Geology in the News: Largely as a result of hydraulic fracturing technology, the U.S.A. is now the world's leading producer of natural gas. Largely as a result of hydraulic fracturing technology, the U.S.A. is now the world's leading producer of natural gas. Shell Oil has just reported major new production from the Utica Shale of upstate New York and adjacent Pennsylvania. Shell Oil has just reported major new production from the Utica Shale of upstate New York and adjacent Pennsylvania.

ORIGINS (cont.)

To recap from Friday: Nuclear Fusion is what generates the energy of stars Nuclear Fusion is what generates the energy of stars Minimum temperature for: 10 million - Hydrogen to fuse into helium: 10 million° Kelvin 100 million - 3 helium nuclei to fuse into carbon: 100 million° Kelvin 90% of all matter in the Universe consists of Hydrogen and Helium 90% of all matter in the Universe consists of Hydrogen and Helium Matter in the known Universe was originally quite uniformly distributed. Matter in the known Universe was originally quite uniformly distributed.

Due to gravitational attraction [, this matter slowly condensed into clouds, now called nebulae (or nebulas)... Due to gravitational attraction [ F grav ~ ( m 1 m 2 )/ d 2 ], this matter slowly condensed into clouds, now called nebulae (or nebulas)...

Individual stars are created as large areas of gas within the nebula condense, if these gas pockets have sufficient mass (i.e., ~10x that of Jupiter).

The nebulae continually collapse and commonly start rotating, to form galaxies, like the Andromeda Galaxy, pictured here. (Note the other galaxies also in the picture!) WE ARE HERE! ( Our own Milky Way Galaxy is a spiral galaxy ) Typical galaxies contain hundreds of millions to billions of stars.

There are a LOT of galaxies out there! THIS is what the Hubble space telescope saw when aimed at an "empty" part of the sky – an area about the size of the head of a pin held at arm's length!

our BUT our original star didn't last …. It exploded in what is called a SUPERNOVA SUPERNOVA.

What is the evidence for this Supernova?

The process of nuclear fusion can only generate elements as heavy as iron - with 26 protons and either 29 or 30 neutrons in the nucleus - within an active star's core.

Iron But if we look at the period table, we see LOTS of elements that are heavier than iron!

Supernova The Supernova is required to generate the pressures and temperatures to create these heavier elements!

This supernova – the exploding star - created a vast cloud of debris, still with abundant hydrogen and helium, but also including many heavier elements derived from the star's demise.

Debris coalescing within this gas cloud produced larger fragments of solids, that coalesced into small bodies called planetesimals…. …. that then further coalesced to form larger solid bodies - planets - rotating around a central star …. the Sun.

Soooooo, ultimately we wind up with the solar system we call HOME. (Ever wonder why all the planets except for Pluto rotate in the same direction around the sun, in a flat plane?) All this is believed to have happened some time around five BILLION years ago. (Remember that the Big Bang was b.y.a., some 8-9 billion years earlier!)

THE EARLY EARTH Probably pretty active - initially molten, then skinned over with Probably pretty active - initially molten, then skinned over with a thin surface layer, continually broken by volcanic activity. a thin surface layer, continually broken by volcanic activity.

But by 3.8 billion years ago, we know we had primitive oceans. The "primordial soup" of the early oceans held a variety of strange and very primitive organisms, such as mats of algae that formed stromatolites like these in Australia >

< billion-year-old stromatolites in South Africa 2.6-billion-year-old microfossils (of bacteria) from North America, on the north shore of Lake Superior >

Rocks of this ancient crust also show clearly that they've been through a lot. This is a satellite image of ancient rocks in Australia - the image is ~ 200 km across! The light areas are granitic rocks, ancient mini- continental blocks, while the green belts are ancient volcanic rocks that were crushed in between.

By this time, the Earth was also stratified into layers, with most of the heavier elements (particularly iron) being concentrated in the central core. (We had also lost most of our hydrogen and helium to space by this time….)

5-70 km thick5-70 km thick km under continents, km under ocean basins continental & oceanic crust are intrinsically differentcontinental & oceanic crust are intrinsically different Continental crust esp. enriched in lighter elements (O, Si, Al, Na, K)Continental crust esp. enriched in lighter elements (O, Si, Al, Na, K) - relatively low in Fe, Mg, Ni - relatively low in Fe, Mg, Ni - density grams/cm 3 - density grams/cm 3 - highly complex & heterogeneous km thick Oceanic crust more like mantle beneath itOceanic crust more like mantle beneath it - lower in Si, Al, Na, K - higher in Ca, Fe, Mg - density grams/cm km thick The CRUST is that which we know best.

km (1800 mi) thick - comparable to the distance from Maine to Colorado km (1800 mi) thick - comparable to the distance from Maine to Colorado - depleted of light elements (Al, K, Na) - depleted of light elements (Al, K, Na) - believed to be mainly Fe, Mg silicates (top) and Fe, Mg oxides (at base) - believed to be mainly Fe, Mg silicates (top) and Fe, Mg oxides (at base) - density 3.5 grams/cm 3 (top) to 5.5 grams/cm 3 (bottom) - density 3.5 grams/cm 3 (top) to 5.5 grams/cm 3 (bottom) - source for most magmas (molten rock) - source for most magmas (molten rock) The MANTLE is beneath the crust

The CORE is composed mostly of iron (Fe) with some nickel (Ni) Inner Core km thick (1300 mi) - molten - flow generates magnetic field (how?) - density grams/cm km radius (750 mi) - probably solid - density grams/cm 3 (2x density of iron at surface; = Pb) (2x density of iron at surface; = Pb) Outer Core

NO ONE HAS ACTUALLY SEEN THE MANTLE OR THE CORE What we believe about them is based on: 1. Meteorites

2. inclusions in volcanic rocks called xenoliths

3. rare rocks (fragments of uppermost mantle) exposed in mountains where upper parts of the oceanic crust and mantle are folded, buckled & pushed up ( called ophiolites). Peridotite

4. behavior of seismic waves from earthquakes & large explosions (e.g., nuclear tests) 5. theoretical studies

BUT for MOST of the semester, we're going to be focusing on the part we know the best - the crust. (Be it ever so humble, there's no place like home!)

Wednesday: Plate tectonics ~ A revolution hits the Earth Sciences