This week’s question was asked by Kaylee Salzwedel, Tomah High School senior.
QUESTION: What is the universe made of?
ANSWER: Everything we see and touch, and, yes, the air that we breathe, is made of atoms. Atoms are composed of protons, neutrons and electrons. The protons and neutrons are stuck together into the nucleus, and the nucleus is surrounded by orbiting electrons. It’s the planetary model of the atom, analogous to our eight planets orbiting the sun. A somewhat more accurate model is one that has a dense nucleus core surrounded by a cloud of electrons. The term “element” is used for atoms with a given number of protons.
All the elements, some 118 of them, are composed of various numbers of these building blocks. Hydrogen, the most plentiful element, consists of one proton and one electron. Helium has two protons, two neutrons, and two electrons. Carbon has six protons, six neutrons, and six electrons. The heavier, more massive elements, keep building up the number of protons, neutrons, and electrons. Uranium, one of the most massive elements found in nature, has 92 protons, 92 neutrons, and 92 electrons.
Some new finding turned up about 30 years ago. Only about five percent of the universe is made of atoms. Most of the universe seems to be missing; 24 percent is cold dark matter, and 71 percent is dark energy.
Astrophysicists do not know the whereabouts of this missing matter. Brown dwarfs, black holes, and undiscovered particles are good candidates. Until they find it, it really doesn’t matter (pun intended).
That leaves us to concentrate on the atoms that we encounter in everyday life − atoms we can see and touch, and atoms that excite our sense of smell, taste and hearing. The elements are arranged in a meaningful way on the Periodic Table.
Let’s look at some interesting facts about the elements. Helium is lighter than air, and so it’s perfect for putting in balloons at parties. Hydrogen is an even lighter gas than helium. But hydrogen is explosive, and if a hydrogen balloon got close to the lit candles on a birthday cake, that could be a disastrous party.
Oxygen is necessary for life on Earth, but about one percent of the sun is oxygen. Carbon is found in diamonds, graphite, coal, crude oil and you and me. Carbon-12 (six protons, six neutrons) is the most common form. But Carbon-14 (six protons, eight neutrons) is radioactive and is useful in finding the age of formerly living things.
A small amount of carbon in living things is of the Carbon-14 variety. The amount of Carbon-14 in our environment remains constant as new Carbon-14 is being created in the upper atmosphere by cosmic rays.
Living things ingest materials that contain carbon, so the percentage of Carbon-14 in living things, such plants and animals, remains the same as the percentage of Carbon-14 in the environment. Once an organism dies, the Carbon-14 is no longer replaced. The percentage of Carbon-14 begins to decrease at a constant rate. By measuring the percentage of Carbon-14 in the remains of the plant or animal, scientists can estimate when that organism lived and died.
For example, if the amount of Carbon-14 in a dead plant or animal is half the natural concentrations of Carbon -14, a researcher would estimate the organism died 5,730 years ago, which is the half-life of Carbon-14. If the amount of Carbon-14 remaining is one-fourth the usual concentration, then the plant or animal is twice 5,730 years, or 11,460 years old. Carbon-14 acts as sort of atomic clock.
One of the most amazing Carbon-14 dating projects was the Dead Sea Scrolls that were discovered in 1946 and 1947 by Bedouin shepherds in the Qumran Caves in the Judean Desert along the Dead Sea. The Dead Sea Scrolls were written on animal hides and papyrus, both living materials before being put into use.
The accuracy of Carbon-14 dating was confirmed by the naming of people, dates, and cities that occurred at the time of the writing, which ranged from three centuries BC to one century AD.
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Larry Scheckel is a retired Tomah High School physics teacher.
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