Question

There has been a steady decrease in the ratio of \({ }^{14} \mathrm{C}\) to \({ }^{12} \mathrm{C}\) in the atmosphere over the past decade. Explain how this is consistent with the view that the well documented increase in atmospheric carbon dioxide concentrations is primarily due to emissions from the combustion of fossil fuels.

Short answer

The decreasing ^{14}C/ ^{12}C ratio aligns with fossil fuel emissions raising ^{12}C, explaining the CO2 rise.

Step-by-step solution

Identify the Source of Fossil Fuels

Fossil fuels are composed of carbon compounds that are millions of years old. During this time, any ^{14}C they initially contained would have decayed (half-life of approximately 5730 years), leaving primarily ^{12}C.

Understand the Impact on Atmospheric Ratio

When fossil fuels are burned, they emit large amounts of ^{12}C into the atmosphere, increasing the overall concentration of this isotope. Fossil fuels contain little to no ^{14}C due to its longer decay period, so emissions from these sources do not replenish atmospheric ^{14}C.

Analyze the Decrease in ^{14}C Ratio

As more fossil fuels are burned, the additional ^{12}C dilutes the concentration of ^{14}C in the atmosphere, leading to a decreased ratio of ^{14}C to ^{12}C.

Correlate with Increasing CO2

The steady increase in atmospheric CO2 is consistent with increased fossil fuel use, as these fuels release carbon dioxide when combusted. This explains both the rising levels of CO2 and the changing ratio of carbon isotopes.

Key concepts

Fossil Fuels

Fossil fuels like coal, oil, and natural gas are natural energy sources that have been formed over millions of years. They originate from the remains of ancient plants and animals that have been buried under layers of sediment and rock. Due to the immense pressure and heat over a long period, these organic materials have transformed into rich carbon-based resources.
Fossil fuels are extracted and used for different forms of energy, such as electricity, transportation, and heating. However, they are primarily made up of carbon, mostly in the form of ^{12}C, due to the decay of radioactive isotopes over such a long period without replenishment. When burned, they release this carbon back into the atmosphere, significantly impacting the carbon isotope ratio in our environment.

Carbon Dioxide Emissions

Carbon dioxide (CO2) is a naturally occurring gas that is introduced into the atmosphere through a variety of processes, including respiration and volcanic eruptions. However, human activities such as burning fossil fuels substantially contribute to CO2 emissions.
When fossil fuels are combusted, the carbon stored within them reacts with oxygen to form carbon dioxide. The increasing release of ^{12}C from fossil fuels enhances atmospheric CO2 levels.
This steady increase in emissions affects global climate patterns and contributes to climate change by trapping heat in the earth's atmosphere, a phenomenon known as the greenhouse effect.

Radioactive Carbon Dating

Radioactive carbon dating, also known as radiocarbon dating, is a method used to determine the age of an object containing organic material. It is based on the presence of ^{14}C, a radioactive isotope of carbon that is formed in the upper atmosphere through the interaction of cosmic rays with nitrogen-14.
While living organisms constantly exchange carbon with their environment, maintaining a consistent ratio of ^{14}C to ^{12}C, this exchange stops upon their death. The ^{14}C then begins to decay at a known rate (half-life of approximately 5730 years).
This technique allows scientists to date ancient biological samples by comparing their remaining ^{14}C to the expected levels at the time of death, giving us vital insights into past climates and ecosystems.

Atmospheric Chemistry

Atmospheric chemistry involves the study of chemical processes that take place in the Earth's atmosphere. It focuses on understanding how different gases and particles interact, how they are transformed, and how they affect both climate and air quality.
Key factors in atmospheric chemistry include concentrations of carbon dioxide and other greenhouse gases, which influence temperature and weather patterns. Understanding changes in the carbon isotope ratios, particularly the decline in ^{14}C relative to ^{12}C, is crucial in this field.

• This decline is a direct consequence of burning fossil fuels, which adds more ^{12}C to the atmosphere.
• These changes have wide-ranging effects on everything from global warming to the acidification of oceans.

Through comprehensive studies, atmospheric chemists help develop strategies to mitigate human impacts on the environment and improve public health.