water on its surface 2. lots of O2 in the atmosphere 3. can support life Earth Basics · 3rd planet from the sun · 4.6 billion years old · about 70% of the surface covered in H2O (global ocean) · oblate spheroid - slightly flattened sphere bulges at equator pole-to-pole circumference = 40,007 km (24,859 mi) equatorial circumference = 40,074 km (24,900 mi) · relatively smooth surface · diameter = 12,756 km Earth's Interior · direct methods of observation drilling limited to a few km · indirect methods of observation seismic waves - vibrations that travel through Earth helps us determine Earth's interior structure · 3 compositional zones crust, mantle, core · 5 structural zones lithosphere, asthenosphere, mesosphere, outer core, inner core 3 compositional zones · crust - 1% of Earth's mass oceanic crust - under the ocean (5-10 km) continental crust - makes up the continents (15-80 km) part of the lithosphere · mantle - about 2/3 of Earth's mass denser than crust 2,900 km thick lithosphere, asthenosphere, mesosphere · core - about 1/3 of Earth's mass radius 3,500 km outer core and inner core 5 Structural Zones · lithosphere (crust & mantle) "litho" - rock, stone solid, rigid · asthenosphere (mantle) "astheno" - weak, soft solid, plasticity (flows) allows tectonic plates to move · mesosphere (mantle) "meso" - middle solid, strong · outer core (nickel & iron) dense liquid · inner core (nickel & iron) dense, rigid, solid