You also contain much smaller amounts of the other elements that are essential for life. While most of the cells in your body regenerate every seven to 15 years, many of the particles that make up those cells have actually existed for millions of millennia. The hydrogen atoms in you were produced in the big bang, and the carbon, nitrogen and oxygen atoms were made in burning stars. The very heavy elements in you were made in exploding stars.
The size of an atom is governed by the average location of its electrons. If the nucleus were the size of a peanut, the atom would be about the size of a baseball stadium. If we lost all the dead space inside our atoms, we would each be able to fit into a particle of lead dust, and the entire human race would fit into the volume of a sugar cube.
As you might guess, these spaced-out particles make up only a tiny portion of your mass. The mass of the quarks, which comes from their interaction with the Higgs field, accounts for just a few percent of the mass of a proton or neutron. Gluons, carriers of the strong nuclear force that holds these quarks together, are completely massless. Your body is a small-scale mine of radioactive particles. You receive an annual millirem dose from the natural radioactivity originating inside of you.
They add about 27 millirem to your yearly dose of radiation. These cosmic particles can sometimes disrupt our genetics, causing subtle mutations, and may be a contributing factor in evolution.
In addition to bombarding us with photons that dictate the way we see the world around us, our sun also releases an onslaught of particles called neutrinos. Neutrinos are constant visitors in your body, zipping through at a rate of nearly trillion every second. Aside from the sun, neutrinos stream out from other sources, including nuclear reactions in other stars and on our own planet.
Many neutrinos have been around since the first few seconds of the early universe, outdating even your own atoms. But these particles are so weakly interacting that they pass right through you, leaving no sign of their visit. You are also likely facing a constant shower of particles of dark matter.
Looking at the density of dark matter throughout the universe, scientists calculate that hundreds of thousands of these particles might be passing through you every second, colliding with your atoms about once a minute. Ali Sundermier writes for Symmetry Magazine, an online magazine about particle physics. The elements are arranged in order of their atomic number, with hydrogen and helium at the top of the table, and the more massive elements below.
The periodic table is a useful device because for each element, it identifies the chemical symbol, the atomic number, and the mass number, while organizing elements according to their likelihood to react with other elements. The number of protons and electrons in an element are equal. The number of protons and neutrons may be equal for some elements, but are not equal for all.
Visit this website to view the periodic table. In the periodic table of the elements, elements in a single group have the same number of electrons that can participate in a chemical reaction. What is the meaning of a mass number shown in parentheses? Although each element has a unique number of protons, it can exist as different isotopes. An isotope is one of the different forms of an element, distinguished from one another by different numbers of neutrons. The standard isotope of carbon is 12 C, commonly called carbon twelve.
All of the isotopes of carbon have the same number of protons; therefore, 13 C has seven neutrons, and 14 C has eight neutrons. The different isotopes of an element can also be indicated with the mass number hyphenated for example, C instead of 12 C. Hydrogen has three common isotopes, shown in Figure 2.
An isotope that contains more than the usual number of neutrons tend to be unstable, and unstable isotopes are radioactive. A radioactive isotope is an isotope whose nucleus readily decays, giving off subatomic particles and electromagnetic energy. Different radioactive isotopes also called radioisotopes differ in their half-life, the time it takes for half of any size sample of an isotope to decay.
For example, the half-life of tritium—a radioisotope of hydrogen—is about 12 years, indicating it takes 12 years for half of the tritium nuclei in a sample to decay. Excessive exposure to radioactive isotopes can damage human cells and even cause cancer and birth defects, but when exposure is controlled, some radioactive isotopes can be useful in medicine. For more information, see the Career Connections. The controlled use of radioisotopes has advanced medical diagnosis and treatment of disease.
Interventional radiologists are physicians who treat disease by using minimally invasive techniques involving radiation. Many conditions that could once only be treated with a lengthy and traumatic operation can now be treated non-surgically, reducing the cost, pain, length of hospital stay, and recovery time for patients.
For example, in the past, the only options for a patient with one or more tumors in the liver were surgery and chemotherapy the administration of drugs to treat cancer. Some liver tumors, however, are difficult to access surgically, and others could require the surgeon to remove too much of the liver. Moreover, chemotherapy is highly toxic to the liver, and certain tumors do not respond well to it anyway.
In some such cases, an interventional radiologist can treat the tumors by disrupting their blood supply, which they need if they are to continue to grow. In the days and weeks following the procedure, the radiation emitted from the seeds destroys the vessels and directly kills the tumor cells in the vicinity of the treatment. Radioisotopes emit subatomic particles that can be detected and tracked by imaging technologies.
One of the most advanced uses of radioisotopes in medicine is the positron emission tomography PET scanner, which detects the activity in the body of a very small injection of radioactive glucose, the simple sugar that cells use for energy. It was possible. But many of Reyniers's animals died and those that survived had to be fed on special food. This is because bacteria in the gut help with digestion. You could exist with no bacteria, but without the help of the enzymes in your gut that bacteria produce, you would need to eat food that is more loaded with nutrients than a typical diet.
Depending on how old you are, it's pretty likely that you have eyelash mites. These tiny creatures live on old skin cells and the natural oil sebum produced by human hair follicles.
They are usually harmless, though they can cause an allergic reaction in a minority of people. Eyelash mites typically grow to a third of a millimetre and are near-transparent, so you are unlikely to see them with the naked eye. Put an eyelash hair or eyebrow hair under the microscope, though, and you may find them, as they spend most of their time right at the base of the hair where it meets the skin. Around half the population have them, a proportion that rises as we get older.
Your eyes are very sensitive, able to detect just a few photons of light. If you take a look on a very clear night at the constellation of Andromeda, a little fuzzy patch of light is just visible with the naked eye.
If you can make out that tiny blob, you are seeing as far as is humanly possible without technology. Andromeda is the nearest large galaxy to our own Milky Way. But "near" is a relative term in intergalactic space — the Andromeda galaxy is 2.
When the photons of light that hit your eye began their journey, there were no human beings. We were yet to evolve. You are seeing an almost inconceivable distance and looking back in time through 2.
Despite what you've probably been told, you have more than five senses. Here's a simple example. Put your hand a few centimetres away from a hot iron. None of your five senses can tell you the iron will burn you.
Yet you can feel that the iron is hot from a distance and won't touch it. This is thanks to an extra sense — the heat sensors in your skin. Similarly we can detect pain or tell if we are upside down. Another quick test. Close your eyes and touch your nose. You aren't using the big five to find it, but instead proprioception. This is the sense that detects where the parts of your body are with respect to each other.
It's a meta-sense, combining your brain's knowledge of what your muscles are doing with a feel for the size and shape of your body. Without using your basic five senses, you can still guide a hand unerringly to touch your nose. Just like a chicken, your life started off with an egg. Not a chunky thing in a shell, but an egg nonetheless. However, there is a significant difference between a human egg and a chicken egg that has a surprising effect on your age. Human eggs are tiny.
They are, after all, just a single cell and are typically around 0.
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