Interpreting & Interacting with Earth Systems (OCR GCSE Combined Science A (Gateway): Chemistry): Flashcards
Exam code: J250
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What was the main gas in Earth's early atmosphere?
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What was the main gas in Earth's early atmosphere?
The main gas in Earth's early atmosphere was carbon dioxide, along with water vapour. There was little or no oxygen present.
True or False?
Volcanoes were a major source of gases in Earth's early atmosphere.
True.
Volcanic eruptions released large amounts of carbon dioxide, water vapour, nitrogen, methane and ammonia from the Earth's interior, forming the early atmosphere.
How did photosynthesis by early plants and algae change the atmosphere?
Photosynthesis by early plants and algae used up carbon dioxide and released oxygen, gradually increasing atmospheric oxygen levels over billions of years.
When water vapour condensed, large amounts of .......... dissolved in the oceans, reducing its concentration in the atmosphere.
When water vapour condensed, large amounts of carbon dioxide dissolved in the oceans, reducing its concentration in the atmosphere.
Why was there no atmosphere on early Earth?
The surface of early Earth was molten, which prevented any atmosphere from forming. Only after cooling and solidification did volcanic activity begin to release gases that formed an atmosphere.
True or False?
Today's atmosphere is approximately 20% oxygen and 80% nitrogen.
True.
After billions of years of photosynthesis and CO2 absorption, the atmosphere stabilised at around 20% oxygen and 80% nitrogen, reached approximately 200 million years ago.
What process caused carbonate sediments to form on the early ocean floor?
Precipitation caused carbonate sediments to form. When water vapour condensed and CO2 dissolved in the oceans, carbonate substances were precipitated and settled as sediment.
Which planets today have atmospheres thought to be similar to early Earth's atmosphere?
Venus and Mars today have atmospheres consisting mainly of carbon dioxide, which is thought to resemble Earth's early atmospheric composition.
.......... are thought to be responsible for producing about 90% of all atmospheric oxygen.
Marine algae are thought to be responsible for producing about 90% of all atmospheric oxygen.
Define greenhouse gases.
Greenhouse gases are gases in the atmosphere, such as carbon dioxide, methane and water vapour, that absorb and trap infrared radiation re-emitted from Earth's surface, keeping the planet warm.
True or False?
The Sun's radiation reaches Earth as infrared radiation.
False.
The Sun's radiation reaches Earth as shortwave radiation. It is the Earth's surface that re-emits this energy as infrared radiation, which greenhouse gases then absorb.
Name three greenhouse gases found in Earth's atmosphere.
Three greenhouse gases are carbon dioxide, methane and water vapour. These gases absorb and store infrared radiation, trapping heat in the atmosphere.
Increasing levels of ......... and ......... in the atmosphere are causing the enhanced greenhouse effect.
Increasing levels of carbon dioxide and methane in the atmosphere are causing the enhanced greenhouse effect.
Define the enhanced greenhouse effect.
The enhanced greenhouse effect is the increased trapping of heat caused by rising concentrations of greenhouse gases, particularly carbon dioxide and methane, beyond natural levels.
Why does the greenhouse effect keep Earth's surface at a habitable temperature?
Greenhouse gases absorb infrared radiation re-emitted from Earth's surface and re-radiate it in all directions, including back towards the ground. This natural greenhouse effect keeps Earth's mean surface temperature at about 15 °C instead of approximately −18 °C, making it warm enough to support life.
True or False?
Without any greenhouse gases, Earth's mean surface temperature would be around 15°C.
False.
Without any greenhouse gases, Earth's mean surface temperature would be approximately −18 °C, not 15 °C. The natural greenhouse effect raises the temperature to about 15 °C by trapping infrared radiation re-emitted from Earth's surface.
State two sources of methane as a greenhouse gas.
Two sources of methane are the digestive processes of animals and decomposition of vegetation. Bacterial action in swamps and rice paddy fields also produces methane.
Sources of carbon dioxide include combustion of fossil fuels, respiration, thermal decomposition of carbonate rocks and the effect of .......... on carbonates.
Sources of carbon dioxide include combustion of fossil fuels, respiration, thermal decomposition of carbonate rocks and the effect of acids on carbonates.
Define climate change.
Climate change is a long-term shift in worldwide weather patterns and conditions, driven largely by increasing concentrations of greenhouse gases in the atmosphere.
How does deforestation contribute to rising atmospheric CO2 levels?
Deforestation removes trees that would otherwise absorb CO2 during photosynthesis. With fewer plants available, less CO2 is removed from the atmosphere, so its concentration rises.
True or False?
Increasing agricultural activity contributes to higher methane levels in the atmosphere.
True.
Increasing agricultural activity leads to greater methane production, for example through livestock digestion and landfill sites where waste decomposes.
Scientists analyse the percentage of .......... in the atmosphere alongside temperature records to build evidence for climate change.
Scientists analyse the percentage of CO2 in the atmosphere alongside temperature records to build evidence for climate change.
Give two reasons why historical climate data is less reliable than modern measurements.
Historical data is less reliable because accurate instrumentation did not exist and fewer locations were measured. Modern satellites and instruments allow global, precise records to be taken.
What are climate mitigation strategies?
Climate mitigation strategies are actions that help populations adapt to a changing climate, such as investing in flood defences, changing crop types or redesigning buildings to cope with extreme weather.
True or False?
Rising sea levels are a consequence of melting polar ice caps caused by global warming.
True.
Climate change causes polar ice caps to melt, which raises sea levels worldwide. Rising sea levels increase the risk of coastal flooding, threatening low-lying areas and island nations.
Why does a warmer ocean surface lead to more destructive storms?
A warmer ocean surface causes more water to evaporate into the atmosphere. This extra moisture means storms and hurricanes carry more energy and are more destructive.
Analysis of .......... trapped in ancient ice can be used to estimate past atmospheric compositions and climate conditions.
Analysis of gas bubbles trapped in ancient ice can be used to estimate past atmospheric compositions and climate conditions.
How does burning fossil fuels contribute to climate change?
Burning fossil fuels releases CO2 into the atmosphere. As CO2 is a greenhouse gas, higher concentrations trap more heat, raising global temperatures and driving climate change.
What is carbon monoxide and why is it dangerous?
Carbon monoxide is a colourless, odourless toxic gas produced by incomplete combustion. It binds to haemoglobin in the blood, preventing oxygen transport and potentially causing death.
True or False?
Complete combustion of a hydrocarbon produces carbon monoxide and water.
False.
Complete combustion produces carbon dioxide and water. Carbon monoxide is a product of incomplete combustion, which occurs when there is insufficient oxygen.
Why does incomplete combustion occur in some engines and boilers?
Incomplete combustion occurs because there is insufficient oxygen available to burn all the fuel completely. This produces carbon monoxide and soot instead of carbon dioxide.
Sulfur dioxide dissolves in rainwater to form ........., which corrodes metal structures and damages aquatic ecosystems.
Sulfur dioxide dissolves in rainwater to form acid rain, which corrodes metal structures and damages aquatic ecosystems.
State two harmful effects of soot from incomplete combustion.
Soot causes respiratory problems and blackens buildings and statues, accelerating corrosion. It consists of carbon particles that clump together and fall back to the ground.
What is acid rain and what gases cause it?
Acid rain is rain made acidic by dissolved sulfur dioxide and oxides of nitrogen from burning fossil fuels. It damages ecosystems, corrodes structures and contaminates water supplies.
True or False?
Oxides of nitrogen in the atmosphere mainly come from industrial chimneys burning coal.
False.
Oxides of nitrogen come largely from vehicle exhausts. They also contribute to acid rain and photochemical smog.
All fossil fuels contain carbon, hydrogen and small quantities of ........., which leads to ......... being released on combustion.
All fossil fuels contain carbon, hydrogen and small quantities of sulfur, which leads to sulfur dioxide being released on combustion.
Give two products of incomplete combustion of a hydrocarbon fuel.
Two products of incomplete combustion are carbon monoxide and carbon particulates (soot). Unburnt hydrocarbons may also be released.
Define potable water.
Potable water is water that has been processed to make it safe for human consumption and daily use. It may contain small, regulated amounts of dissolved minerals and must be free of harmful bacteria.
True or False?
Potable water is the same as pure water.
False.
Pure water contains only H2O molecules. Potable water may contain dissolved minerals and salts in small regulated quantities — it is safe to drink but not chemically pure.
What is the acceptable pH range for potable water?
Potable water should have a pH between 6.5 and 8.5. This range ensures it is neither too acidic nor too alkaline for safe consumption.
During water treatment, .......... is used to remove debris such as soil and grit, and .......... kills harmful bacteria.
During water treatment, filtration is used to remove debris such as soil and grit, and sterilisation kills harmful bacteria.
What are aquifers?
Aquifers are porous rocks that store water underground. Water collected in aquifers is called groundwater and is one source of fresh water used for drinking.
Why is desalination an expensive method of producing potable water?
Desalination is expensive because it requires large amounts of energy to remove salt from seawater, either by distillation or by forcing water through membranes in reverse osmosis.
True or False?
Chlorine gas can be used to sterilise water during the treatment process.
True.
Chlorine gas is bubbled through water to kill bacteria and microbes. Ultraviolet light and ozone are alternative sterilisation methods.
How does reverse osmosis remove salt from seawater?
In reverse osmosis, seawater is forced through a semi-permeable membrane that only allows water molecules to pass through. Larger salt ions are blocked and left behind.
Water stored in reservoirs, lakes and rivers is called ........., whereas water held in porous rocks underground is called ...........
Water stored in reservoirs, lakes and rivers is called surface water, whereas water held in porous rocks underground is called groundwater.
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