Earth
Introduction
We live on planet Earth. A planet made mainly of iron and other metals. It has a relatively thick atmosphere of Nitrogen and Oxygen. The surface is around 70% water and 30% land. Factoring in the greenhouse gases of its atmosphere, Earth is at just the right distance from its star, The Sun, for water (H2O) to be a liquid... not too cold to be solid ice, but too hot to evaporate into gas. If the Earth had no atmosphere, all the water would freeze.
Today, the Earth is host to a wide variety of forms called life, collections of molecules that can make copy of themselves. These forms defy the natural tendency of things in the universe to go from ordered structure to a form random and mixed. Life has existed on Earth for the last 3.5 billion years, but only on land for around half a billion years. Life on land possible has not even 500,000 million years to go (0.5 billion) before the sun's increased energy output causes the atmosphere to dramatically change and for the oceans to evaporate (http://www.sciencedaily.com/releases/2013/12/131216142310.htm).
Size of Earth
Earth has a circumference (e.g. how far you go if you run a full lap around the equator) of 40,000 km. It would take 17 days of non-stop driving at 100 km/hour to travel this distance!
We live on planet Earth. A planet made mainly of iron and other metals. It has a relatively thick atmosphere of Nitrogen and Oxygen. The surface is around 70% water and 30% land. Factoring in the greenhouse gases of its atmosphere, Earth is at just the right distance from its star, The Sun, for water (H2O) to be a liquid... not too cold to be solid ice, but too hot to evaporate into gas. If the Earth had no atmosphere, all the water would freeze.
Today, the Earth is host to a wide variety of forms called life, collections of molecules that can make copy of themselves. These forms defy the natural tendency of things in the universe to go from ordered structure to a form random and mixed. Life has existed on Earth for the last 3.5 billion years, but only on land for around half a billion years. Life on land possible has not even 500,000 million years to go (0.5 billion) before the sun's increased energy output causes the atmosphere to dramatically change and for the oceans to evaporate (http://www.sciencedaily.com/releases/2013/12/131216142310.htm).
Size of Earth
Earth has a circumference (e.g. how far you go if you run a full lap around the equator) of 40,000 km. It would take 17 days of non-stop driving at 100 km/hour to travel this distance!
Land Water Ratio
Around 70% of the Earth’s surface is water with less than 30% being land.
Around 70% of the Earth’s surface is water with less than 30% being land.
Age and Birth
Earth is 4.54 billion years old. It is the same age as the sun and the rest of the solar system.
It formed from a spinning gas cloud that collapsed. Most of the cloud collapsed into the centre to form the sun. Some dust grains had enough speed to not fall in. They collided and collided, accumulating mass until they formed the planets.
Earth is 4.54 billion years old. It is the same age as the sun and the rest of the solar system.
It formed from a spinning gas cloud that collapsed. Most of the cloud collapsed into the centre to form the sun. Some dust grains had enough speed to not fall in. They collided and collided, accumulating mass until they formed the planets.
The Earth Over Time
The Earth has not always been like it is today. Here are some key events in the history of the Earth.
The Earth has not always been like it is today. Here are some key events in the history of the Earth.
Layers of the Earth
The Earth isn’t a homogenous ball of one material. The Earth has layers.
The Earth isn’t a homogenous ball of one material. The Earth has layers.
The outer layer (the shell if you will) is called the crust. The next level is is called the mantle (made of liquid rock). The innermost sections are called the outer core (liquid) and inner core (solid).
Below shows a cross triangular cut out of part of the Earth, to show what the layers of the Earth look like for us on the surface as we look down.
Earth’s Magnetic Field
The molten iron outer core is believed to be responsible for the Earth being like a giant magnet. As the iron spins, it causes the Earth to generate a magnetic field. The magnetic field extends all the way out into space:
This magnetic field is able to protect us (on the surface of Earth) from the dangerous solar wind coming from the Sun. It is able to deflect the charged up solar wind.
Plate Tectonics
The Earth’s crust is not one solid unit… it’s made up of multiple plates… each of which is separate from the others. These plates move, each in their own way, causing volcanoes, earthquakes, tsunamis, and constantly changing the appearance of Earth.
Below shows a globe of the Earth and how the crust is 'cracked' into plates.
Interaction Between Plates
Tectonic Plates can interact with each other in 3 ways:
Tectonic Plates can interact with each other in 3 ways:
- Converge (come together)
- Diverge (move apart)
- Transform (slide past each other)
Why do the plates move?
The answer is Convection Currents. The heat rising from the Earth's core creates convection currents in the plastic layer of the mantle (asthenosphere). The convection currents slowly move the tectonic plates above them in different directions. Convection currents occur because hot fluids are less dense than cold fluids. The hot rock rises and the cooler rock sinks due to gravity (From Mission to Mars site).
The Earth's crust is broken up into tectonic plates (not unlike a cracked egg-shell). The direction the plates moves depends upon where they sit above convection currents.
Diverging Boundaries
Rising convention currents push the plates apart at divergent boundaries. New rocks are formed as magma rises to the surface and solidifies deep in the ocean. This is known as sea-floor spreading.
Converging Boundaries
Plates are pushed together at convergent boundaries.
Plates are pushed together at convergent boundaries.
- When continental crust collides with continental crust the land is pushed upwards to form huge mountains (eg. Himalayas).
- Where oceanic crust collides with continental crust, the oceanic crust is forced downwards under the continental crust. This is called a subduction zone.
Transformation Boundaries
Some plates slide past each other at transformation boundaries
How do we know about the Earth's Interior?
Earthquakes and the seismic waves they produce allow us to learn about the Earth's Interior. Go to the following link from the Mission to Mars site to learn more: https://sites.google.com/site/missiontomarsatvssec/home/mission-background-briefing-students/earth-vs-mars/earthquakes
Earth's Atmosphere
The Earth’s atmosphere is always changing. However, we can divide the Earth’s atmosphere into three different periods:
Earthquakes and the seismic waves they produce allow us to learn about the Earth's Interior. Go to the following link from the Mission to Mars site to learn more: https://sites.google.com/site/missiontomarsatvssec/home/mission-background-briefing-students/earth-vs-mars/earthquakes
Earth's Atmosphere
The Earth’s atmosphere is always changing. However, we can divide the Earth’s atmosphere into three different periods:
- The early atmosphere
- The atmosphere before photosynthesising plants
- The current atmosphere
You can learn more about the atmosphere's formation here: http://scijinks.jpl.nasa.gov/atmosphere-formation/
Today the atmosphere is made up of the following proportion of gases:
Today the atmosphere is made up of the following proportion of gases:
Notice that nearly 80% of the atmosphere is Nitrogen. Nitrogen is an inert gas that doesn't react very easily. Oxygen makes up around 21% of the atmosphere, and is the most important gas in the atmosphere for living things.
Particle Distribution in the atmosphere
The Earth’s gravity pulls more of the gas particles closer to the surface. The density is not uniform:
Particle Distribution in the atmosphere
The Earth’s gravity pulls more of the gas particles closer to the surface. The density is not uniform:
Note there are more particles at the bottom than at the top. This is because on a large scale, the effect of gravity pulling everything towards the centre of the Earth is noticeable. In a classroom, there is no noticeable difference between air near the roof and air near the ground. However, there is a noticeable difference between air in Melbourne and at Mount Everest. As the air is 'thinner' at Mount Everest, the oxygen is more spread out, and so it is harder to get the same amount of oxygen into your blood to process properly. Thus climber's often take oxygen tanks to help them.
Layers of the Atmosphere
The atmosphere is divided into layers. One set of layers uses temperature variation as divisions.
Layers of the Atmosphere
The atmosphere is divided into layers. One set of layers uses temperature variation as divisions.
The layers are all called spheres because when seen from space, they are actually spherical layers like that of an onion:
Although heights are sometimes given as to where one layer ends and another begins, these are only ball park figures. There are no exact heights at which it changes. The change occurs due to the temperature variation. The Troposphere is a ‘cooling as you go higher’ layer. Once the temperature starts increasing with altitude you are in the Stratosphere, a ‘heating as you go higher’ layer. The next layer of course is a ‘cooling as you go higher’ layer called the Mesosphere. The next layer of course is a ‘heating as go higher’ layer called the Thermosphere. The red line on the image below shows temperature. The more to the right it is, the hotter the temperature is at that height/altitude. The more to the left it is, the colder the temperature is at that height/altitude.
Greenhouse Gases (Optional)
The Earth absorbs some of the sun's heat (reflects some too) and this heats up the Earth. Like all things, the Earth emits heat too.
The amount of direct sunlight the Earth absorbs is actually not enough to keep water a liquid. The Earth needs some extra energy to keep things warm enough for liquid water. Luckily, the Earth's atmosphere has a small amount of greenhosue gases like water vapour, carbon dioxide, and methane, which trap some of the heat the Earth emits and sends it back down to the Earth. This keeps the temperature at the surface of the Earth at a good temperature for water to stay a liquid. If we had no greenhosue gases, the world would freeze over.
However, if we had 1000 times more greenhouse gases, too much heat would be trapped and the Earth would warm too much and our liquid water would evaporate into a gas. Keeping the Earth in its current state requires just the right amount of greenhouse gases.
The Earth is very dynamic and always changing. Every year billions of tonnes of greenhouse gases naturally find their way to the atmosphere through volcanoes and decaying dead things etc. But at the same time, billions of tonnes of greenhouse gases are naturally absorbed by plants and the oceans and are taken away from the atmosphere. There is a fine balance at work with the amount coming in roughly equalling the amount going out. It is kind of like a bathtub full of water. The tap is on and water is constantly falling into the bathtub. Luckily the plug is out, and a large amount of water is constantly doing down the drain. 100 years ago, the Earth's greenhouse gas situation was like this bathtub. The amount of water was just right, and the amount falling in was equal to the amount going out.
Today, humans have contributed to the situation. Humans today add greenhouse gases (mainly carbon dioxide) to the atmosphere every time they burn coal for electricity or burn fuel for cars and aeorplanes. Whilst the amount humans add is small comparative to the total already in there, and even the flow rate in and out from natural processes... the human influence is noticeable. To return to our bath analogy, the human involvement is like hanging a wet dripping towel over the bath. Each little drip on its own isn't much. But each drip is effecting the balance, and causing the water level to rise. Because of a few drips, constantly adding, the water is rising and is about to overflow. For Earth, the greenhouse gas levels are rising just enough to cause the surface temperatures to rise. This can have lots of effects on ecosystems, ocean currents, and our own comfort.
Some people think that the formula is simple: if this is really happening, then the temperature should always be much hotter in Melbourne. But its more complicated than that. All the extra greenhouse gases do is put more energy into our lower atmosphere. How that extra energy manifests itself can be in a range of ways: more cyclones and storms; longer and harsher droughts; more flooding. Giving the atmosphere more energy gives it the ability to DO MORE. And when the atmosphere stops just being relaxed and starts doing things, its normally bad for humans.
Life on Earth (Optional)
Life on Earth seemed to arise quite early in Earth's history, when it was less than 1 billion years old.
Life on Earth started off very simply, as organic molecules (molecules made mainly from carbon that is) began to make copies of themselves.
Once life began, it remained simple for a very long time. But slowly but surely, mutations caused by radiation caused new copies to have defects... when the defects proved to be an advantage, the defected copies were able to survive to make copies of themselves. From this, life began to diversify. Since then, a process called evolution by natural selection has seen defected copies that are more suitable to the environment survive and make copies of themselves too (the old non-defected copies could also make copies of themselves too). Today we understand that all living things came from the same ancestors. That is, if you were to line your mum, your grandmother, your great grandmother, her mum, and her mum again, etc. etc. (just keep putting one mum after the next) in a long line and trace it back, eventually you would find you have a great great great grandmother that isn't human. More amazingly, if a dog were to do the same thing with its mum and grandmother etc., eventually the 2 lines would meet, and you and the dog would share a common ancestor, a shared great great great (etc.) grandmother!!! And its not only with dogs but with trees too. You and a tree have a common ancestor!!! And not even trees... bacteria too!!! In fact, you share a common ancestor with all living things. With other humans, you only have to go back 2 million years at most... with monkeys... only around 10 million years... for dogs and other mammals, only 70 million years... for trees you have to go back billions of years... and for bacteria, practically to the start of life.
SHORT ACTIVITIES:
1. Demonstrate statistically that the Earth is 70% water and 30% land. (HANDS ON)
What to do: Find a globe of the Earth that is soft and not attached to anything (so its like a ball). With a friend or friends, throw the ball back and forth to each other. Each time you catch it, observe where your right index finger lands (any finger will do). If its on 'water', mark down water, if its on 'land' mark down land. Do this 50-100 times, making sure you throw it with enough spin and varying rotation to mimic randomness. Each time record 'Land' or 'Water'. At the end, add up the results and see if you get close to a 7:3 ratio.
NEED: A soft ball with the Earth on it.
2. Plate Tectonic Tennis Ball Globe (HANDS ON)
A template of the Earth divided into its tectonic plates is given to you on one the following PDFs. Print it out and colour the plates in different colours. Then cut it out and stick it onto a tennis ball. Then you have a globe with tectonic plates. The school has a soccer ball version too, but if you bring a tennis ball in yourself, you get to keep it!!!
NEED: A tennis ball
Template for you to colour in: http://volcanoes.usgs.gov/about/edu/dynamicplanet/ballglobe/ballglobe.pdf
Template already coloured in: http://www.ga.gov.au/corporate_data/68913/68913.pdf
Below is a picture of the top one coloured in:
1. Demonstrate statistically that the Earth is 70% water and 30% land. (HANDS ON)
What to do: Find a globe of the Earth that is soft and not attached to anything (so its like a ball). With a friend or friends, throw the ball back and forth to each other. Each time you catch it, observe where your right index finger lands (any finger will do). If its on 'water', mark down water, if its on 'land' mark down land. Do this 50-100 times, making sure you throw it with enough spin and varying rotation to mimic randomness. Each time record 'Land' or 'Water'. At the end, add up the results and see if you get close to a 7:3 ratio.
NEED: A soft ball with the Earth on it.
2. Plate Tectonic Tennis Ball Globe (HANDS ON)
A template of the Earth divided into its tectonic plates is given to you on one the following PDFs. Print it out and colour the plates in different colours. Then cut it out and stick it onto a tennis ball. Then you have a globe with tectonic plates. The school has a soccer ball version too, but if you bring a tennis ball in yourself, you get to keep it!!!
NEED: A tennis ball
Template for you to colour in: http://volcanoes.usgs.gov/about/edu/dynamicplanet/ballglobe/ballglobe.pdf
Template already coloured in: http://www.ga.gov.au/corporate_data/68913/68913.pdf
Below is a picture of the top one coloured in:
LONGER ACTIVITIES
1. Determine the circumference of the Earth (HANDS ON)
By using a combination of real measurements made outside and using Starry Night software to get a measurement in Cairns, you can find the size of the Earth!!! To learn more, go to http://radiusofearth.weebly.com
2. Watch the documentary "The History of the Earth"
This 1 hour 30 minute documentary looks at the birth of the Earth and how the Earth has changed over time, including the beginning of life, the first humans, the forming of the oceans, the snowball Earth, the changing continents etc. etc.
3. Greenhouse Gases Investigation
Using a pHet simulator (http://phet.colorado.edu/en/simulation/greenhouse) complete an activity investigating the greenhouse effect.
The Investigation is here: http://www.avilafm.com/greenhouse.pdf
1. Determine the circumference of the Earth (HANDS ON)
By using a combination of real measurements made outside and using Starry Night software to get a measurement in Cairns, you can find the size of the Earth!!! To learn more, go to http://radiusofearth.weebly.com
2. Watch the documentary "The History of the Earth"
This 1 hour 30 minute documentary looks at the birth of the Earth and how the Earth has changed over time, including the beginning of life, the first humans, the forming of the oceans, the snowball Earth, the changing continents etc. etc.
3. Greenhouse Gases Investigation
Using a pHet simulator (http://phet.colorado.edu/en/simulation/greenhouse) complete an activity investigating the greenhouse effect.
The Investigation is here: http://www.avilafm.com/greenhouse.pdf