 The Earth is: The third planet in our Solar System; A terrestrial planet; Composed of a rocky planet with a gaseous atmosphere

The study of the Earth is called Earth Science. Earth Science contains many disciplines including: a. atmospheric sciences b. geology (both physical & historical) c. hydrology d. oceanography e. meteorology & climatology f. astronomy

 The Earth was formed at the same time as the other planets in our Solar System.  The theory as to the formation of our planet is called the Nebular Hypothesis.  This hypothesis says that our solar system evolved from an enormous rotating cloud called the solar nebula.

 The nebula was composed mostly of hydrogen and helium.  About 5 billion years ago, the nebula began to contract.  It assumed a flat, disk shape with the protosun (pre-Sun) at the center.

 Next, the inner planets (terrestrial) begin to form from metallic and rocky clumps.  Then, the larger outer (Jovian) planets began forming from fragments with a high percentage of ices.

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But……. how was the Earth (specifically formed!?!?!?!?!

 As Earth formed, the decay of radioactive elements and heat from high-velocity impacts caused the temperature of the Earth to increase.  Denser materials coalesced or became concentrated toward the interior or core.  Lighter rocky components floated outward…..toward the Earth’s surface.

 Next, gaseous material escaped from Earth’s interior (through volcanoes) to produce the primitive atmosphere.  The primitive atmosphere was made of methane, ammonia and carbon dioxide. There was NO free oxygen (O 2 ) because it is too reactive.

 The Earth is composed of many different spheres. The different spheres describe different parts of our Earth.

The Earth’s Spheres!!!!

 The hydrosphere contains: All the water on the planet including the liquid water (oceans, lakes, rivers), the groundwater, the glaciers and ice caps, and the water found in the atmosphere.

 The glaciers and the ice-caps are also called the cryosphere.

 The oceans are the largest part of the hydrosphere!  They make up 71% of the Earth’s surface.  97% of the hydrosphere is found in the oceans.  The oceans are marine or salt water.

 The atmosphere is the thin gaseous layer that surrounds our planet.  It is comprised of 78% Nitrogen (N 2 ), 21% oxygen (O 2 ), 0-4% H 2 O v, 1% argon (Ar), and.038% carbon dioxide (CO 2 )

 The gases are held close to the Earth’s surface by gravity!  The atmosphere is divided into layers: troposphere, stratosphere, mesosphere, thermosphere and then the exosphere.

 The geosphere is part of the Earth’s major spheres.  The geosphere is made of the Earth’s interior, rocks/minerals, and landforms such as mountains.

 The geosphere is made of four parts: Crust (two types: oceanic and continental) Mantle Outer Core Inner Core

 The biosphere is the area on Earth where life can possibly be found. It covers the upper geosphere, the hydrosphere, and the lower atmosphere.

 Let’s explore the Solid Earth’s layers in more detail!

 The inner core is the innermost layer of the Earth.  The inner core is made of iron (80%) and nickel.  It is extremely hot… about ⁰ C.

 Even though the inner core is SO hot, it is a solid. Why is it a solid?

 The inner core extends from 6,360 km (the center of the earth) to 5,150 km (the bottom boundary of the outer core).

 The inner core is the densest part of the Earth. The density is 15 g/cm 3

 The existence of an inner core that is distinct from the liquid outer core was discovered in 1936 by seismologist Inge Lehmann using observations of earthquake-generated seismic waves that partly reflect from its boundary and can be detected by sensitive seismographs on the Earth's surface. outer coreInge Lehmannseismic wavesseismographs

 Outer Core!

 The outer core is the next layer of the Earth.  The outer core mainly consists of iron and nickel and about 10% sulphur and oxygen.

 The temperature in the outer core is about 4 500ºC.  Because of this high temperature, the outer core is molten or liquid.

 The density of the outer core is 11g/cm³.

 The outer core extends from 5,150 km (the boundary with the inner core) to 2, 890 km (the boundary with the mantle) below the earth's surface.

 The liquid outer core spins (because of convection & the Earth’s rotation).  The inner core does not spin because it is a solid.  So the outer core spins around the inner core.

 This spinning causes the earth's magnetic field.  Magnetism has been used by sailors to navigate the seas for thousands of years.  Magnetism also influences electro- particles outside the atmosphere of the earth (>37,000 miles into space).

The Mantle!

 The mantle is the largest part of the earth’s structure. It makes up 80% of the mass and 70% of the volume of the Earth!

 The mantle extends from 2, 890 km to ~65 km.  The density of the mantle ranges from 5 g/cm 3 (lower mantle) to 4 g/cm 3 (upper mantle)

ElementAmount CompoundAmount O44.8 Si21.5SiO 2 46 Mg22.8MgO37.8 Fe5.8FeO7.5 Al2.2Al 2 O Ca2.3CaO3.2 Na0.3Na 2 O0.4 K0.03K2OK2O0.04 Sum99.7Sum99.1

 The temperature of the mantle ranges from 3000 ⁰ C near the outer core to about 750 ⁰ C near the crust boundary. Pressure keeps the lower mantle solid.

 The mantle is mostly solid (because of high pressure) but contains a liquid portion called the asthenosphere.  The liquid portion (asthenosphere) is found in the upper mantle. This material moves by convection and is what causes plate tectonic movement and earthquakes!

 The region above the asthenosphere (upper mantle) and the entire crust are collectively called the lithosphere. This “layer” is solid and floats on the asthenosphere.

The Crust!

 There are two types of crust: oceanic and continental.  Continental crust is what makes up the continents, is thicker and less dense (2.7 g/cm 3 ).  Oceanic crust is what makes up the ocean depressions, is thinner, and more dense (3.0 g/cm 3 ).

 The crust is very thin: only 1% of the volume of the entire earth! It extends from the surface to around 65km deep.

 The crust is made of igneous, sedimentary and metamorphic rock.  Most of these rocks are made of silicates. OxidePercent SiO Al 2 O CaO6.4 MgO4.7 Na 2 O3.1 Fe as FeO6.7 K2OK2O1.8 TiO P2O5P2O5 0.1

 The crust is not one solid piece of rock. It is broken up into pieces called plates. The plates are made of the crust plus the upper mantle (lithosphere). These plates “float” on the asthenosphere and move.

 The temperature of the crust increases with depth, reaching values typically in the range from about 10°C (50°F) to 300°C at the boundary with the underlying mantle.

 The deepest hole ever dug is the Kola Superdeep Borehole, dug by the former USSR. The hole, SG-3, reached 12,261 metres (40,230 ft) in 1989, and remains the deepest hole ever drilled.