C13: The Earth's atmosphere Flashcards
What are the gasses in the atmosphere today?
78% nitrogen
21% oxygen
Other gasses e.g. co2, water vapour and argon
Why can’t scientists be certain about the early atmosphere?
The Earth is ~4600 million years old.
Describe how the composition of the atmosphere changed
In the early atmosphere, there was high volcanic activity. Volcanoes released gasses that formed the atmosphere, such as water vapour and methane. As the Earth cooled, the water condensed to form the oceans. Huge amounts of CO2 were also released. In this early stage, the atmosphere consisted mainly of CO2 with little oxygen. Some of the CO2 dissolved in the oceans to form a weak acid, which reacted with minerals in the sea to form precipitates, and over time, this formed sediments of carbonate rock on the sea bed. Some of the CO2 in the sea was used to make corals and shells of organisms such as mussels, when they died, they formed the sedimentary rock; limestone (which also removed CO2 from the atmosphere). So the CO2 levels fell.
How did the oxygen content in the atmosphere increase?
2.7 billion years ago, photosynthetic algae first evolved in the oceans. Photosynthesis produced oxygen which entered the atmosphere. Plants evolved over the next billion years and increased the oxygen content in the atmosphere. At some point the level of oxygen reached a point where animals could evolve.
What are fossil fuels?
Formed over millions of years - they are non renewable and will run out
How is coal formed?
From the remains of ferns and trees. If they die in marshy wetlands, then they do not decompose due to lack of oxygen or acidic conditions which both prevent bacteria from carrying out decomposition. Over time, the plant remains are covered with sediment and compressed - high temperature and pressure creates coal.
How is crude oil formed?
Formed from plankton (tiny plants and animals found in the sea). When they die, they settle in the mud on the sea-bed ( if oxygen is not present, they do not decompose). Over time, they’re compressed by sediment and heat and pressure convert them into crude oil.
How is natural gas formed?
Natural gas is mainly the hydrocarbon; methane. It is often found near deposits of oil as it is formed from plankton in a similar way to oil.
How do fossil fuels relate to carbon?
They all contain trapped carbon, which was part of the CO2 taken in by photosynthesis.
Describe the greenhouse effect
Energy from the sun travels as short wave UV radiation/ visible light. Some of the short wave radiation simply reflects back into space, but most passes easily through the atmosphere (because short wavelength radiation doesn’t interact strongly with gas molecules in the atmosphere). The energy of the radiation is absorbed when it reaches the surface of the Earth, and is then radiated as long wavelength radiation e.g. infra-red. Some of this radiation interacts with greenhouse gasses in the atmosphere (energy is absorbed), as the energy is trapped, the temperature of the atmosphere increases.
Why is the greenhouse effect important?
It keeps the Earth warm enough to support life, without it, it would be too cold for most organisms to survive.
How can levels of minor greenhouse gasses be altered?
Water vapour - temperature of the air
CO2 + Methane - human activity
How is CO2 in the atmosphere increasing?
Burning of fossil fuels ( petrol/ diesel for cars, coal for electricity/ gas for heating).
Deforestation/ burning forests
How can CO2 be absorbed?
By growing trees
How can Methane levels be increased?
Growing rice in paddy fields.
Farming cattle which passes wind.
