The Evolution of the Atmosphere Learning Objectives: Describe the early atmosphere and the origins of the gases Explain how the atmosphere has changed Relate these changes to life processes.
Our Atmosphere Use the words given below to construct word equations for photosynthesis and respiration. You will need to use some of them more than once. carbon dioxide oxygen water glucose releases energy chlorophyll light energy Photosynthesis ……………………... + …………….……….. ………………….….. + …………….……….. Respiration ……………………... + …………….……….. ………………….….. + …………….………..
No atmosphere detected 4.2 billion years ago The Earth – all rock and volcanoes, no real atmosphere at all. The planet is cooling and solidifies as heat radiates into space.
Oxygen conc 0.000% 4 billion years ago Intense volcanic activity releases nitrogen, carbon dioxide, hydrogen and water vapour to make a fairly dangerous atmosphere. The atmosphere is very dense, the atmosphere is too hot for liquid water to form.
Oxygen conc 0.001% 3.2 billion years ago After the intense volcanic activity it began to rain (constantly for over a million years!) and the oceans formed. Tiny photosynthetic bacteria evolved. They give out oxygen as a waste product and its concentration in the atmosphere is slowly increased. They also make nitrogen from ammonia.
Oxygen conc 2.1% 400 million years ago Oxygen concentration now at 10% of modern day levels. Land plants start to appear and they produce even more oxygen. Some of the older bacteria are starting to die out. They evolved in a time with no oxygen and they are damaged by the rise in oxygen levels.
Oxygen conc 21.0% AD 2009 Oxygen levels are stabilised at about 21% of the atmosphere. The oxygen level hasn’t changed for 200 million years.
Summary Volcanoes added carbon dioxide, ammonia, methane, and water vapour to the atmosphere. Bacteria begin to photosynthesize which decreases the amount of carbon dioxide and increases the amount of oxygen in the atmosphere. The oxygen reacts with ammonia from volcanoes to add nitrogen to the atmosphere. Multi-celled plants evolved which adds even more oxygen to the atmosphere. More nitrogen is added as plants decay and are consumed by denitrifying bacteria.
Atmospheric Carbon Dioxide Concentration • How can you explain • The rise in carbon in the atmosphere since 1960? • The up and down movements on the graph? Long-term trend Monthly mean 1960 1970 1980 1990 2000 Year
The Noble Gases • Locate noble gases in the periodic table • List the elements in group 8 (or 0) • Relate the properties of the Noble gases to their uses.
4 He 2 Discovered : by Sir William Ramsay in 1895Origin : The name is derived from the Greek ‘helios’, sunDescription : A colourless, odourless gas that is totally unreactive. It is extracted from natural gas wells, some of which contain gas that is 7% helium. It is used in deep sea diving for balloons and, liquid helium is used for low temperature research (MRI scanners). The Earth’s atmosphere contains 5 parts per million by vol, (400 million tonnes) but it is not worth extracting it from this source at present.
20 Ne 10 Discovered : by Sir William Ramsay + Travers in 1898Origin : The name is derived from the Greek ‘neos’, meaning new.Description :A colourless, odourless gas. 18 parts per million of air. Neon will not react with any other substance. It is produced from liquid air for ornamental lighting (i.e. neon signs) because it glows red when an electrical discharge is passed through it.
18 Ar 40 Discovered : 1899 by Lord Rayleigh and Sir William RamsayOrigin : From the Greek ‘argos’ meaning inactive.Description : The third most abundant gas, making up one percent of the atmosphere. The quantity has increased since the Earth was formed because radioactive potassium turns into argon as it decays. Argon is a colourless, odourless gas that is totally inert to other substances, and for this reason it is ideal in light bulbs.Welding - Argon provides an inert atmosphere in which welded metals will not oxidise
36 Kr 84 Discovered : by Sir William Ramsay Travers in 1898Origin : The name is derived from the Greek ‘kryptos’, meaning hiddenDescription : A colourless, odourless gas that is inert to everything but fluorine gas. The isotope krypton 86 has a line in its atomic spectrum that is now the standard measure of length : 1 metre is defined as exactly 1,650,763.73 wavelengths of this line. Krypton is one of the rarest gases in the Earth’s atmosphere, accounting for only 1 part per million by volume.
54 Xe 131 Discovered : by Sir William Ramsay andTravers in 1898Origin : The name is derived from the Greek ‘xenos’, meaning strange.Description :A colourless, odourless gas that makes up 0.086 parts per million of the atmosphere. About half a tonne a year is produced from liquid air and used for research purposes.Xenon is also used in specialised light sources.
86 Rn 222 Discovered : by F.E. Dorn in 1900.Origin : The name is derived from radium.Description : Radon was first discovered as the gas produced from radium as it decayed. It is colourless and odourless, and is chemically inert, but it is dangerous because it gives off alpha radiation. There is a detectable amount in the atmosphere, and concentrations can build up indoors in certain localities. (From radioactive decay of rocks)