Introduction

Our home, the Earth

The Earth is the third planet away from the Sun.[1] To date, it is the only planet that has been known to support the growth of life-forms. These life-forms include organisms ranging from the smallest bacteria to us, humans. In order to support the growth of various types of organisms, numerous conditions have to be met to allow a favourable environment for organisms to live in. These favourable conditions include the atmospheric condition, the right temperature, the sources of food and water. These basic conditions must be fulfilled in order for life on Earth to sustain and flourish.[2]

The Sun plays an indispensable role in ensuring these basic conditions are met. The greatest source of energy for the Earth is the Sun. [3] By supplying heat and light energy, the Sun supports life on Earth. The heat energy ensures that the Earth is of a suitable temperature, allowing organisms to survive on Earth. Earth would become too cold to support the growth of life-forms without the warming rays of the sun. Additionally, as light energy provided by Sun is a prerequisite for photosynthesis,  [2] plants on earth can carry out photosynthesis. This is instrumental in supporting life on Earth as these plants become the source of food for the rest of the food chain.

Fig 1. The Sun provides light and heat energy to Earth, supporting life.[4]

The Sun and radiation

The heat and light energy emitted by the Sun come from the infrared and visible light regions of the Sun’s electromagnetic radiations.[5]  Furthermore, the energy emitted by the Sun can be in the form of ultraviolet radiations as well.

Ultraviolet radiations exist in 3 types[6], these are UV-A, UV-B as well as UV-C. Firstly, UV-A has the longest wavelength (320-400nm) and hence the lowest energy of the 3 types of UV radiation. Being the one with the lowest energy, it is the least damaging. It is also able to be radiated onto Earth. Secondly, UV-B has an intermediate wavelength (280-320nm) among the 3 types and is absorbed by the ozone found in the stratosphere. The third type of UV radiation is UV-C, which has the shortest wavelength (200-280nm) and the strongest energy of the 3.

The ozone layer

The ozone layer is a layer found in the stratosphere of the Earth’s atmosphere.[7] Consisting of the O3 ozone molecules, the ozone layer is a critical barrier which shields the Earth from the harmful UV radiation.

World without ozone

A common misconception is that the UV type that poses the greatest danger is UV-C because, even has the highest energy of all the three types of ultraviolet radiation. However, this is not the case as UV-C radiation is completely absorbed by both the ozone and the oxygen molecules found in the stratosphere. As a result, UV-C is fully blocked from reaching us, while on the other hand, UV-A and UV-B are able to penetrate the stratosphere, where UV-B only absorbed by ozone and not oxygen.

Prolonged negligence and the increase in damaging human activities can harm the environment in multiple ways. For example, a severe consequence of an increase use of chlorofluorocarbons (CFCs) can potentially damage the ozone layer. Without the ozone to shield the radiations from the organisms living on earth, UV-C can no longer be absorbed by ozone and its radiation has to be solely managed by oxygen molecules present, whereas UV-B will be completely unabsorbed and will be able to radiate onto the Earth’s surface. Similarly, the loss of the protective ozone against UV-C will increase the chances of it being radiated onto Earth, just like UV-B.

Functions of UV radiation

Energies of the Sun, such as the visible light that ‘enables’ us to see, and the infrared radiation trapped that helps maintain an appropriate temperature not too cold for humans to survive in, are examples of positive benefits of the Sun’s radiations. The positive functions[8] of UV radiation can range from triggering the body to produce vitamin D essential for strengthening the immune system, to being used as a source of sterilisation to kill pathogens and microorganisms found on the laundry.

Biological effects of UV radiation

Apart from the positive functions of UV radiation, prolonged exposure to high levels of UV radiation can cause severe biological effects in organisms. For example, some of the negative biological effects[8] of UV radiation can range from melanoma (skin cancer), cataracts resulting from eye damage, to the destruction of the immune system in the human body. Hence, the concept of how exposures to UV radiation can results in these outcomes as well as its implications will be discussed further.

Reference:

1: National Aeronautics and Space Administration. [Internet]. Earth – In Depth. [cited 2017 Mar 15]. Available from: http://solarsystem.nasa.gov/planets/earth/indepth

2: Karmarkar B. [Internet]. 2014. Why is life possible on Earth only? [cited 2017 Mar 15]. Available from: https://www.quora.com/Why-is-life-possible-on-earth-only

3: Jet Propulsion Laboratory. [Internet]. Genesis: Search for Origins. [cited 2017 Mar 15]. Available from: http://genesismission.jpl.nasa.gov/science/mod3_SunlightSolarHeat/

4: WeatherSTEM. [Internet]. 2017. The Sun’s Energy as a Resource: Key Points. [cited 2017 Mar 15]. Available from: https://learn.weatherstem.com/modules/learn/lessons/1/14.html

5: Carnegie Mellon University. [Internet]. 2003. The Sun & its energy. [cited 2017 Mar 15]. Available from: http://environ.andrew.cmu.edu/m3/s2/02sun.shtml

6: Nanyang Technological University. 2017. CM8001 Unit 2 Lecture Notes: Protecting the Ozone Layer. [cited 2017 Feb 23].

7. Weatherquestions. [Internet]. 2012. What is the ozone layer? [cited 2017 Mar 15]. Available from: http://www.weatherquestions.com/What_is_the_ozone_layer.htm

8: Science Learning Hub [Internet]. 2008. Positive and negative effects of UV. [cited 2017 Feb 23]. Available from: https://www.sciencelearn.org.nz/resources/1304-positive-and-negative-effects-of-uv

 

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