chem-9 Flashcards
Where did the atmosphere come from?
One theory suggests that the early atmosphere came from intense volcanic activity, which released gases that made the early atmosphere very similar to the atmospheres of Mars and Venus today. These atmospheres have:
a large amount of carbon dioxide
little or no oxygen
small amounts of other gases, such as ammonia and methane
Volcanic activity also released water vapour, which condensed as the Earth cooled to form the oceans. Nitrogen was probably also released by volcanoes which gradually built up in the atmosphere because it is unreactive.
what is the modern atmosphere like?
For approximately 200 million years, the proportions of different gases in the atmosphere have been relatively stable.
-nitrogen 80% approx
-oxygen 20% approx
-carbon dioxide, water vapour and noble gases
How has oxygen increased
Plants make their own food by photosynthesis. In this process, carbon dioxide is reacted with water to produce glucose, with oxygen as a by-product:
carbon dioxide + water → glucose + oxygen
6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)
Scientists think that algae first evolved approximately 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere. Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere. Eventually, the amount of oxygen present in the atmosphere enabled animals to evolve.
Explain how carbon dioxide has decreased (sedimentary rocks)
Carbon dioxide is a very soluble gas. It dissolves readily in water. As the oceans formed, carbon dioxide dissolved to form soluble carbonate compounds so its amount in the atmosphere decreased. Carbonate compounds were then precipitated as sedimentary rocks, eg limestone.
Explain how carbon dioxide has decreased (uptake by living organisms and creation of fossil fuels)
Carbon dioxide was also absorbed from the oceans into photosynthetic algae and plants. Many of these organisms, and the simple organisms in the food chains that they supported were turned into fossil fuels, eg crude oil, coal and natural gas, which all contain carbon.
Coal is a fossil fuel which was formed from trees which were in dense forests in low-lying wetland areas. Flooding caused the wood from these forests to be buried in a way that prevented oxidation taking place. Compression and heating over millions of years turned the wood into coal.
Crude oil and natural gas were formed from simple plants and tiny animals which were living in oceans and lakes. These small organisms died and their remains sank to the bottom where they were buried under sediments. The lack of oxygen prevented oxidation from occurring.
Over millions of years, heat and pressure turned the remains of the organisms into crude oil and natural gas. Natural gas contains the smallest molecules and is often found on top of crude oil, trapped under sedimentary rock.
Describe two reasons why the amount of carbon dioxide in the atmosphere decreased over time. (simple form)
Carbon dioxide dissolved in the oceans, and primitive plants used it for photosynthesis.
What is the greenhouse effect
Without greenhouse gases in its atmosphere, the Earth would be about 18°C colder on average than it is now. That would make it too cold to support life as we know it.
Greenhouse gases present in the atmosphere include:
water vapour
carbon dioxide
methane
These greenhouse gases:
Absorb heat radiated from the Earth
then release energy in all directions, which keeps the Earth warm
How does the greenhouse effect work
electromagnetic radiation at most wavelengths passes through the Earth’s atmosphere
the Earth absorbs most of the radiation and warms up
the Earth radiates energy as infrared radiation
some of the infrared radiation goes into space
some of the infrared radiation is absorbed by greenhouse gases in the atmosphere
the lower atmosphere warms up
How are humans increasing the amount of greenhouse gases
farming cattle releases methane
farming rice in paddy fields releases methane
burning fossil fuels in vehicles and power stations releases carbon dioxide
deforestation releases carbon dioxide and reduces the absorption of carbon dioxide through photosynthesis
Are humans causing global warming?
Not everyone in the world agrees that humans are causing global warming by causing the release of greenhouse gases into the atmosphere. Some people believe that the current and ongoing rise in global temperatures is being caused by natural factors and cycles of climate change.
However, the vast majority of scientists do believe that humans are responsible for the increase in greenhouse gases and therefore global warming. This is because the majority of evidence in peer-reviewedjournals supports the theory that human activities are causing an increase in greenhouse gases and this is causing global warming.
However, climate science is complicated and it is difficult to predict and explain what will happen to global temperatures in the future, so scientists cannot be certain about global warming.
The media (eg websites, TV news, newspapers) may sometimes present opinions and articles which are simplified, inaccurate, based on only some of the evidence or biased. It is important for new evidence to be shared with as many people as possible, so that other scientists can check the results and interpretation, and repeat the experiments for themselves.
When evaluating the quality of evidence on an issue like global warming, you should consider:
who did the research and whether they are trustworthy, skilled and experienced
who funded the research, because that might cause some bias
what methods were used to collect and analyse the data, because that might cause uncertainties in the evidence base
which organisation is reporting or publishing the evidence
How is climate different from weather
Climate is different from weather because climate refers to the average temperature and cycles of weather over long periods of time - decades at least. You might talk about the weather being windy last week, or hotter last year than the year before. But unless you compare data for many years you cannot make a judgment about whether the climate is changing.
What has the earth temp been like since it was formed
The Earth’s climate has been constantly changing since the Earth was formed 4.6 billion years ago. This includes several ice ages and periods of much warmer global temperatures. Until 200 years ago, these changes were all caused by natural changes such as volcanic eruptions and changes in the energy that reaches the Earth from the Sun.
What is global warming
Global warming is not the same as climate change. Global warming is usually used to describe the warming of the climate in the past 200 years, which the vast majority of scientists are almost certain has been caused by human activities.
What is one piece of evidence humans have caused global warming
One of the commonly used pieces of evidence that humans are causing global warming is that there is a strong correlation between the increase in global carbon dioxide levels caused by human activities and the increase in global temperatures over the same timescale.
What are the effects of global warming
The effects of global warming include:
glaciers and polar ice melting
sea levels rising
patterns of rainfall changing, producing floods or droughts
habitats changing
