11.1 history of our atmosphere
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atmosphere def
the relatively thin layer of gas that surrounds planet Earth
when was the Earth formed
4.6 billion years ago
what was the Earth like for the first billion years
• it was very hot and turbulent • the earth’s surface was covered with volcanoes belching fire and gases into the atmosphere
how do scientists reconstruct what the Earth’s early atmosphere was like
• gas bubbles trapped in ancient rocks • data gathered from the atmosphere of other planets and moons in the solar system
what is one theory for how the earth’s atmosphere was formed (volcanoes)
• volcanoes released carbon dioxide, water vapour and nitrogen • these gases formed the early atmosphere • water vapour in the atmosphere condensed as the earth gradually cooled down, and fell as rain • water collected in the hollows in the crust as the rock solidified and the first oceans were formed
what is another theory (comets)
• comets could have brought water to earth • as icy comets rained down on the surface of the earth, they melted, adding to its water supplies
what was the early atmosphere made up of
• as the earth began to stabilise, the atmosphere was mainly co2 • there could have been some water vapour and traces of methane and ammonia • little or no oxygen at the time
what does the earth’s early atmosphere resemble
• atmospheres on planets Mars and Venus • our nearest neighbours have atmospheres made up mainly of co2 with little or no oxygen
how has life formed on earth
• life began 3.4 billion years ago when the first simple organisms such as bacteria appeared • 2.7 billion years ago bacteria and other simple organisms such as algae evolved • as plants evolved, they colonised most of the earth so the atmosphere became richer in oxygen • this made it possible for the first animal forms to evolve
what happened when the first simple organisms appeared
they could use the breakdown of chemicals as a source of energy
what happened when bacteria and other simple organisms evolved
• algae could use the energy from the sun to make their own food via photosynthesis • this produced oxygen as a waste product • over the next billion years, the levels of oxygen rose steadily as algae and bacteria thrived in seas • more and more plants evolved (removing co2 and making o2)
what happened after the atmosphere became richer in oxygen
• this made it possible for the first animal forms to evolve • they could not make their own food, relied on algae and plants for their food and on oxygen to respire • earliest living microorganisms could not tolerate a high oxygen concentration because they have evolved without it • they largely died out, there were fewer places where they could survive