Earth’s Shape, Size and Internal Structure Inside the Earth Earth’s Shape, Size and Internal Structure

The earth is round. Eratosthenes figured it out in 200 B.C. He calculated that Earth’s circumference was 40,000 km – only off by 8 km!!

Eratosthenes & the Round Earth 7.2o angle at Alexandria No angle at Syene (on the Tropic of Cancer) Central angle is 7.2o (1/50th of 360o). A soldier paced off distance from Alexandria to Syene (5,000 stadia = 800 km).

Eratosthenes & the Round Earth (5,000 stadia = 800 km). Multiply X 50, you get the circumference of the Earth: 800 km X 50 = 40,000 km Actual diameter of the Earth (pole to pole) = 40,008 km. Incredibly close for this method of measuring!

The earth is sort of round – Oblate Spheroid Due to its rotation, Earth bulges slightly at the equator (about 0.17 % bigger) and is slightly flattened at the poles. It is an oblate spheroid.

The earth is sort of round – Oblate Spheroid Equatorial diameter is just 0.17 % bigger than the Polar diameter.

The earth is tilted at a 22 ½ o angle.

4 Layers of the Earth Scale Crust 0 – 70 km thick 2,885 km thick

} 2 Types of Crust } 1) Oceanic Crust Continental Crust 5 – 10 km } 20 – 70 km

Two Essentially Different Rock Types Continental Crust- Granite } Two Essentially Different Rock Types Continental Crust- Granite Oceanic Crust - Basalt

The Mantle – Thickest Single Layer Lithosphere – Crust and Uppermost mantle (Solid, Rigid, Brittle) Asthenosphere – Crust and uppermost mantle (Plastic, weak, flows like Silly Putty) Mesosphere - Lower Mantle (Solid Again)

The “Moho” The Mohorovičić discontinuity (“Moho” for short) is a sudden, sharp boundary between the crust and the upper mantle. Increase in P wave velocity is due to a sudden increase in density of the rocks.

Layers of the Mantle Lithosphere – Rigid and Brittle (partly crust) Asthenosphere – Plastic and flowing Mesosphere (lower mantle) – Solid Again

Iron Silicate Minerals Rocks of the Mantle Olivine Peridotite – Iron Silicate Minerals Magnetite – Iron Oxide

Inner and Outer Cores Outer Core: Liquid Iron and Nickel Hot, but not as hot as the inner core 2,270 km thick

Core – Mantle Boundary Huge mountainous “anti-continents” of solid mantle protrude downward into the “anti-oceans” of the liquid iron core.

The Two Cores Outer Core – Hot liquid Iron and Nickel with lumpy core /mantle boundary Inner Core – Even hotter but crystalline Iron and Nickel

Core Materials The inner core is thought to be made of crystalline iron similar to the type we find in iron meteorites. These distinctive crystal patterns are called Widmanstatten lines.

Thicknesses of the 4 Layers Crust 0 – 65 km thick 2,885 km thick 2,900 km 2,270 km thick 5,100 km 1,216 km thick Scale 6,400 km