Week 1: Earth 2 Lecture Notes
LIFE: SCIENCE STORIES
LIFE'S GREATEST SERIES OF SCIENCE STORIES
Topic encompasses various aspects of Earth's formation and structure.
Presented in both pictures and text.
READING ASSIGNMENTS
Various sections assigned corresponding to each lecture and lab sessions.
Focus topics covered include:
Early Earth: Formation and structure.
Plate tectonics fundamentals.
Types of rocks: Igneous, sedimentary, and metamorphic.
Geological time scale and Earth's history.
EARTH'S STRUCTURE
1. Chemical Composition
Crust (Silicate)
Major elements: O (46%), Si (28%), Fe (6%), Al (8%), Ca (3%), Mg (3%), Na (2%), K (2%).
Mantle (Silicate)
Major elements: O (44%), Si (21%), Fe (6%), Al (2%), Ca (2%), Mg (23%), Na (0.3%), K (<0.1%).
Core (Fe-Ni Alloys)
Major elements: Fe (86%), Si (6%), Ni (5%), S (2%), Cr (1%).
2. Structure by Strength
Lithosphere:
Strong; includes crust and the uppermost, cooler part of the mantle.
Forms tectonic plates; does not undergo convection.
Asthenosphere:
Deformable solid layer of the mantle that flows plastically.
Starts at depths of >1280
3. Continental Vs. Oceanic Crust
Continental Crust:
Thickness: 30–90 km; lithosphere thickness: 200–250 km.
Composition: Higher Si, lower Mg.
Age: Older on average (up to 4 Ga).
Complexity: More complex structure.
Oceanic Crust:
Thickness: 0–7 km; lithosphere thickness: 50–100 km.
Composition: Lower Si, higher Mg.
Age: Younger (≤200 Ma).
Complexity: Less complex structure.
4. Techniques to Probe Earth's Interior
A. Continental Drilling
Kola Superdeep Borehole (1970-1989 in Northern Russia): Reached 12,262 m (7.6 miles).
International Ocean Drilling Program: Deepest oceanic drill hole at 1,806 m (1.12 miles).
B. Seismic Wave Analysis
Large earthquakes create seismic waves that can be felt globally.
Two major wave types:
P-waves (Primary):
Compressional waves; can travel through solids and liquids.
S-waves (Secondary):
Shear waves; can only travel through solids.
S-wave Shadow Zone: Area where S-waves do not reach, indicating a liquid outer core.
C. Xenoliths
Pieces of lower crust and upper mantle brought up in volcanic eruptions.
Provide direct samples for studying deep Earth composition.
Volcanic processes involve magma interaction with hydrothermal systems, gas exsolution, and magma mixing, which facilitate the transport of these rock fragments to the surface during eruptions.
D. Tectonic Exposures (During collision, oceanic crust gets shoved up on continent)
Exposures of lower crust and upper mantle due to plate tectonic activity (obduction).
Allows for direct observation and study of cross-sections of oceanic crust.
Example: Ophiolite sequences in Oman and the UAE show geological units like peridotite, sheeted dikes, and lavas, representing exposed oceanic lithosphere.
SEISMIC WAVE BEHAVIOR
1. Refraction and Reflection
Seismic waves refract (bend) at transitions between different materials (layer boundaries).
Waves can also reflect off layer boundaries.
2. Example of Seismic Behavior
P-wave Shadow Zone:
Notable angle zones where P-waves do not propagate due to changes in material properties.
PLATE TECTONICS
1. Definition and Driving Force
Theory that describes the large-scale motion of Earth's lithosphere.
Driven by convection currents within Earth's mantle.
2. Types of Plate Boundaries
Divergent Boundaries:
Plates move apart from each other.
Creates new crustal material (e.g., mid-ocean ridges, rift valleys).
Convergent Boundaries:
Plates move towards each other.
Can result in subduction (oceanic plate sinking) or continental collision (e.g., trenches, volcanic arcs, mountain ranges like the Himalayas).
Transform Boundaries:
Plates slide horizontally past each other.
Crust is neither created nor destroyed (e.g., San Andreas Fault).
3. Associated Phenomena
Earthquakes, volcanism, and mountain building are common geological processes associated with plate boundaries.
EARTH'S HYDROSPHERE
Water Budget
Oceans: 97.5% (and rising).
Glaciers: Approximately 2% (and decreasing).
Groundwater: ~1%.
Lakes, Rivers & Streams: ~0.1%.
Clouds: <0.001%.
EARTH'S ATMOSPHERE
Characteristics
Atmospheric pressure at Earth's surface is 1 bar (equivalent to 14.5 pounds per square inch).
EARTH'S MAGNETIC FIELD
Generated by convection of liquid iron in the outer core.
Solar wind (electrons, protons, and helium nuclei) interacts with atmospheric particles, producing auroras in the polar regions.
INTRODUCTION TO ATOM
Atom Structure
Protons: Positive charge.
Electrons: Negative charge.
Neutrons: No charge.
Nucleus: Composed of protons and neutrons. Electrons orbit around the nucleus.
Isotopes
Variants of elements with the same number of protons but differing neutron counts (e.g., $^{204}\text{Pb}$, $^{206}\text{Pb}$, $^{207}\text{Pb}$; all having 82 protons).
States of Matter
Solid: Fixed volume and shape due to tightly bound atoms/molecules.
Liquid: Fixed volume but takes the shape of the container due to loosely bound atoms/molecules.
Gas: Expands to fill any volume due to atoms/molecules in random motion.
GEOLOGIC SOLIDS
Rock and Minerals
Rock: Naturally occurring solid, composed of aggregates of minerals or a mass of glass.
Minerals: Solids with specific crystalline structures and chemical compositions.
Example: Tonalite comprises minerals such as quartz, plagioclase, and amphibole.
TYPES OF ROCKS
1. Igneous Rocks
Formed from the cooling and solidification of molten rock (magma or lava).
Intrusive (Plutonic):
Cools slowly beneath Earth's surface, forming large crystals (e.g., granite).
Extrusive (Volcanic):
Cools rapidly at or near Earth's surface, forming fine-grained or glassy textures (e.g., basalt, obsidian).
2. Sedimentary Rocks
Formed from the accumulation and compaction of sediments, or by chemical precipitation.
Clastic Sedimentary Rocks:
Composed of weathered fragments of other rocks (e.g., sandstone, shale).
Chemical Sedimentary Rocks:
Formed from the precipitation of minerals from water (e.g., limestone, rock salt).
Organic Sedimentary Rocks:
Formed from the accumulation of organic matter (e.g., coal).
3. Metamorphic Rocks
Formed when existing rocks are subjected to intense heat, pressure, or chemical alteration.
Foliated Metamorphic Rocks:
Exhibit layers or bands due to directed pressure (e.g., slate, schist, gneiss).
Non-foliated Metamorphic Rocks:
Do not have a layered or banded appearance (e.g., marble, quartzite).
FORMATION OF THE EARTH
1. The Big Bang
The universe began approximately 13.8 billion years ago, resulting in the formation of hydrogen and helium.
2. Nucleosynthesis
Process whereby elements heavier than helium are formed during the lifecycle of stars through fusion reactions.
Leads to the generation of new heavier elements at extreme temperatures and pressures.
3. Solar Nebula
Formation of the solar system occurred from a cloud of gas and dust (solar nebula/start of planetary formation) approximately 4.567 billion years ago.
Gravitational collapse led to the formation of a proto-star.
4. Planet Formation
Rocky planets formed in the inner solar system, while gaseous planets formed beyond the frost line between Mars and Jupiter.
5. Early Earth Evolution
Formation of Earth’s core due to impacts, compaction, and radioactive decay.
6. Moon Formation Theory
Moon is thought to have formed from a collision of Earth and a Mars-sized body early in Earth's history.
AGE OF THE EARTH
1. Historical Estimates
Early beliefs circled around a few thousand years of Earth's age.
James Hutton (1788): advocated that Earth has no beginning or end.
Lord Kelvin (1864–1897): estimated a range of 20–40 million years.
2. Current Understanding
The age of the Earth is estimated to be 4.567 billion years based on radioactive decay measurements.
RADIOACTIVE DECAY
1. Fundamentals
Unstable isotopes decay to more stable daughter isotopes over time.
Half-life (): the time it takes for half of the parent isotopes to decay.
Example: Uranium-238 () decays to Lead-206 () with a half-life of 4.468 billion years.
2. Isotope Ratio Analysis
Age of materials can be determined by measuring the ratios of parent to daughter isotopes.
TIMELINE FOR EARLY EARTH
4.567 ± 0.0006 Ga: Formation of Solar Nebula/planets.
4.51 ± 0.01 Ga: Crystallization of lunar crust.
4.40 ± 0.008 Ga: Oldest zircon from Jack Hills, Australia (indicating early solid crust).
4.03–4.00 Ga: Oldest igneous rocks, such as Acasta Gneiss.
EARLIEST LIFE
Evidence of life suggests potential origins by 3.7 Ga, indicating conditions with liquid water.
CONCLUSION
The formation and evolution of Earth are defined by a timeline solidified through advancements in isotopic dating and geological studies, tracing back to the conditions necessary for life itself.