Earth’s atmosphere—wonderfully designed for life
Have you ever wondered about the amazing features of Earth’s atmosphere? It permits light to pass through to us and illuminates the beauty of creation, while providing oxygenated air to breathe, and plant fertilizer in the form of carbon dioxide. It also creates a warming greenhouse effect, and acts as a shield which greatly diminishes the amount of the sun’s harmful ultraviolet rays that can reach us. In short, it is wonderfully designed for life.
Colours of the sky and rainbow
On a cloudless day, the clear sky is a lovely shade of blue, but sometimes it turns red, orange, or pink at dawn, and at dusk (see ‘Colours of the Sky’). And if you look closely as the sun sets over a clear ocean you may even see a green flash before the disk completely disappears. Even the clouds’ appearance can range from brilliant white through to dark grey, depending on the reflection and scattering of light.
Through refraction, reflection, and dispersion, raindrops may separate the light into the seven colours of the rainbow (although in reality there is a full spectrum of light). As well as a primary rainbow, a secondary bow can sometimes be seen higher in the sky, one that is reversed because of a double reflection of light in the rain drops.1 A dark band may also form between the two bows, called the Alexander band (named after Alexander of Aphrodisias who first described it around AD 200), where all reflected light is directed away from the observer (see ‘The Double Rainbow’).
Other optical phenomena in the atmosphere include a halo that sometimes forms around the sun, due to hexagonal ice crystals in thin cirrus clouds. (Sunlight, or moon light, is deflected towards the observer by the ice crystals, forming a ring around the sun (figure 1).)
It is easy to take for granted the awesome wonder and beauty we see in Earth’s atmosphere, but it is only through a narrow range in the electromagnetic spectrum that the light we see gets to us through the atmosphere. The sun produces its strongest electromagnetic radiation in the ultra-violet (UV) and visible light portion of the spectrum. In addition, the atmosphere lets most of the visible light (400–750 nm) through. This allows our world to be illuminated, but it filters out the higher frequency UV radiation that is just outside the visible spectrum. The radiation filtered out includes all the extremely harmful UV-C (100–280 nm) and most of the UV-B light (280–315 nm), excessive exposure to which causes sunburn and skin cancer (figure 2).
The penetration of UV light is restricted by a layer of ozone high in the atmosphere. It lies within the stratosphere, an area of sky that starts from about 10 km (6 mi) above the ground, extending upwards about another 40 km (25 mi). The ozone layer itself starts at about 15 km in altitude to about 30 km.2,3 Chemical reactions involving ozone prevent the energetic UV rays from reaching deeper into the layer just below, the troposphere (Earth’s lowest atmospheric layer), and to the ground. However, much of the less energetic UV-A light (315–400 nm) is permitted to reach the ground, where it aids photosynthesis and plant growth.4 Much higher up, between 60 and 200 km above the Earth, is the ionosphere, which filters out the powerful x-rays that come from the sun, particularly from solar flares, and also from deep space.
The magnetosphere5 also protects the earth from very high energy particles (mainly electrons and protons) that come from the sun, and cosmic rays. These particles are captured by the magnetic field, and bounced back and forth between the polar regions, becoming visible as the awesome aurora light display in the polar regions (aurora borealis—figure 3—in the north, aurora australis in the south).
The Double Rainbow
In the brighter rainbow, light is reflected once by the rain drops. In the higher, fainter bow light is reflected twice by the rain drops. In the darker Alexander band (see photo) light is deflected away from the observer.
Just enough UV-B light makes it through the layered atmosphere to enable us to generate vitamin D in our skin. Although we can get this important vitamin through eating such foods as oily fish, or cod liver oil supplements, it largely comes through the action of sunlight on our skin.6 It is essential for the health of our bones and the immune system, but the winter sun is often too weak at high latitudes. Nevertheless, long exposure to UV-A and UV-B can damage the skin and lead to skin cancer, so too much basking in the sun or under artificial sunbeds is not advisable.7
Our greatest natural protection from UV light is the body’s own sunscreen, a polymer called melanin, which we have in differing amounts.8 Melanin gives human skin its various shades. People who live at low latitudes (nearer the equator) tend to have more melanin, hence darker skin, as they need more protection from the sun’s rays. Those who live at high latitudes, where there is less sunlight, still need to produce enough vitamin D to keep bones and the immune system healthy—so northern Europeans historically have had less melanin and lighter shades of skin.
The greenhouse effect and plant fertilizer
Colours of the Sky
Why is the sky blue? Gases and particles in the air that are smaller than the wavelength of light cause light to be scattered (called Rayleigh scattering). The shorter wavelength of blue light is scattered more than longer wavelengths of light, thus more blue light reaches the observer.
Why are sunsets red? At sunset and sun-rise, the light has to pass through a lot more atmosphere, and so practically all the blue light is scattered away from the observer, thus leaving more yellow and red light to reach the eye.
As well as being warmed by the sun, the earth emits radiation in the infrared (IR) spectrum back into space. However, much of this IR is absorbed in the atmosphere before it can escape. The atmosphere is more opaque at IR wavelengths than those of visible light. Trace gases such as water vapour (H2O) and carbon dioxide (CO2) produce nearly all this trapping effect, helping warm the planet and making it habitable for life. Without greenhouse gases Earth’s temperature would be a whopping 33° C (59.4° F) colder than its current average of about 15° C (59° F)!9 And water vapour causes about 90% of this warming effect.
Carbon dioxide in the air often gets a bad press as the chief culprit for climate change. But it is vital for providing food for plants through the process of photosynthesis. Indeed, plant productivity has surged with the increased CO2 levels in the atmosphere. Plants use the energy of sunlight to convert water and carbon dioxide into sugars and other carbohydrates, and oxygen is also liberated as a by-product.
In turn, humans and animals consume the plants as food, and rely upon the oxygen for respiration, producing water and carbon dioxide as by-products; the reverse process. This apparently simple cyclical process is all part of the wonderful design of life—a testament to the amazing wisdom of God. However, when the details are looked at, the level of complexity is anything but simple.
How awesome is the world in which we live! The atmosphere is remarkably designed for sustaining the life of plants and animals, and us as human beings with protection from harmful radiation. We also live in a world adorned with beauty, including being able to see the stars at night. This is all done through God’s amazing design. This points to the wonder of a wonderfully designed atmosphere, one that is essential for life.
In the words of Psalm 19:1, “The heavens declare the glory of God, and the sky above proclaims his handiwork”, or the well-known hymn of praise:
O Lord my God, When I in awesome wonder,
Consider all the works thy hand hath made,
I see the stars, I hear the mighty thunder,
Thy pow’r throughout the universe displayed.10
References and notes
- Explained in more detail: Sibley, A., Reclaiming the rainbow: the misappropriation of a religious symbol, creation.com/reclaiming-rainbow, 3 Nov 2022. Return to text.
- Ozone molecules are composed of three oxygen atoms. Ozone is a trace gas, making up just 0.00006% of the amosphere; see Ozone layer, education.nationalgeographic.org; acc. 21 Oct 2022. Return to text.
- US Environmental Protection Agency, Basic ozone layer science, epa.gov, acc. 23 Nov 2022. Return to text.
- Anon., Do your plants need UV light?, growace.com, acc. 5 Dec 2022. Return to text.
- Corrado J., The magnetosphere: an invisible force that makes life on earth possible, Creation 44(2):46–48, 2022; creation.com/magnetosphere-life-possible. Return to text.
- Specifically, this occurs through a photochemical reaction with a protein called 7-dehydrocholesterol (7-DHC), which forms vitamin D3 (cholecalciferol). Return to text.
- McNeill, A.M. & Wesner, E., Sun protection and Vitamin D, skincancer.org, 14 May 2018. Return to text.
- People with albinism (albinos), caused by a mutation, either have no melanin, or a greatly reduced amount, associated with pale skin, light blonde hair, and often poor eyesight. Return to text.
- NASA, What is the greenhouse effect? — Climate change: vital signs of the planet, climate.nasa.gov; accessed 21 Oct 2022. Return to text.
- Carl Gustaf Boberg (1856–1940) tr. from the Russian by Stuart Wesley Keene Hine (1899–1989) © 1953 Stuart K Hine Trust/Kingsway’s Thankyou Music. Return to text.