Earth Sciences 1086F/G Chapter Notes - Chapter 6-11: Convergent Boundary, Geology Of The Moon, Lava

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Unit 3 Notes – Earth Sciences
division of planets into terrestrial and gas/ice giants is based on density
The four terrestrial planets of our solar system are all close to the Sun, and rock bodies as the heat from the sun
is to greater for any of the planets to be made of mainly ice
Composition of ‘rocky’ material is common to all terrestrial planets: silicon (Si), oxygen (O), aluminum (Al),
magnesium (Mg), sulfur (S), and iron (Fe).
Basalt is common to all terrestrial planets
oBasalt: an igneous rock, the primary product of volcanic lava, fine grained, dark grey to black
The closer a planet is to the Sun, the more often will it be bombarded by incoming asteroids and comets
Chapter 6 – When Two Planets Collide
1.0 Introduction
The moon is unusual because…
oVery large relative to the planet it orbits
oAbnormally low density for an object associated with a terrestrial planet
oCore is 2-4% of total mass (compared to 30% for Earth’s core)
oAbnormally high angular momentum
Three suggestions of why the moon is a satellite of Earth (before 1970s), there was little hard evidence to
support any of the hypotheses
1. Fission Hypotheses – moon broke off from a rapidly spinning Earth
2. Condensation Hypothesis – Earth and Moon formed contemporaneously from the same material
3. Capture Hypothesis – Moon was formed as an independent planetary body that was later ‘captured; by
Earth during a close pass
The Fission Hypothesis
Proposed by George Darwin
Cannot be true because earth would have to rotate every 2.5 hours rather than every 24 hrs
Hypothesis was rejected
The Condensation Hypothesis
Hypothesis states: both bodies formed at the same time from exactly the same parental ‘cloud’ of dust and gas
The Earth and Moon do not have the same composition
The moon would also have to orbit Earth exactly on a equatorial plane, if not hypothesis is dead
The Capture Hypothesis
Problem: the gravitational and dynamic conditions need for an object the size of the Moon to fall into orbit
around Earth is unlikely
Problem: there are too many chemical similarities for the planets to be created in different places
Hypothesis is dead
The Giant Impact Hypothesis
Kinetic Energy – the energy of a body system with respect to the motion of the body, increases with velocity
A planet (Theia) somewhat smaller than Earth get Earth a small blow 4.5 billion years ago
The glancing blows gave an increased angular momentum to Earth
The metal core of the impactor separated and dropped into Earth (giving Earth a large metal core and high
Molten mantle material of both bodies mixed and formed debris in space just above Earth
Some debris fell back to Earth, but most collected to form the moon
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Recent Hypothesis:
1. Theia was nearly as massive as Earth, low velocity impact
2. High velocity impact with much smaller body, Earth spins very
fast (one day would last 2 hours)
3. Earth may have had two moons
Chapter 7 – Earth
Basic Earth Facts
third planet from the sun (1 astronomical unit from the sun)
fifth largest planet
densest major body in the solar system
one permanent naturel satellite
first planet out from the sun to have any natural satellite
plane of orbit is 7 degrees from the sun’s equatorial plane
orbital path is very nearly circular
the tilt of rotational axis (or obliquity or tilt angle) is primarily responsible for seasons
when Earth rotates, its rotational axis moves making a cone-like pattern – a process called “precession”
Earth’s magnetic field is uniquely strong
Earth’s atmosphere: 78% nitrogen, 21% oxygen, 1% miscellaneous
Earth’s Earliest History
Accretion – growth by accumulation of smaller bodies, dust and gas
Iron catastrophe
oHot liquid iron from the upper layer would begin to pool and sink under its own great weight
oThe amazing upheaval of the planet produced by iron sinking to the planet’s core released more energy
and caused the whole planet to melt
oThis caused great chaos as this process happened very quickly
The result of the iron catastrophe
o remove much – but certainly not all – of the iron from Earth’s outer layers to form a liquid core of
nearly 100% metal
oAs Earth grew, the pressure on the innermost core became so great that it transformed from a liquid to
a solid (giving Earth a hot central core of solid metal inside an outer core of liquid metal)
A Differentiated Earth
if we take a large portion of the single-most abundant element (iron)
and place it in Earth’s core, the outer volume must contain a higher
proportion of elements lighter than iron
differentiation – the process of chemical zonation from the core to the
oheaviest elements are at the core, lightest at the top
there are two different schemes to label the interior divisions of work
1. (the older way of defining) crust, mantle, and core
2. (the new way of defining that describes plate tectonics)
lithosphere, asthenosphere, mesosphere, outer core and inner core
Subdivisions on the left are based upon physical properties
Layers on the right are based on chemistry
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From surface to core pressure, temperature and density increases i.e. Rocks are generally lower density than the
material than the material they rest upon
Lithosphere – a solid relatively strong, rocky layer that includes the Earth’s crust and upper portion of the mantle
Asthenosphere – a layer of heat-softened, relatively weak, slow-flowing rock located 100-350km below the
earth’s surface
Mesosphere – wide zone below the asthenosphere with pressure so great that the rock has to be solid, has high
Core – separated into the inner core (solid) and outer core (liquid) – both are nearly pure metal, temperature of
core is hotter than the sun’s surface
Magnets and Magnetism
Erath is a dipole (2-pole) magnet
The most practical mechanism to generate a magnetic field is a dynamo
oThis device converts physical energy to electrical energy
The solid inner core of the Earth spins slightly faster than the rest of the Earth
Earth’s magnetic poles are how they are now normal
At times they switch: north becomes south magnetic pole reverse
Currently: the magnetic north pole has been slowly moving over the Artic region and has moved from Canadian
territory to international, and now headed to Russia
The Earth’s dynamo is ever-changing!
Plate Tectonics
Lithosphere is divided into a number of segments called plates
The plates moves as a result of the processes called tectonics that occur underneath them
London On is located on the North American plate
The Hypothesis of Continental Drift
Leonardo da Vinci – picked up a fossil of a sea shell on the top of a mountain, and realised that this fossil must
have come from the bottom of the ocean, therefore the sea floor must have been uplifted
Charles Darwin – favoured uplifting by da Vinci as he discovered the coastline of Chile had been raised up as a
result of an earthquake
Alfred Wegener – he said that at one time there was no pacific ocean, and all the contents were one big
continent called Pangaea
Process of Pangea braking up is called continental drift
The Rock Magnetic Pattern
Paleomagnetism – the study of magnetic properties of rocks
Curie point – a temperature where atoms are very active but below that temperature, much less so
Plate Margins
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