Earth Formation and History Flashcards
1
Q
When was the big bang?
A
14 billion years ago
2
Q
What happened in the big bang?
A
- Universe expands very quickly
- Atoms started forming 13.8 seconds after the big bang
- our solar system formed from a Solar Nebular
3
Q
What is a nebula and how does our solar system relate to it?
A
- A nebula cloud made from a collection of dust and gas. It is believed that the sun, planets, moons, and asteroids were formed around the same time around 4.5 billion years ago from a nebula
4
Q
What is the Nebular Theory?
A
- Proposed by Thomas Wright in 1700’s
- Solar systems form by condensation of molecular gas and dust into a large cloud (Nebular Cloud)
- The cloud starts to spin as gravity pulls more material in
- As it gets denser it collapses in itself but the spinning motion continues, so the object becomes a disk
5
Q
Where in our galaxy is the Earth
A
- 26 000 light years away from the centre of the milky way
6
Q
What was the cause of the big bang?
A
- An ancient star exploded, littering space with swirling clouds of the materials (star dust) it had made while it lived and the heavier metals it created as it died
7
Q
How do we know that the big bang was created by an exploding star?
A
- Evidence of similar fields of dust, out in space today, have been found
- They are called nebulae
8
Q
Are nebulae unique?
A
- Every nebula is different
- Our nebula contained nitrogen, oxygen, iron, silica and all the other stuff needed to build a world like ours
9
Q
What happened after the nebulae were formed?
A
- Gravity started to pull the nebula back together from the explosion
- This caused the engineering that produces planets to begin
- Vast spirals of began to form and at the centre of one of these, a rocky planet called Earth started to take shape
10
Q
What happens to the spirals of star dust that started to create the planets?
A
- at the centre of one of the spirals, Earth was being formed
- 100 years later and it had grown into a giant ball, sweeping up tons of celestial debris
- This is where the Earth came from
11
Q
How was Earth able to support life?
A
- Our planet would have remained a large, sterile ball of rock, metals and minerals forever, were it not for the sun.
12
Q
How did the sun from
A
- 93 million miles away at the heart of the giant nebula, the pressure and temperature of a ball of hydrogen gas had become so great that the atoms were beginning to fuse
- The new star, the sun, was coming to life and as it ignited it gave off a huge blast of solar wind.
13
Q
What was the effect of the solar wind generated by the ignition of the sun?
A
- the radioactive gust of energy blew all the remaining dust and gas from the nebula out to the edge of the solar system
- This is why everything is nice and orderly today
14
Q
Why is everything nice and orderly because of the solar wind from the sun?
A
- Since the solar wind blew the remaining star dust to the edge of the solar system it created an orderly arrangement of the planets
- E.g. In the outer reaches of the solar system we have gas planets like Jupiter, Saturn, Uranus and Neptune. Further in are the denser, rockier planets such as Mercury, Venus, Mars and Earth
15
Q
What makes our planet so special in its placement?
A
- The sun is 865 000 miles in diameter and 93 million miles away
- This makes it perfect for our planet because it burns consistently for a very long time (8 billion years)
- This is long enough to allow the next development to take place, life.
16
Q
What happened to the remaining dust from the nebula that was blown to the edge of the solar system?
A
- Remaining masses of particles and dust less than 200 m in diameter started pulling together under their own gravity through a process called accretion
- These masses of particles are baby planets -> planetesimals
- They kept growing and fully formed about 4.5 billion years ago
17
Q
What is the order of the planets from the sun?
A
Sun -> Mercury -> Venus -> Earth -> Mars -> Jupiter -> Saturn -> Uranus -> Neptune
18
Q
What are the features of Pluto that are considered when debating whether it is a planet?
A
- It’s really far from the sun – more than 3 billion km
- It’s tiny, diameter is smaller than width of Australia
- It’s made mostly of ice and rock
- It has 5 moons
- 1 Pluto day is about 6.5 Earth days
19
Q
What are the three criteria for a planet to be a planet?
A
1) Be spherical
2) Rotate only around the sun and no other body as well (which rules out larger moons)
3) Have ‘cleared out its area of other space debris’ - Pluto hasn’t done this, it’s packed in with comets and asteroids that orbit the sun
20
Q
What caused the inner, rocky planets to form?
A
- In close to the sun, the high temperature condensates (nickel, iron, silicates) accreted and formed the inner rocky planets
- Terrestrial Planets (rocky, dense with density ~4-5 g/cm3)
21
Q
What caused the outer, gas planets to form?
A
- Out further, light pressure or stellar wind from the newly formed sun blows away low temperature condensates from the inner planets, creating differentiation between the rocky planets and the gas giants
- Jovian Planets (light, gassy, H, He, density 0.7-2)
22
Q
What is a Heritable Zone?
A
- Where in the solar system water can exist
- Only Earth is in the Heritable Zone for our solar system
23
Q
Why is Earth so special?
A
- Earth, the third planet from the Sun
- Currently the only planet known to support life.
- Earth’s distance from the Sun is thought to be one of the key reasons why it is home to widespread life (150 million kilometres).
- Our planet occupies what is sometimes call the Goldilocks zone. Its distance from our star means it is neither too hot, nor too cold to support liquid water.
24
Q
What is the Differentiation of earth?
A
- The Earth is thought to have commenced as a homogenous mixture of molten rock and gases
- During the process of differentiation, iron sank to the centre of the Earth and light material floated upward to form a crust, and as a result, the Earth is now a stratified planet with different layers, but is still undergoing differentiation as it cools down.
25
Study the Diagrams of the Order of the Planets, The Density of the Planets, The Habitable Zone and The Differentiation of Earth
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
26
What is the density of the different layers of the Earth?
- Crust = 3 g/cm^3
- Mantle = 4 g/cm3
- Outer Liquid Core = 10 g/cm3
- Inner Solid Core = 13 g/cm3
27
What was the effect of Differentiation of the Earth?
- Differentiation has created a light crust (relatively) depleted of iron, but rich in oxygen, silicon, aluminium, calcium, potassium and sodium.
- Differentiation also led to the formation of Earth’s atmosphere and oceans (helped along with material from comets)
28
How do we know how old the Earth is?
- We use geo-clocks which contain radioactive elements which decay at known rates
- E.g. Half lives of isotopes
29
What do Geo-Clocks use to date the Earth's age?
- We need to find compounds on the Earth where we can apply this decay theory
- Minerals called zircons are perfect
- They are tiny little crystals that form when magma cools
- When they crystallise, they lock out lead
- So the only way they contain lead is by uranium decay
30
What is the Decay Equation?
- We need to know how to use decay rates to figure out how old a part of the Earth is.
- The Decay Equation:
N(t) = N0 x e^-kt
Where:
- N(t) = The proportion of the parent isotope at a given time,
- N0 = The proportion of the parent isotope at time zero (i.e., 1)
- e = 2.71,
- k = decay constant
- t = time in billions of years
31
How is the Decay Equation rearranged?
- We can rearrange the equation so we can figure out how old something is based on measured concentrations:
T = ln[N(t)/N0] x -k^-1
32
A rock sample collected from outback Queensland has zircon crystals whose uranium concentration is 0.99 of its combined uranium+lead concentration. How old is the rock? P.s. K for U decay to Pb = 0.15
- T = ln[N(t)/N0] x -k^-1
- T = ln(0.99/1) x -0.15^-1
= 67 million years
33
How old are some of the oldest zircon crystals?
- Some zircon crystals are very old = 4.4 billion years
| - The oldest rocks found yet were in Western Australia
34
What are some Geo-cocks other than Uranium to Lead?
- Potassium to Argon
- Beryllium to Boron
- Chlorine to Argon
- Carbon to Nitrogen
The table of these Radiometric clocks is found in the google doc
35
What is Geological History?
- We know the Earth is very old (about 4.5 billion years)
| - Geological history or geological time tells us the ancient history of the Earth from its formation to today
36
How are the time scales of Geological History broken up?
- Time scales are broken up into different horizons
- EON = billion yr scale
- ERA = 10’s million year scale
- PERIOD = million yr scale
- EPOCH = 1,000s yr scale
37
Study the Diagrams of the components of the Earth, Half life of Uranium, The Decay Equation, The Geological History Table
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
38
When did dinosaurs appear?
- 250 million years ago
39
When was the largest mass extinction event?
- 255 million years ago
40
When did humans appear?
- 200 000 years ago
41
When did life on Earth begin?
3.3 billion years ago
42
When did the Earth form?
4.5 billion years ago
43
What is believed to be the first organisms from 3.3 billion years ago at the start of life on earth?
- The first organisms are thought to be cyanobacteria – sometimes called blue-green algae
- Emerged during the Archean Eon
- Single cell prokaryote organisms that can photosynthesise
- They don’t have chloroplasts but they are believed to be the precursors to chloroplasts in plants
- Responsible for oxygenating the Earth
44
What caused the rise of complex life?
- Not much happened for the rest of the Archean and through the Proterozoic Eons
- Then, about 500 million years ago, complex life exploded into existence
- This was the start of the Cambrian Period in the Palaeozoic Era in the Phanerozoic Eon
- Multicellular organisms, some with hard shells
45
What Era was the age of the dinosaurs in?
- The Mesozoic Era
46
Which periods did the Mesozoic Era encompass?
- Triassic Period (250 - 180 MYA)
- Jurassic Period (180 - 120 MYA)
- Cretaceous Period (120 - 60 MYA)
