So Hot! Why? Early Earth 4.6bya

Proximity to new sun Accretion: Collisions > greater mass, gravity, pressure

The Sun Forms • Clears the solar system collisions Therefore fewer collisions • Earth’s surface begins to cool • water vapor escapes, condenses into clouds, rain, furthering the cooling In the very beginning of earth's history, this planet was a giant, red hot, roiling, boiling sea of molten rock - a magma ocean. The heat had been generated by the repeated high speed collisions of much smaller bodies of space rocks that continually clumped together as they collided to form this planet. As the collisions tapered off the earth began to cool, forming a thin crust on its surface. As the cooling continued, water vapor began to escape and condense in the earth's early atmosphere. Clouds formed and storms raged, raining more and more water down on the primitive earth, cooling the surface further until it was flooded with water, forming the seas. A cooling Earth

• Residual heat from formation • Radioactive decay of unstable atoms Inner planet remains hot • Residual heat from formation • Radioactive decay of unstable atoms In decay, atoms eject nuclear particles and release high energy (gamma) radiation

Layers form Cooling Earth differentiates into layers:

Core Inner – greatest density, pressure, temperature Solid due to pressure, despite heat Outer – less pressure, therefore molten Evidenced by volcanism

Evidence for an iron core from meteorites Abundance of elements in meteorites reflects the abundance of elements everywhere in the early solar system, Earth included Once the volatiles are burned off, an iron core remains GEOCHEMISTS have frequently used the abundances of elements in meteorites as a guide to the overall composition of the Earth. The abundances in the chondritic meteorites have been commonly used on the assumption that they represent the closest approach to the composition, for the non-volatile elements, of the primitive unfractionated material in the solar system. iron meteorite Russia, 2013

Evidence for a dense core from direct observation of rocks Crust/mantle rocks less dense than the earth as a whole (crust: 2.8g/cc vs 5.5g/cc) the interior must be made of a material whose density is considerably greater than Earth’s average density to compensate enoliths are formed when magma rising from deep levels rips off pieces of the rock which it passes through (the country rock ) and carries these pieces along with it. Mantle rocks torn off, carried along with rising mantle material

Evidence for dense metal core inferred from chemical composition More massive, dense, atoms sink to center of forming planet Mass a.m.u. Density g/cm3 Si 14 2.33 O 16 .001 Mg 12 1.74 Fe 26 7.87 Ni 28 8.9 Fe in the inner core; NiFe alloy in outer core

Evidence for molten metal outer core from the magnetic field Earths axial spin, creates electric currents in outer core Currents in turn create a magnetic field e- e- e- e- spin a factor too Solar wind? Stream of particle blown off the suns corona Polarity is the direction of the current, now N e- e- Cartoon explanation 100 greatest discoveries

Magnetic field has reversed over time, repeatedly, leaving a record in the rocks. cooled rocks, magnetic particles ‘frozen’ Sea floor has an extensive record of the reversals

This magnetosphere protects the earth from the solar wind Rocks that form from magma retain a record of the earth;s polarity as the magnetic particles align with the filed when molten.

Where the magnetosphere is thin, we see the interaction of the atmosphere with the solar wind Trapped particles of the solar wind spin around the magnetic field lines Auroras have been moving, may be evidence of a shift in the earths polarity Expected every 250,000 years; its been > 780,000! Auroras are the spectra generated when the particles are energized in collisions with atmosphere Aurora Borealis

Evidence for a solid/molten inner/outer core from earthquake wave behavior S-waves do not transmit through fluids, or the outer core

Mantle Mantle • Mid-density SiO2 2.65 MgO 3.58 Ni & Fe 9.9 Less Fe than core More MgO than crust Less SiO2 than crust Mantle Density g/cm3 SiO2 2.65 MgO 3.58 Ni & Fe 9.9

• Heated by the core at its base, cool at the crust, creating convection currents • A fluid solid - albeit flowing very slowly solid – state of matter fluid – describes behavior Olivine from the mantle Like Silly Putty!

Crust Density g/cm3 SiO2 2.65 MgO 3.58 NiFe 9.9 • Broken into plates as the planet cooled, shrank • Highest in SiO2, lowest in FeO, MgO

• Broken into plates as the planet cooled, shrank • Highest in SiO2, lowest in FeO, MgO • Two types: sea floor crust: thin, basalts continental crust: thick, granitic

Last word… …percent abundance crust mantle SiO2 60.6 46 MgO 4.7 37.3 FeO 6.7 7.5

Alternate Layering Scheme lithosphere Rigid crust plus upper mantle asthenosphere warmer mantle