Alfred Wegener (1880 - 1930)
Wegener's evidence for continental drift was that:
* the same types of fossilised animals and plants are found in South America and Africa
* the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle
* matching rock formations and mountain chains are found in South America and Africa
Why wasn't Wegener's theory not accepted for million of years.....?
It took more than 50 years for Wegener’s theory to be accepted. One of the reasons was that it was difficult to work out how whole continents could move: it was not until the 1960s that enough evidence was discovered to support the theory fully.
2. The single land mass began to crack and divide, due to the slow currents of magma beneath it.
1. Earth around 200 million
years ago, at the time of
Pangaea.
3.The position of the continents today
Volcanoes and Earthquakes....
First of all there are two main types of tectonic plates:
* Oceanic plates occur under the oceans
* Continental Plates form the land
Oceanic plates are denser than continental plates. They are pushed down underneath continental plates if they meet.
So how do volcanoes occur.......?
Where tectonic plates meet, the Earth’s crust becomes unstable as the plates slide past each other, push against each other, or ride under or over one another.
Earthquakes and volcanic eruptions happen at the boundaries between plates. They occur at destructive (compressional) and constructive (tensional) plate boundaries. Magma (molten rock) is less dense than the crust. Volcanoes form when magma reaches the Earth's surface, causing eruptions of lava and ash. It can rise to the surface through weaknesses in the crust, forming a volcano.
Geologists study volcanoes to try to predict future eruptions. Volcanoes can be very destructive, but some people choose to live near them because volcanic soil is very fertile.
The formation of volcanoes:
1. 2. Magma rises through cracks or weaknesses in the Earth's crust.
3. Pressure builds up inside the Earth.
4. When this pressure is released, as a result of plate movement, magma explodes to the surface causing a volcanic eruption.
5. The lava from the eruption cools to form new crust.
6. Over time, after several eruptions, the rock builds up and a volcano forms.
So how do Earthquakes occur.......?
Earthquakes are caused by the release of built-up pressure inside the Earth's crust. An earthquake's power is measured on the Richter Scale using an instrument called a 'seismometer'.
The effects of an earthquake can be devastating - they can destroy settlements, change landscapes, and cause many deaths.
An earthquake is the shaking and vibration of the Earth's crust due to movement of the Earth's plates (plate tectonics). Earthquakes can happen along any type of plate boundary.
Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.
If the plates are moving sideways, stresses build up at the plate boundary. When the stress reaches some critical value, the plates slip suddenly, causing an earthquake.
Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.
The point inside the crust where the pressure is released is called the focus. The point on the Earth's surface above the focus is called the epicentre. Earthquake energy is released in seismic waves. These waves spread out from the focus. The
waves are felt most strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an earthquake will happen close to the epicentre.
Why can't Volcanoes and Earthquakes be predicted?
Volcanoes and Earthquakes depend on the interactions of the motions of plates, the pressure of magma in different places far underground etc. All of this is buried so deep in the earth that we can't measure it with sufficient resolution to tell what is really happening, let alone what will happen in the future.
The Composition of the Earth's atmosphere Today:
The Earth's atmosphere has remained much the same for the past 200 million years. The pie chart shows the proportions of the main gases in the atmosphere. It is clear that the main gas is nitrogen. Oxygen is the next most abundant gas. These two gases are both elements and account for about 99% of the gases in the atmosphere. They are:
about 4/5 or 80 percent nitrogen (a relatively unreactive gas)
about 1/5 or 20 percent oxygen (the gas that allows plants and animals to respire)
The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions.
What events caused the Earth's Early Atmosphere billions of years ago?
Scientists believe that the Earth was formed about 4.5 billion years ago. Its early atmosphere was probably formed from the gases given out by volcanoes. It is believed that there was intense volcanic activity for the first billion years of the Earth's existence. The activity that released the gases that formed the early atmosphere and water vapour that condensed to form the oceans.
The Composition of the Earth's Early atmosphere:
The early atmosphere was probably mostly carbon dioxide, with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth.
Scientists can’t be sure about the early atmosphere and can only draw evidence from other sources: for example, volcanoes on other planets release high quantities of carbon dioxide or nitrogen and iron-based compounds which are present in very old rocks that could have formed only if there was little or no oxygen.
It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth.
The table shows the proportions of the main gases in their atmospheres.
Gas
Mars today
Venus today
________________
carbon dioxide
________________
95.3
96.5
________________
nitrogen
________________
2.7
3.5
________________
argon
________________
1.6
trace
________________
oxygen, water vapour and other gases
________________
trace
trace
How were Oceans made?
As you should know from previously the early atmosphere of the Earth was probably mainly carbon dioxide with either little or no oxygen. There was also smaller proportions of water vapour, ammonia and methane. As the Earth cooled down,most of the water vapour condensed and formed the oceans.
Miller Urey Experiment:
There is evidence that the first living things appeared on Earth billions of years ago. There are many scientific theories to explain how life began. One theory involves the interaction between hydrocarbons, ammonia and lightning.
Stanley Miller and Harold Urey carried out some experiments in 1952 and published their results in 1953. The aim was to see if substances now made by living things could be formed in the conditions thought to have existed on the early Earth.
The two scientists sealed a mixture of water, ammonia, methane and hydrogen in a sterile flask. The mixture was heated to evaporate water to produce water vapour. Electric sparks were passed through the mixture of water vapour and gases, simulating lightning. After a week, contents were analysed. Amino acids, the building blocks for proteins, were found.
So what is the significance of the Miller-Urey Experiment......
The Miller-Urey experiment is a very important experiment as it proved that life can come from chemicals. This experiment was successful in providing the first real evidence for a theory on how life on Earth began.
It supported a hypothesis that life originated on Earth due to the presence of inorganic chemicals and an energy source.
The Primordial Soup Theory:
The primordial soup theory suggests that life began in a warm pond from a combination of chemicals that formed amino acids, which then ended up creating proteins. This has been said to have happened at least 3.8 billion to 3.55 billion years ago.
The Primordial Soup Model is the mix of gases in water that were present at the time of early earth that when electrically charged (simulated lightning), created basic organic molecules, such as amino acids- some of the basic building blocks for proteins and enzymes- that eventually led to the formation and creation of life on Earth. This is only a hypothesis for the origin of life, and is but one of many other possible beginnings for life on this planet preceding evolution. This hypothesis is backed by the Miller-Urey experiment, proving that, with fairly simple conditions similar to those projected to have existed sometime over 4 billion years ago, life's most basic and fundamental compounds could be synthesized proving it possible and perhaps likely that early Earth supported conditions necessary for spontaneous generation (something now impossible). This however, cannot be confirmed as there is no way of knowing exactly how life got its start.
How did Oxygen get into the atmosphere?
Early bacterial life introduced oxygen to the atmosphere. As the first free oxygen was released through photosynthesis by cyanobacteria, it was initially soaked up by iron dissolved in the oceans and formed red coloured iron oxide, which settled to the ocean floor. Over time, distinctive sedimentary rocks called banded iron formations were created by these iron oxide deposits. Once the iron in the oceans was used up, the iron oxide stopped being deposited and oxygen was able to start building up in the atmosphere about 2.4 billion years ago.
Where can the Carbon Dioxide in the atmosphere go?
Carbon Dioxide is not only used by plants and algae for photosynthesis but it is also used by many other processes which absorb carbon dioxide from the atmosphere.
Most of the carbon from the carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels.
The oceans also act as a reservoir for carbon dioxide but increased amounts of carbon dioxide absorbed by the oceans has an impact on the marine environment.
Nowadays the release of carbon dioxide by burning fossil fuels increases the level of carbon dioxide in the atmosphere.
Why are the levels of Carbon Dioxide rising in the atmosphere?
Humans burn fossil fuels such as oil, coal and natural gas. The energy released is used to power cars and other machines, to generate electricity, and to keep buildings warm. The burning fuel releases waste gases, including carbon dioxide. As the human population increases, more fuel is used, and more carbon dioxide is released.
The fossil fuels include coal, natural gas and the products from the fractional distillation of crude oil, such as petrol and diesel. When any fossil fuel is burned, one of the combustion products is carbon dioxide.
Over the past 100 years, increasing amounts of fossil fuels have been burned each year. This has led to an increase in the percentage of carbon dioxide in the air.
How can fractional distillation be used to provide a source of raw materials?
You will recall that about 78 percent of the air is nitrogen and 21 percent is oxygen. These two gases can be separated by fractional distillation of liquid air.
Liquefying the air
Air is filtered to remove dust, and then cooled in stages until it reaches –200°C. At this temperature it is a liquid. We say that the air has been liquefied.
Here's what happens as the air liquefies (note that you do not need to recall the boiling points of the different gases):
* water vapour condenses, and is removed using absorbent filters
* carbon dioxide freezes at –79ºC, and is removed
* oxygen liquefies at –183ºC
* nitrogen liquefies at –196ºC.
The liquid nitrogen and oxygen are then separated by fractional distillation.
Fractional distillation
The liquefied air is passed into the bottom of a fractionating column. Just as in the columns used to separate oil fractions, the column is warmer at the bottom than it is at the top. The liquid nitrogen boils at the bottom of the column. Gaseous nitrogen rises to the top, where it is piped off and stored. Liquid oxygen collects at the bottom of the column. The boiling point of argon - the noble gas that forms 0.9 percent of the air - is close to the boiling point of oxygen, so a second fractionating column is often used to separate the argon from the oxygen.
________________
[1]There is a difference between Tectonic Plates and Plate Tectonics. Tectonic plates are the pieces of the Earth's crust and the upper part of the mantle. Whereas Plate tectonics is how the tectonic plates move, part of the Earth's Crust move and the theory of that.