Unit 2-Solid EarthUnit 2-Solid EarthIntroduction to Planet Introduction to Planet

“Earth” “Earth”

Formation of the Universe-Big Formation of the Universe-Big Bang TheoryBang Theory

Big BangBig Bang

Formation of Solar System and Formation of Solar System and EarthEarth

Nebular hypothesisNebular hypothesis Nebula=cloud of gases and space Nebula=cloud of gases and space

dustdustMainly hydrogen and heliumMainly hydrogen and helium

Gravity concentrates material at Gravity concentrates material at center of cloud (Sun)center of cloud (Sun)

Protoplanets from smaller Protoplanets from smaller concentrations of matter (eddies)concentrations of matter (eddies)

ProtoearthProtoearth Larger than Earth todayLarger than Earth today Homogeneous compositionHomogeneous composition Bombarded by meteoritesBombarded by meteorites

Moon formed from collision Moon formed from collision with large asteroidwith large asteroid

Heat from solar radiationHeat from solar radiation Initial atmosphere boiled awayInitial atmosphere boiled away Ionized particles (solar wind) Ionized particles (solar wind)

swept away nebular gasesswept away nebular gases

ProtoearthProtoearth

Radioactive heatRadioactive heat Spontaneous disintegration of Spontaneous disintegration of

atomsatoms Heat from contraction (protoplanet Heat from contraction (protoplanet

shrinks due to gravity)shrinks due to gravity) Protoearth partially meltsProtoearth partially melts Density stratification (layered Density stratification (layered

Earth)Earth)

Earth’s internal structureEarth’s internal structure Highest density material at Highest density material at

center (core)center (core) Lowest density material at Lowest density material at

surface (crust)surface (crust) Earth layeredEarth layered

Chemical compositionChemical composition Physical propertiesPhysical properties

Chemical compositionChemical composition CrustCrust

Low-density, mainly silicate Low-density, mainly silicate mineralsminerals

MantleMantle Mainly Fe and Mg silicate Mainly Fe and Mg silicate

mineralsminerals CoreCore

High-density, mainly Fe and NiHigh-density, mainly Fe and Ni

Layered Layered EarthEarth

Fig. 1.14

Physical propertiesPhysical properties

LithosphereLithosphere AsthenosphereAsthenosphere MesosphereMesosphere Outer coreOuter core Inner coreInner core

Physical propertiesPhysical properties LithosphereLithosphere

Cool, rigid, brittleCool, rigid, brittle Surface to about 100 km (62 miles)Surface to about 100 km (62 miles)

AsthenosphereAsthenosphere Warm, plastic, able to flowWarm, plastic, able to flow From 100 km to 700 km (430 miles)From 100 km to 700 km (430 miles)

Fig. 1.15

LithosphereLithosphere

Oceanic crustOceanic crust Underlies ocean basinsUnderlies ocean basins Igneous rock basaltIgneous rock basalt Average thickness 8 km (5 miles)Average thickness 8 km (5 miles) Relatively high densityRelatively high density

3.0 g/cm3.0 g/cm33

Lithosphere- Lithosphere- Crust and Crust and Uppermost mantle fused Uppermost mantle fused togethertogether.. Continental crustContinental crust

Underlies continentsUnderlies continents Igneous rock graniteIgneous rock granite Average thickness 35 km (22 Average thickness 35 km (22

miles)miles) Lower densityLower density

2.7 g/cm2.7 g/cm33

AsthenosphereAsthenosphere

Upper mantleUpper mantle Plastic—deforms by flowingPlastic—deforms by flowing High viscosity—flows slowlyHigh viscosity—flows slowly

Isostatic adjustmentIsostatic adjustment BuoyancyBuoyancy

Less dense “floats” higher than more denseLess dense “floats” higher than more dense

Continental crust “floats” higher than oceanic crust on plastic Continental crust “floats” higher than oceanic crust on plastic asthenosphereasthenosphere

Questions: Questions: Based on Isostatic adjustment, what is the impact of removing a large percentage of groundwater from California?Based on Isostatic adjustment, what is the impact of removing a large percentage of groundwater from California? Based on geologic response, what is the impact of removing a large percentage of groundwater from California?Based on geologic response, what is the impact of removing a large percentage of groundwater from California?

Fig. 1.16

Origin of Earth’s Origin of Earth’s atmosphereatmosphere Partial melting resulted in Partial melting resulted in

outgassingoutgassing about 4 billion years about 4 billion years agoago Similar to gases emitted from Similar to gases emitted from

volcanoesvolcanoes Mainly water vaporMainly water vapor Carbon dioxide, hydrogenCarbon dioxide, hydrogen Other gases such as methane and Other gases such as methane and

ammoniaammonia

Evolution of Earth’s AtmosphereEvolution of Earth’s Atmosphere

Some scientists describe three stages in the evolution of Earth’s atmosphere as it is today

Just formed Earth: Like Earth, the hydrogen (H2) and

helium (He) were very warm. These molecules of gas moved so fast they escaped Earth's gravity and eventually all drifted off into space.1.Earth’s original atmosphere was probably just hydrogen and helium, because these were the main gases in the dusty, gassy disk around the Sun from which the planets formed. The Earth and its atmosphere were very hot. Molecules of hydrogen and helium move really fast, especially when warm. Actually, they moved so fast they eventually all escaped Earth's gravity and drifted off into space.

Young Earth: Volcanoes released gases H2O (water) as steam, carbon dioxide (CO2), and ammonia (NH3). Carbon dioxide dissolved in seawater. Simple bacteria thrived on sunlight and CO2. By-product is oxygen (O2).Earth’s “second atmosphere” came from Earth itself. There were lots of volcanoes, many more than today, because Earth’s crust was still forming. The volcanoes released steam (H2O, with two hydrogen atoms and one oxygen atom), carbon dioxide (CO2, with one carbon atoms and two oxygen atoms),

ammonia (NH3, with one nitrogen atom and three hydrogen atoms).

Current Earth: Plants and animals thrive in balance. Plants take in carbon dioxide (CO2) and give off oxygen (O2). Animals take in oxygen (O2) and give off CO2. Burning stuff also gives off CO2.Much of the CO2 dissolved into the oceans. Eventually, a simple form of bacteria developed that could live on energy from the Sun and carbon dioxide in the water, producing oxygen as a waste product. Thus, oxygen began to build up in the atmosphere, while the carbon dioxide levels continued to drop. Meanwhile, the ammonia molecules in the atmosphere were broken apart by sunlight, leaving nitrogen and hydrogen. The hydrogen, being the lightest element, rose to the top of the atmosphere and much of it eventually drifted off into space.

Now we have Earth’s “third atmosphere,” the one we all know and love—an atmosphere containing enough oxygen for animals, including ourselves, to evolve.

So plants and some bacteria use carbon dioxide and give off oxygen, and animals use oxygen and give off carbon-dioxide—how convenient! The atmosphere upon which life depends was created by life itself. 

Origin of Earth’s oceansOrigin of Earth’s oceans

Water vapor released by Water vapor released by outgassingoutgassing

Condensed as rainCondensed as rain Accumulated in ocean basinsAccumulated in ocean basins About 4 billion years agoAbout 4 billion years ago Ice Comets were also important Ice Comets were also important

to adding water to the Earth to adding water to the Earth systemsystem

Fig. 1.17

Volcanic outgassing of Kilauea volcano on Hawai’i

Ocean salinityOcean salinity Rain dissolves rocksRain dissolves rocks Dissolved compounds (ions) Dissolved compounds (ions)

accumulate in ocean basinsaccumulate in ocean basins Ocean salinity based on Ocean salinity based on

balance between input and balance between input and output of ionsoutput of ions

Ocean salinity nearly constant Ocean salinity nearly constant over past 4 billion yearsover past 4 billion years

Life in oceansLife in oceans

Earliest life forms fossilized Earliest life forms fossilized bacteria in rocks about 3.5 bacteria in rocks about 3.5 billion years oldbillion years old

Marine rocksMarine rocks Life originated in oceans?Life originated in oceans?

Stanley Miller’s experimentStanley Miller’s experiment

Organic molecules formed by Organic molecules formed by ultraviolet light, electrical spark ultraviolet light, electrical spark (lightning), and mixture of water, (lightning), and mixture of water, carbon dioxide, hydrogen, methane, carbon dioxide, hydrogen, methane, and ammoniaand ammonia

Fig. 1.18a

Evolution and natural Evolution and natural selectionselection Organisms adapt and change Organisms adapt and change

through timethrough time Advantageous traits are naturally Advantageous traits are naturally

selectedselected Traits inheritedTraits inherited Organisms adapt to environmentsOrganisms adapt to environments Organisms change environmentsOrganisms change environments

Types of life formsTypes of life forms HeterotrophsHeterotrophs (most bacteria (most bacteria

and animals)and animals) AutotrophsAutotrophs (algae and (algae and

plants)plants) Anaerobic bacteria Anaerobic bacteria

(chemosynthesis)(chemosynthesis) Photosynthetic autotrophsPhotosynthetic autotrophs

Chlorophyll captures solar Chlorophyll captures solar energyenergy

Photosynthesis and Photosynthesis and respirationrespiration

Fig. 1.19

Oxygen crisisOxygen crisis Photosynthetic bacteria release Photosynthetic bacteria release

oxygen (Ooxygen (O22) to atmosphere) to atmosphere About 2 billion years ago, About 2 billion years ago,

sufficient Osufficient O22 in atmosphere to in atmosphere to oxidize (rust) rocksoxidize (rust) rocks

Ozone (OOzone (O33) builds up in ) builds up in atmosphereatmosphere Protects Earth’s surface from Protects Earth’s surface from

ultraviolet solar radiationultraviolet solar radiation

Oxygen crisisOxygen crisis

About 1.8 billion years ago, most About 1.8 billion years ago, most anaerobic bacteria killed off by anaerobic bacteria killed off by OO22-rich atmosphere-rich atmosphere

Photosynthetic organisms Photosynthetic organisms created today’s Ocreated today’s O22-rich -rich atmosphere atmosphere OO22 makes up about 21% of gases in makes up about 21% of gases in

modern atmospheremodern atmosphere Animals thriveAnimals thrive

Age of EarthAge of Earth Radiometric age datingRadiometric age dating

Spontaneous change/decaySpontaneous change/decay Half-lifeHalf-life

Earth is about 4.6 billion years oldEarth is about 4.6 billion years old

Fig. 1.22

Geologic Geologic time scaletime scale

Fig. 1.H

End of End of CHAPTER 1 CHAPTER 1 Introduction Introduction to Planet to Planet “Earth”“Earth”