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Chapter 1: Cosmology
Cosmology and the Birth of the Earth
1.1 Introduction
In the context of scientific cosmology, the Universe contains of 2 basic entities:
Matter: the material substance of the universe, it consists of atoms and has mass.
Energy: the capacity to do work.
1.2 An Image of Our Universe
Geocentric model = an ancient Greek idea suggesting that the Earth sat motionless in the center of the Universe while stars and
other planets and the Sun orbited around it.
Heliocentric model = the idea that all heavenly objected including the Earth orbited the Sun.
🌍 Planet = An object that orbits a star, is roughly spherical and
has cleared its neighbourhood of other objects. (three
properties)
Over time, stars appear to → exoplanet = planet that orbits around other stars
Over time, planets appear to
revolve around in circles.
wander (retrograde motion). Wanderer = planēs in Greek. Thats where the word planet comes from.
terrestrial planets = planets that are of
The Earth is located in the Solar System
Mercury, Venus, Earth and Mars comparable size and character to the Earth and and orbits around a star called the Sun.
(the inner planets) consist of a metallic core surrounded by a rock Our Sun is one of over 300 billion stars in
mantle the Milky Way Galaxy. There are billions
giant planets (jovian planets) → Jupiter and of galaxies in the universe.
Jupiter, Saturn, Uranus and
Saturn are called gas giants → Uranus and
Neptune (the outer planets)
Neptune are called ice giants
Chapter 1: Cosmology 1
, Other objects in the solar system:
Moons A sizeable solid body, locked in orbit around a planet.
A relatively small rocky or metallic object that orbits the Sun, most lie between the orbits of Mars and
Jupiter.
Asteroids
Known asteroids can range in diameter from 1 cm to 930 km
Icy bodies lying outside the orbit of Neptune, those that occur in a donut-like ring form the Kuiper Belt and
Kuiper Belt and Oort Cloud
more distant ones form the Oort Cloud Objects. They can range in diameter from less than 1 cm to 2000
Objects
km
An asteroid with a diameter greater than about 900 km that has not cleared its orbit of debris.
Dwarf Planets
The only five identified dwarf planets are: Pluto, Eris, Haumea, Ceres and Makemake
Comets Kuiper Belt or Oort Cloud Objects that follow an elliptical orbit that brings them into the inner Solar System.
How was the circumference of the earth calculated?
The Greek astronomer Eratosthenes (ca. 276-194 BC) was the first to
come up with a good estimate. He compared the angle of the light from
the Sun on Earth in two different places; Alexandria and Syene. By using
the distance between the places (≈5000 stadia), he estimated that the
circumference of the Earth was 250,000 stadia ≈ 39,300 km. This is
very close to today’s value of 40,008 km.
💡 Light-year = the distance that light travels in one (Earth)
year, which is about 9.5 trillion kilometers.
The nearest star to Earth is called Alpha Centauri and lies about
40.85 trillion km or 4.37 light-years away. This means that the light
we see from the star when we look at the sky, left the star 4.37
years ago.
The Earth has proven motion in three ways: around its axis, around the
Sun and around the centre of the Milky Way.
1.3 Forming the Universe
Doppler Effect = a phenomenon in which the frequency of wave energy appears to change when a moving source of
wave energy passes an observer
→ A source of sound or light (which is a form of electromagnetic radiation) emits waves. When that source is moving towards
an observer it seems like the wavelength becomes shorter and therefore the frequency (= amount of waves per time interval)
higher. This is because the source has moved closer to the observer since the last wave was emitted.
In the colour spectrum, red has a lower frequency and
blue has a higher frequency. Therefore light can be
observed with a red shift or a blue shift.
Chapter 1: Cosmology 2
, 🍞 Expanding Universe theory = the theory that the whole universe must be expanding because galaxies in every
direction seem to be moving away from us.
→ Astronomers noticed that all the light coming from distant galaxies
displayed a red shift relative to the light coming from nearby stars. So the
Universe can be seen as a ball of bread dough with raisins that expands
when it bakes, where each raisin moves away from its neighbours. By this
analogy, galaxies that lie farther away are moving away faster than the
nearby galaxies.
💥 Big Bang Theory = the theory where a cataclysmic explosion represents the formation of the Universe.
→ Before the Big Bang (about 13.8 billion years ago) all matter and all energy (everything that exists) was packed into an
infinitely small point called a singularity.
Inflationary epoch = in less than a second the
What happened right after the Big Bang?
Universe expanded incredibly fast, then it slowed
There was only energy and a lot of heat.
down
Big Bang nucleosynthesis = the first atoms with up to 5 protons form.
Molecules also started to form.
The Universe expanded and cooled further which caused the atoms and
molecules to slow down and accumulate into patchy clouds called
nebulae.
How are protostars made?? (± 200 million years later) How are stars made?? (± 400 million years later)
Molecules started to form specks of ice. The protostar continued to grow and became denser to a
temperature of about 10 million °C.
The gravity from the nebulae started sucking in surrounding ice and
gas, this caused it to have more gravity and suck in more ice and The hydrogen nuclei slam together forming helium through fusion
gas. (= if two nuclei fuse). This causes the mass to become hotter and
hotter.
As the matter continued to move inward, the rotation rate became
faster and faster. This made the nebula evolve into a disk shape. The ‘ignition’ of the first fusion formed a star (of the first
generation).
Gravity collapsed the inner portion of the disk into a dense ball.
This ball kept growing and it became so hot its started to glow, this is Astronomers have shown that the larger the star, the hotter it
the birth of a protostar. burns, and the faster it runs out of fuel and dies.
Supernova = the explosion (dying) of a giant star
1.4 We Are All Made of Stardust
Stellar nucleosynthesis = the production of new, larger atoms (with atomic numbers between 5 and 25) by fusion
reactions in stars.
→ When these new atoms are formed some manage to escape the stars gravity before it dies, this stream is called a stellar
wind.
🎏 Differentation = an early phase in a planet's history where dense iron alloy melts, forms the core, and leaves a less
dense mantle.
→ This heat that lets the iron melt comes from three sources:
1. Collisions 2.
Matter squeezes into a smaller volume
3. Decay of radioactive elements
1 billion years ago = 1 Ga (gigaannum)
Chapter 1: Cosmology 3
, Low mass stars emits atoms when it dies and becomes a red giant
blasts atoms into space when it dies during a supernova explosion,
High mass stars during this bigger atoms can also be formed = supernova
nucleosynthesis
🎇 Nebular Theory (condensation theory) = the idea that our Solar
System formed out of a nebula. The Solar System formed about 9
billion years after the Big Bang.
1. There is a nebula made out of matter.
2. The matter starts absorbing nearby matter, causing a chain reaction that
increases the core's gravitational pull and initiates spinning. A
protoplanetary disk forms as outer materials resists absorption due to their
speed. This disk is sectioned into two parts by a frost line, with mostly gas on
the inner side and mostly ice on the outer.
The protoplanetary disk, originally homogeneous, changed due to the Sun's
solar wind. Frozen volatile materials evaporated and moved beyond the frost
line, causing dust to concentrate in the inner disk and ice in the outer parts. That
caused gravity to separate the disk's materials into concentric rings with greater
density than the space between them.
3. In these rings, the material started clumping together due to gravity. When
these clumps’ diameter would exceed 1 km, a planetesimal is formed. These
kept growing progressively larger (= accretion), eventually forming
protoplanets.
4. In the inner rings, that consist mostly of refractory materials, the planets are
smaller and composed mostly of rock and metal. In the outer rings, that
consisted mostly of volatile materials, the planets have a small refractory
core that is surrounded by a big cloud of volatile materials.
Volatile materials = substances that evaporate at relatively low temperatures and can exist as gases on Earth.
Refractory materials = substances that evaporate at relatively high temperatures and usually exist as solids on Earth.
How was the Moon formed? Why is the Earth round?
It is most likely formed as a result of a collision between the Earth When the Earth started going through differentation, the core
and a protoplanet called Theia, between 4.51 Ga and 4.43 Ga. This became warm and hot enough that it could flow in response to
collision was so catastrophic that a ring of debris formed around the gravity. The ‘mountains’ were pulled inwards so that the mass would
Earth. Due to accretion, the Moon was formed. (not all moons are eventually be evenly distributed and the Earth would form a sphere.
formed this way)
How did the atmosphere and the ocean form?
Initially, the atmosphere was mostly hydrogen and helium. As temperature increased, these gases were able to escape the Earth's gravity in a
solar wind. Over time, volcanic eruptions released gases that were previously bonded to the Earth’s mantle. This led to an atmosphere primarily
composed of water, carbon dioxide, ammonia, and methane. When the Earth cooled, rain fell and oceans formed, reducing water concentration
in the atmosphere. The atmospheric CO2 dissolved in water and became solids, decreasing its concentration. As N2 doesn't react with other
Earth materials, it became the dominant component of the atmosphere. Oxygen only appeared later after organisms appeared.
Chapter 1: Cosmology 4
, Lecture
⭐ Parallax method = method to determine how far away stars are.
→ By using the distance from the Earth to the Sun, which is
about 150 million km, and the shift of the backdrop in relation
to the star, we can determine the angle and the base of a
triangle:
tan(0,0002) = 150,000,000 / x
x = 150,000,000 / tan(0,0002)
x = 40,000,000,000,000 km
Chapter 1: Cosmology 5
, 🌍
Chapter 2: Earth Structure
Journey to the Center of the Earth
2.2 Welcome to the Neighbourhood
Interstellar space = the region between stars where there Interplanetary space = the region of vacuum between
is a vacuum (= an absence of matter) where the the orbits of planets, here the concentration of atoms is
concentration is less than one atom per liter. about 5,000 - 100,000 per liter.
📏
→ The atoms that do exist in interstellar space are either
leftovers from the Big Bang or may be cosmic rays, those are 1 AU (astronomical unit) = the distance between
atomic nuclei ejected into space from supernova explosions. the Earth and the Sun = 150 million kilometres
Distance from Sun
50000 AU The Sun’s gravitational pull starts.
3500 AU The inner edge of the Oort Cloud, consisting of a vast cloud of icy planetestimals.
The outer edge of the heliosphere, (the “edge” of our Solar System) within this region there are mainly solar-wind
200 AU
particles. Outside it are mainly particles from cosmic rays
30 - 55 AU The Kuiper Belt, consisting of a cloud of mainly asteroids and some dwarf planets. The inner edge is Neptune’s orbit
2.5 AU The asteroid belt between Jupiter and Mars. It contains about 10 million objects
Most asteroids lie between the orbit of Mars and Jupiter.
Some asteroids (known as the Trojans and the Greeks)
border Jupiter’s orbit, while the Hildas lie between the
main asteroid belt and Jupiter.
The Earth has a magnetic field which is a dipole: it has 2
poles; the north pole and the south pole. A magnetic field
can be visually represented in a drawing. Here the arrows go
from the north pole to the south pole and the direction of the
lines shows how a magnetic object would turn. As can be seen in the images, the Oort Cloud is incredibly vast
The magnetic field protects the Geographic poles Magnetic poles
Earth from (potentially life-
North magnetic
threatening) particles in solar North pole Southern polarity
pole
winds, the solar wind distort the
South magnetic
shape of the field. The region South pole Northern polarity
pole
within this magnetic field is
called the magnetosphere.
Chapter 2: Earth Structure 1
, 🧲 Van Allen belts = 3000 - 10500 km from Earth, where the Earths magnetic field starts to strengthen and traps both
cosmic rays and the rest of the solar wind particles that had enough speed to penetrate the outer field.
→ Electrons that make it past the Van Allen belt stream along
the magnetic field lines and accelerate closer to the poles.
High-speed electrons interact with atmospheric oxygen and
nitrogen atoms, exciting their electrons (aangeslagen). When
these electrons return to their normal state, they emit light,
causing the gas to glow. This results in the aurorae we see.
Northern hemisphere aurorae = aurora borealis
Southern hemisphere aurorae = aurora australis
Atmosphere = the gaseous cloak that surrounds the
Earth. It consists of air, which is 78% nitrogen, 21%
oxygen and 1% other gasses. Air also contains various
amounts of H20, which at lower elevations form clouds.
The density of the atmosphere increases as you come closer
to the Earth’s surface, because of the weight of the overlaying
air. The ‘top’ of the atmosphere can be considered to be at
about 600 km away from the surface. There are so few
molecules at that height that they don’t collide and interact
like a gas does.
🌫️ At the Earth’s surface the atmosphere has a
density of 0.12 g/L or 2.7 x 10²² atoms/L . The unit
for air pressure = units of force per unit area.
People can’t survive for long at elevations above 5.5
km due to the lack of air pressure ≈ 0.5 bars.
→ Air pressure decreases with increasing elevation.
The atmosphere can be divided into different layers: the
troposphere, the stratosphere, the mesosphere and the
thermosphere. The boundaries are named for the underlying
layer.
Comets are made of ice and dust and lie generally in the
Kuiper Belt or the Oort Cloud. If take they less than 200
years to orbit the Sun they are from the Kuiper Belt, if
they take more time they are from the Oort Cloud. When
they come closer to the Sun, comets have 2 tails made
from evaporated volatile materials: the gas or ion tail
points straight away from the Sun and the dust tail
curves.
Asteroids are made from rock and lie in the asteroid belt.
2.3 Basic Characteristics of the Earth
Habitable zone = between 0.8 and 2.5 AU, where water can exist
the combinations and interactions
Earth System = in liquid form; where temperature is between 0° and 100°. This
between:
would include a bit of Venus’s and Mars’s orbit but due to the
Atmosphere the gas surrounding the Earth
abilities of their atmospheres, heat stays or escapes too easily.
Hydrosphere surface and near-surface liquid water
surface and near-surface liquid ice and
Cryosphere
snow
Biosphere the great variety of living organisms
Geosphere solid Earth
Chapter 2: Earth Structure 2
, Topography = variations in elevation. Highest point on land = Mount Everest at + 8.85 km
Lowest point on land = shore of the Dead Sea at - 0.4 km
Bathymetry = variations in the depth of the ocean floor.
Hypsometric curve = a graph that plots the surface
Continental shelves relatively shallow area bordering continents elevation on the vertical axis and the percentage of the
broad flat surfaces lying at a depth of 4 to 5 Earth’s surface on the horizontal axis:
Abyssal plains
km
Seamounts mountains that rise from the abyssal plains
shallower mountain chains that rise up to 2.5
Mid-ocean ridges
km above the abyssal plains
Deep-sea trenches deep trenches caused by subduction zones
The Earth’s surface is for 30% dry land and the remaining
70% is covered by surface water.
→ Groundwater = the water that fills holes beneath the
land surface.
Earth materials = a general term for the great variety of substances that make up this planet.
The basic categories of the elements of the earth:
Organic chemicals carbon containing compounds Methane
a naturally occurring (usually inorganic) solid substance with an internal structure characterised by
Minerals an orderly arrangement of atoms, ions or molecules. A single continuous piece of mineral grown into Quartz
shape is called a crystal.
Glass a solid in which atoms are not arranged in an orderly pattern. Glass
Melts solid materials that have melted. Lava, magma
coherent, naturally occurring solids, consisting of an aggregate of minerals or grains or a mass of
Rocks Rock
natural glass.
an individual crystal within an igneous or metamorphic rock or a fragment from a once larger
Grains -
mineral or rock.
Sediment a accumulation of loose grains that have not cemented together. Sand, gravel
Metals a solid composed entirely of metal atoms. an alloy is a mixture containing different types of metals. Iron
Volatiles materials that can exist as gasses on Earth. Oxygen
Rocks can be divided into 3 groups:
1. Igneous rock: forms when molten, liquid rock cools.
2. Sedimentary rock: forms from rock fragments that are
cemented together or from minerals that come from water
solutions near the Earth's surface.
3. Metamorphic rock: forms when pre-existing rock
undergoes changes in response to change in temperature
and pressure.
Classes of igneous rock, distinguished by composition (= SiO2 / (FeO +
91.2% of Earth’s mass consists out of: iron, oxygen, silicon MgO))
and magnesium.
Most of the Earth consists of silicate minerals (= minerals that contain silica, SiO2). If a rock contains relatively more silica it’s
called felsic or silicic, if it contains relatively less silica it’s called mafic or ultramafic.
→ Silicate rocks are rocks composed of silicate minerals.
At the Earth’s centre, pressure probably reaches about 3,600,000 atm. The temperature is estimated to be about 6000°C.
Geothermal gradient = the rate of change in temperature with depth (eg. 30°C/km).
Chapter 2: Earth Structure 3
