today's video is all about the earth's atmosphere and how it evolved to be what it is today with a composition of about eighty percent nitrogen 20 oxygen and all the other gases like carbon dioxide water vapor and the noble gases making up less than one percent to do this we'll take a look at the role that volcanic activity played to create the early carbon dioxide rich atmosphere and how algae and plants then reduced that abundance of co2 and increased the amount of oxygen in the atmosphere first though we need to say that this is only a theory although it's supported by lots of evidence the fact that has taken place over the past 4.6 billion years means that there's not as much as we might like so we still consider it a theory in the first billion years of earth's history the earth was really dry and there was intense volcanic activity which produced loads of carbon dioxide water vapor and nitrogen along with smaller amounts of methane and ammonia this meant that the early atmosphere was mostly carbon dioxide much like the atmospheres of mars and venus today as the water vapor condensed into liquid water though it formed the oceans and this allowed lots of the carbon dioxide from the atmosphere to dissolve in them where it could go on to form carbon precipitates and then finally become sediments in the seabed the next major change started about 2.7 billion years ago slowly at first as algae began to appear but becoming more rapid has green plants evolved over the following billion years this is because both of these groups of organisms are able to photosynthesize and as you can see from this equation for photosynthesis this not only takes in carbon dioxide but also produces oxygen so as algae implants have photosynthesized over the past couple of billion years the amount of carbon dioxide in the atmosphere has slowly declined while oxygen levels have slowly built up which eventually allowed more complex life like animals to evolve now algae and green plants could only hold a relatively small amount of carbon in their bodies when they died though they fell to the seabed and became buried in layers of sediment and over millions of years this sediment became compressed to form sedimentary rock oil and gas which trapped the carbon to stop it from getting back into the atmosphere the exact substance that was formed in this process though depends on the type of organism being buried and the conditions involved for example crude oil and natural gas are formed mainly from dead plankton which are a diverse group of tiny organisms that float in the ocean on the other hand coal is a type of sedimentary rock made from thick deposits of dead plant material meanwhile limestone is also a sedimentary rock but is mostly made of the calcium carbonate that marine organisms incorporate into their shells and skeletons so to quickly recap all of this for the first billion years there was loads of volcanic activity which produced lots of carbon dioxide and a few other gases then as the water vapor in the atmosphere condensed it formed the oceans which the carbon dioxide was then able to dissolve in then a couple of billion years later algae and green plants evolved and because of all the photosynthesis that they did they decreased atmospheric carbon dioxide levels and increased oxygen levels so overall we now have an atmosphere made mostly of oxygen and nitrogen and because lots of plants algae and other organisms died and sunk to the bottom of the oceans we have large quantities of sedimentary rock and fossil fuels in the ground that's everything for today though so hope you enjoyed it and we'll see you next time