C1- changes in the earth and its atmosphere Flashcards
What are the three main layers of the earth (starting from the outermost) and what are their properties?
crust (relatively thin and rocky)
mantle (has the properties of a solid, but can flow very slowly)
core (made from liquid nickel and iron, consists of a solid inner core and a liquid outer core)
What is a continental drift?
The Earth’s crust and upper part of the mantle are broken into large pieces called tectonic plates. These are constantly moving at a few centimetres each year. Over millions of years the movement allows whole continents to shift thousands of kilometres apart.
Why do tectonic plates move?
The plates move because of convection currents in the Earth’s mantle. These are driven by the heat produced by the natural decay of radioactive elements in the Earth.
What happens when tectonic plates meet?
Where tectonic plates meet, the Earth’s crust becomes unstable as the plates push against each other, or ride under or over each other. Earthquakes and volcanic eruptions happen at the boundaries between plates, and the crust may ‘crumple’ to form mountain ranges.
Who proposed the theory of plate tectonics and continental drift
a German scientist, Alfred Wegener
Before Wegener, what was the theory as to why the Earth had mountains?
it was thought that mountains formed because the Earth was cooling down, and in doing so contracted. This was believed to form wrinkles, or mountains, in the Earth’s crust.
Why do we know the theory before Wegener is false?
If the idea was correct, however, mountains would be spread evenly over the Earth’s surface. We know this is not the case.
What did Wegener theorise?
Wegener suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold.
Why did it take more than 50 years for Wegener’s ideas to be accepted?
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.
What are the two main types of tectonic plates?
Oceanic plates occur under the oceans.
Continental plates form the land.
What are the differences between oceanic and continental plates?
Oceanic plates are denser than continental plates. They are pushed down underneath continental plates if they meet.
How do volcanoes form?
Magma (molten rock) is less dense than the crust. It can rise to the surface through weaknesses in the crust, forming a volcano.
Why do people choose to live near volcanoes?
The land there is very fertile.
What are the two main gases in the atmosphere?
The two main gases are both elements and account for about 99 percent of the gases in the atmosphere. They are:
78 percent nitrogen (a relatively unreactive gas)
21 percent oxygen (the gas that allows animals and plants to respire and for fuels to burn)
The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions.
How can you measure the percentage of oxygen in the air?
by passing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it. Here are the equations for this reaction:
copper + oxygen → copper oxide
How would you perform the experiment to measure the percentage of oxygen in the air?
Gas syringes are used to measure the volume of gas in the experiment. The starting volume of air is often 100 cm3 to make the analysis of the results easy, but it could be any convenient volume. You take away the volume at the end from the volume at the start to get the volume of oxygen and then work out the percentage.
What are the errors that occur with this experiment?
Note that there is some air in the tube with the copper turnings. The oxygen in this air will also react with the hot copper, causing a small error in the final volume recorded. It is also important to let the apparatus cool down at the end of the experiment, otherwise the final reading will be too high.
What was the earlier atmosphere like on earth?
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 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.
Venus and Mars today and similarities to earth?
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.
What was the aim of the Miller-Urey experiment?
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.
What happened during the Miller-Urey experiment?
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.
What theory did the Miller-Urey experiment support?
The Miller-Urey experiment supported the theory of a ‘primordial soup’, the idea that complex chemicals needed for living things to develop could be produced naturally on the early Earth.
Why did the level of oxygen in the atmosphere increase?
The appearance of plants and algae caused the production of oxygen, which is why the proportion of oxygen went up due to photosynthesis.
Why did the level of carbon dioxide go down?
Photosynthesis by plants and algae used carbon dioxide from the atmosphere.
dissolving in the oceans
the production of sedimentary rocks such as limestone
the production of fossil fuels from the remains of dead plants and animals
How is nitrogen and oxygen separated?
by fractional distillation of liquid air
How do you liquify 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
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.
How does fractional distillation separate the liquid air?
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.
What are the uses of nitrogen and oxygen?
liquid nitrogen is used to freeze food
food is packaged in gaseous nitrogen to increase its shelf life
oil tankers are flushed with gaseous nitrogen to reduce the chance of explosion
oxygen is used in the manufacture of steel and in medicine.
