Earth is more active, in terms of both geology and weather, which makes it hard for craters to remain. Even those craters scientists can see on the surface—which may be millions of years old—have been overgrown by vegetation, weathered by wind and rain, and changed by earthquakes and landslides. The Moon, meanwhile, is geologically quiet and has almost no weather, so its hundreds of thousands of craters are easy to see.
The craters are the result of both meteorites and volcanic activity. Interestingly, some of the oldest Earth rocks might be awaiting discovery on the Moon, having been blasted there billions of years ago by asteroid impacts that shook both worlds.
Our muscles, which make up about half of our body mass, control the way the body moves. Muscles work together all the time, whether we are actively playing sports, or quietly reading and writing. Muscles lie in bands just beneath the surface of the skin. A muscle is made up of thousands of fibers bundled together within a protective sheath that consists of blood vessels and nerves. These nerves can be up to 12 inches (30 centimeters) long. A muscle becomes stronger when you work it, which is why people Who regularly exercise have more defined muscle tone than those Who do not exercise. There are about 660 muscles in the human body. The three types of muscle tissue are skeletal, cardiac, and smooth. The main and most unique characteristic of muscle tissue is its ability to contract, or shorten, making some type of movement possible.
Skeletal muscles hold the bones together, and are often called “voluntary” muscles because the brain controls them. The cardiac muscle, which is found only in the heart, contracts to send blood from the heart into the arteries. The brain sends signals to the cardiac muscle to speed up or slow down its contractions, called the heartbeat. Smooth muscles, located in the internal organs such as the stomach and intestines, help these organs or tissues do their job, such as help you digest and eliminate your food.
The deepest hole ever made by humans is in Kola Peninsula in Russia, where in 1989 geologists dug a hole 7.6 miles (12.2 kilometers) deep. The Kola Superdeep Borehole began in the 1970s.
Russian teams used special drilling techniques to dig into the Baltic continental crust, presumed to be about 22 miles (35 kilometers) thick, exposing rocks 2.7 billion years old at the bottom.
Cotton, which comes from flowering Gossypium plants, is a key vegetable fiber used for making clothes, and oil from its seeds can be used in cooking or for making soap. The cotton plant grows in 17 states that make up the U.S. “Cotton Belt”: California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Missouri, Mississippi, Alabama, Louisiana, Florida, Tennessee, North Carolina, South Carolina, Virginia, Georgia, and Kansas. In the United States, where cotton is no longer picked by hand, machines called pickers or strippers harvest the crops.
Cotton-picking machines have spindles that pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers— a series of circular rubber pads—then remove the seed cotton from the spindles and knock the seed cotton into a conveying system. Conventional cotton stripping machines use rollers equipped with alternating bats and brushes to knock the fluffy white bolls, which contain seeds and hairs, from the plants into a conveyor. After harvest, most of the cotton is pressed into large blocks for storage. These cotton bundles are then transported to the cotton gin, a machine that pulls out the seeds from the cotton bolls.
Yes. Mars, the fourth planet from the Sun, is called the Red Planet. It looks red because the rocks on the surface contain rusted iron. It has an atmosphere with clouds, winds, and dust storms—its red dust floats in the atmosphere and gives the planet a red sky.
Mars, which has two moons, orbits the Sun every 687 days and rotates on its axis once every 24 hours and 37 minutes.
1. We should never put anything in or near our eyes, unless we have a reason to use eye drops. We would only do that if our doctor or parent told us to use them.
2. If the lens in our eye doesn’t work quite right, we can get glasses to help us see. Glasses have lenses in them that work with our eye’s own lens to help us see better.
3. Just behind the pupil is a lens. It is round and flat. It is thicker toward the middle.
4. Over the front of our eye is a clear covering called the “conjunctiva.”
5. Blinking helps to wash tears over our eyeballs. That keeps them clean and moist. Also, if something is about to hit our eye, we will blink automatically.
6. Some people start to sneeze if they are exposed to sunlight or have a light shined into their eye.
7. The highest recorded speed of a sneeze is 165 km per hour.
8. Our eyes have many parts. The black part on the front of our eye is called the “pupil.” It is really a little hole that opens into the back part of our eyes.
9. Our body has some natural protection for our eyes. Our eyelashes help to keep dirt out of our eyes. Our eyebrows are made to keep sweat from running into our eyes.
10. The most common injury caused by cosmetics is to the eye by a mascara wand.
11. It is impossible to sneeze with your eyes open.
12. Around the pupil is a colored muscle called the “iris.” Our eyes may be BLUE, BROWN, GREEN, GRAY OR BLACK, because that is the color of the iris.
13. Our eyes are very important to us, and we must protect them. We don’t want dirt, sand, splinters or even fingers to get in our eyes.
14. The reason why your nose gets runny when you are crying is because the tears from the eyes drain into the nose.
15. The space between your eyebrows is called the Glabella.
16. The white part of our eye is called the “sclera.” At the front, the sclera becomes clear and is called the “cornea.”
17. We don’t want our eyes to get scratched or poked. That could damage our sight!
18. Babies’ eyes do not produce tears until the baby is approximately six to eight weeks old.
19. Inside our eye, at the back, is a part called the “retina.” On the retina are cells called “rods” and “cones.” These rods and cones help us to see colors and light.
20. Your eyes blinks over 10,000,000 times a year!
21. The study of the iris of the eye is called iridology.
22. The shark cornea has been used in eye surgery, since its cornea is similar to a human cornea.
23. The number one cause of blindness in adults in the United States is diabetes.
24. The eyeball of a human weighs approximately 28 grams.
25. The eye of a human can distinguish 500 shades of the gray.
26. The cornea is the only living tissue in the human body that does not contain any blood vessels.
27. The conjunctiva is a membrane that covers the human eye.
28. Sailors once thought that wearing a gold earring would improve their eyesight.
29. Research has indicated that a tie that is on too tight cam increase the risk of glaucoma in men.
30. People generally read 25% slower from a computer screen compared to paper.
31. Men are able to read fine print better than women can.
32. In the United States, approximately 25,000 eye injuries occur that result in the person becoming totally blind.
33. All babies are colour blind when they are born.
34. A human eyeball weighs an ounce.
Farmers and state governments use chemical pesticides to protect their crops from insect pests, weeds, and fungal diseases while they are growing. They also spray their crops with pesticides to prevent rats, mice, and insects from contaminating foods while they are being stored.
While these actions are meant to benefit human health and bring a wide variety of fruits and vegetables to the supermarket, they can also harm people, wildlife, and the environment. This is why there are strict controls in place over their sale and use.
Air is a mixture of gases that circle Earth, kept in place by gravity. Air makes up Earth’s atmosphere. The air we breathe is 78 percent nitrogen gas, 21 percent oxygen, 0.9 percent argon, and 0.03 percent carbon dioxide, along with water vapor (floating molecules of water).
Also present are traces of other gases and tiny bits of dust, pollen grains from plants, and other solid particles. As our atmosphere extends higher and higher above Earth, toward outer space, air becomes thinner and the combination of gases in the air changes.
First built in 1960 by American physicist Theodore Maiman, lasers are machines that produce intense beams of high-energy light. Laser light is more powerful than ordinary light because all its rays have the same wavelength and move together in exactly the same direction, allowing them to be focused in a narrow beam with great precision.
Laser light beams vary in strength, depending on the materials and amount of energy used to make them. Lasers can melt, burn, or cut through a variety of different surfaces, from hard metal to the delicate human body, which is why they are often used in surgery today. Lasers can be used to make precise measurements, to reshape corneas to correct poor vision, to transmit telephone signals, to guide weapons, and to read supermarket bar codes.
Boats need a power source to move them forward in the water. In small vessels this power can be provided by people, who use oars to paddle along. Muscle power cannot move boats very fast or very far, though. The wind can be used, too, to move boats equipped with sails. But for a large boat that needs to go a long distance, the most reliable source of power is a motor-driven engine. Depending on the size of the boat, a gasoline engine, diesel engine, or steam engine does the job. Nuclear power is even used to run some boat engines, like those found in submarines. Motors rotate boat propellers, which have large twisting blades that radiate around a central hub.
These blades push water backward, and the boat moves forward as the disturbed water pushes back. Rotating propellers also create lower water pressure in the space in front of them, which sucks them forward, along with the vessel to which they are attached. (Using these same principles of movement, propellers can also power aircraft.) A boat is steered by a rudder, Which is a flat, upright, movable piece of wood or metal that is attached to its stern, or rear. When turned, the rudder changes the direction of the water around it, which pushes back, forcing the stern, and gradually the rest of the boat, to change direction, too.