Answer to Question 1
All of human civilization is spread out over Earth's surface and exposed to anything that falls out of the sky. Meteorites, asteroids, and comets bombard Earth, producing impacts that vary from dust settling on rooftops to blasts capable of destroying all life. In this case, the scientific evidence is conclusive and highly unwelcome. Statistically you are quite safe. The chance that a major impact will occur during your lifetime is so small that it is hard to estimate. But the consequences of such an impact are so severe that humanity should be preparing. One way to prepare is to find those NEOs (near Earth objects) that could hit this planet, map their orbits in detail, and identify any that are dangerous.
Answer to Question 2
By the time the Universe was a few minutes old, the protons, neutrons, and electrons in your body had come into existence. Although those particles formed quickly, they were not linked together to form the atoms that are common today. Most of the matter was hydrogen, and about 25 percent of the mass was helium. Very few of the heavier atoms were made in the big bang. Although your body does not contain helium, it does contain many of those ancient hydrogen atoms unchanged since the Universe began. Your body also contains heavier atoms that were formed by processes of nuclear fusion in the cores of stars. The heaviest atoms in your body were formed during supernova explosions.
The Sun is the nearest star to Earth.
Earth’s Magnetic Field
Tides on Earth
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Under ideal conditions, a single cell of the bacterium E. coli would divide every 20 minutes to ...