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Sharpen Your General Knowledge
Shamim Ansary:
What Is the Electromagnetic Spectrum?
The electromagnetic spectrum is the wide range of electromagnetic (EM) waves from low to high frequency.
The spectrum ranges from low-frequency radio waves, all the way to gamma rays, which have a very high frequency. In the middle of the spectrum is a small region containing the frequencies of light.
Shamim Ansary:
What Is Light Made of, Where Does Light Come From, and Why Is Light a Type of Electromagnetic Radiation?
Light is a familiar everyday phenomena that we take for granted.
When the Sun or other stars shine, we see light. When we turn on a lamp, we see light.
Technically, light is an energy disturbance in the air. Oscillating electric and magnetic fields radiate energy in waves.
The wavelengths and frequency fall in the middle of the electromagnetic spectrum, between ultraviolet and infrared rays. It so happens that our eyes detect radiation at those wavelengths and frequencies in the form of light.
Different elements, and the combinations of elements that make up molecules, emit radiation in different ranges of the electromagnetic spectrum.
Nitrogen-based ammonia, for example, tends to emit microwaves. We cannot see ammonia in space with an optical telescope, but it can be found using a special microwave telescope.
Neon radiation, however, is detected as light. Think of all the neon signs in all the store and restaurant windows you’ve seen.
Technology now allows astronomers to study radiation across the whole electromagnetic spectrum.
Research into all the different kinds of radiation provides far more information, and raises many more questions, about the universe than studying light alone.
Shamim Ansary:
How Dangerous Is Radiation and Are All Types of Radiation Dangerous or Hazardous to Our Health?
There are several types of electromagnetic radiation such as, radio waves, infrared light, visible light, ultraviolet light, and X-rays.
Some radiation from elements can be deadly.
The bombs that the United States dropped on Hiroshima and Nagasaki, Japan, at the end of World War H, were hydrogen and plutonium bombs, respectively.
The radiation from other elements is harmless.
Seventy-eight percent of the air we breathe is nitrogen, whose radiation obviously is not dangerous.
Most types of radiation are harmless at low levels of exposure, but even infrared radiation can be harmful if it is of a high intensity.
Shamim Ansary:
When Did Humans Appear On Earth?
This is not an easy question to answer. Debates rage over which fossils can be called truly hominoid (humanlike), or hominid (human).
The development of human characteristics took place over millions of years. The earliest primate (an order of mammals that includes humans, apes, and monkeys), no bigger than a rat, appeared 60 million years ago.
About 10 million years ago, the Ramapithecus showed remarkable hominoid attributes. But there is no further evidence until 6 million years later.
The first generally accepted hominoid is called Australopithecus, and some believe they are actually the most primitive of the human lineage.
Homo habilis, dating back at least 2 million years in modern-day Africa, is undisputedly human. Less than a half-million years later, Homo erectus lived in Africa as well as in Asia and Europe.
A fossil skull fragment discovered in England is the oldest known example of modern-day humans: a 300,000-year-old Homo sapien.
Shamim Ansary:
Why Is Africa Called the “Birthplace of the Human Race†And When Was Cattle Domesticated In Africa?
Africa is called the birthplace of the human race because scientists have found fossilized bones of human ancestors in eastern and southern Africa that are the oldest of any in the world.
They believe that humans gradually moved out of Africa to populate the rest of the world.
The earliest Homo sapiens, or modern human, found in Ethiopia can be dated back to about 200,000 years ago.
Most scientists believe that the human species originated from the African continent.
Fossil remains of several species of early apelike humans believed to have evolved into modern man, such as Australopithecus afarensis from about 3 million years B.C. have been discovered.
It is believed that cattle was domesticated in North Africa by about 6000 B.C., before agriculture had become widespread.
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