(Figure 3) We breathe in and out through our noses all day long. Our noses adapt the air that enters it to the lungs in the finest way and direct part of that air to the olfactory region, and thus we perceive smells at the same time.
You breathe an average of 23,040 times each day. During this constantly repeated process, your nose adapts air for the lungs in the most appropriate manner. In doing so, it performs another very important task: It detects and monitors odors. (Figure 3)
(Figure 4) The figure shows the olfactory region to which is directed part of the air we inhale.
The total population of a sniff is a billion trillion molecules, nearly all of them normally in the mix we call air. The scent particles, far too small to be seen with the naked eye, are contained within this enormous quantity of molecules. After you have breathed in, special turbinate bones in the nose direct a portion of that air to the scent-perceiving region. In this way, scent molecules arrive at a region in the upper part of the nasal cavity, some 7 centimeters (2.756 inches) inside and above the nostrils. (Figure 4) When you lift a flower to your nose and smell its perfume, a great number of molecules reach the scent-perception region.
Most people are unaware that they possess such an extraordinary chemical-analysis facility that lies within the scent-perception region, works non-stop to analyze odors in the surrounding area. As you go about your daily life, making no special effort to perceive smells, this facility is in action nonetheless. Even when you sleep at night, it perceives potentially harmful smells such as smoke and warns you. This facility is so utterly perfect that it is able to determine more than 10,000 different odors , functioning with a perfect accuracy and sensitivity.
The small scent molecules that form the basis of aromas come in different shapes and sizes. The breathtaking scents in a garden, the attractive aromas of a delicious meal, or the repellent stench of rotting fruit all arise from different molecules. The chemical plant in your nose is easily able to identify all these different molecules, and can even immediately distinguish molecules with the same atomic formulae. For example, the minute difference between the molecules L-carvone and D-carvone stems from their atoms having different sequences. Despite this exceedingly close similarity, a human nose can easily distinguish between the two, telling us that the former suggests cumin and the latter, spearmint.
Another property of the nose that amazes scientists is its immaculate sensitivity. The minimum concentration of a substance required for us to recognize its particular smell is known as the smell threshold. The analysis mechanism in our noses in unbelievably sensitive; some scents in the air can be perceived at concentrations of less than one part in a trillion! Research has shown, for example, that the threshold for perception of butyric acid is a 10 billion fold dilution of the pure substance.
The more molecules are investigated, the more marvels of the scent perception system are revealed. What we perceive as any single aroma is actually an effect caused by large numbers of different molecules. For instance, the "ordinary" smell of white bread actually consists of around 70 different scent molecules. It is estimated that the smell of coffee results from a combination of at least 150 different chemical substances. A top-quality perfume may contain 500 ingredients. The analysis mechanism in your nose identifies these chemical substances at very low concentrations, without your being aware of it. All these processes that take place between your detecting a smell and concluding that it belongs to coffee brewing, take place in much less than a second. Bearing all this in mind, the superior creation in the scent perception mechanism can doubtless be better appreciated.
God reveals in one verse that:
And in your creation and all the creatures He has spread about there are Signs for people with certainty. (Surat al-Jathiyya: 4)