Most people think that Mercury is the hottest planet because it is nearest to the Sun. However, Venus, the second nearest planet, is the hottest because it has an atmosphere. Its atmosphere is primarily composed of carbon dioxide, which acts like a greenhouse.
The solar heat enters Venus’s atmosphere, but it cannot leave, heating the planet’s surface to about 900 degrees Fahrenheit (482 degrees Celsius). This temperature is hot enough to melt several metals, including lead, tin, and zinc.
Yes. In 1997 a team of scientists at the Roslin Institute in Edinburgh, Scotland, announced the birth of Dolly the sheep, the first clone (identical copy) of an adult mammal. The process used to create Dolly, called somatic cell nuclear transfer, began with an egg cell from one sheep. The scientists destroyed that egg cell’s nucleus and then injected the nucleus from the cell of another sheep into the egg cell. With a little encouragement from electronic stimulation, the donated nucleus fused with the egg cell, and the new cell began to divide.
The cluster of cells was then implanted into the uterus of the sheep that had provided the egg cell, and five months later Dolly was born—an exact replica not of the sheep that had carried her in the womb but of the sheep that had supplied the nucleus. While cloning mammals is very controversial, some scientists argue that cloning farm animals has advantages to livestock farmers, who could use the technology to breed only highquality animals that produce the most milk or the finest wool.
Oxygen is necessary for all humans, animals, and plant life to survive. When Earth was first formed, its atmosphere had no oxygen—the colorless, odorless and tasteless gas that makes up about 20 percent of the air we breathe. It had only a deadly combination of hydrogen, methane, ammonia, and hydrogen cyanide.
The hydrogen escaped into space and ultraviolet radiation from the Sun broke down the mixture, leaving only nitrogen and carbon dioxide. Only when life began and photosynthesis (the conversion of light energy into chemical energy by living organisms) occurred did oxygen first appear—about 3.4 billion years ago.
The lizard is a reptile, a cold-blooded animal that is unable to internally control its own body temperature. In order to warm up or cool down, lizards and other reptiles—such as snakes, turtles, and crocodiles—move to different areas of their environment. They also use certain other behavioral traits to keep their body temperatures constant. For instance, if a lizard is starting to feel the intensity of the tropical sun, it might head into the shade or take a dip in a pool of water. The same lizard might also bask in the sun to warm up. Frilled dragons and collared lizards run on their hind legs in the heat of the day, making an artificial breeze to help cool themselves off. And another reptile, the crocodile, holds its jaws open to cool down on hot days.
The blood vessels in its mouth are close to the skin surface, and help transfer heat. Lying quietly is another technique the crocodile uses to warm its body and help digest its food. Because they are cold-blooded, reptiles can survive on much less food, compared to warm-blooded small mammals and birds, which burn much of their food to keep warm.
Today there are some 4,300 religions in the world. Nearly 75 percent of the world’s population practices one of the five most influential religions of the world: Christianity, Buddhism, Hinduism, Islam, and Judaism. Christianity, which is based on the teachings of Jesus Christ, who preached in Palestine about 2,000 years ago, is the most widely practiced religion in the world today, with 2.1 billion followers.
The second most practiced religion is Islam, with 1.3 billion followers.
Lots of kids have been picked on by a bully, for many different reasons. Bullying is intentional tormenting in physical, verbal, or psychological ways, and can range from hitting, shoving, name-calling, threats, and mocking to taking lunch money or personal items. If you’ve been the target of a bully, you know it can be very scary and upsetting to be teased, hit, or threatened.
Sometimes it helps to simply ignore what the bully is saying—most bullies tease or threaten other kids to get a reaction from those they tease, and if they get no reaction at all, it’s a lot less fun for them. It usually helps to have friends around. A kid walking alone is more vulnerable than a group of kids. And even if you don’t feel confident, sometimes acting confident helps. If you hold your head high and tell a bully to stop calling you names, you may just surprise that bully into silence. One approach to avoid is responding to bullying with fighting or bullying back—aggressive responses will only make matters worse.
Located at 0 degrees longitude, the prime meridian passes through Greenwich, England. Halfway around the world in the middle of the Pacific Ocean (180 degrees from Greenwich) is the International Date Line (IDL), where the date changes across the boundary of the time zone.
The entire world is on the same date only at the instant when it is noon in Greenwich, England, and midnight at the IDL. At all other times, there are different dates on each side of the IDL.
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.
Almost 10 percent of a cat’s bones are in its tail, and the tail is used to maintain the animal’s balance. A cat’s tail plays a vital part in its “righting reflex” that allows it to land on its feet after falling from a height. Cats often survive a long fall based on their agility and balance, which they develop as kittens. When falling, the fluid in the inner ear shifts and the cat rotates its head until it equalizes and the fluid is level.
The body automatically shifts to follow the head, and the cat lands on its feet. A cat also uses its tail to communicate. A cat’s tail held high means that it is happy. A twitching tail is a warning sign that it may be angry or on guard, and a tail tucked in close to the body is a sign of insecurity or fearfulness.
Many volcanoes occur near the area where two ridges or plates of Earth’s crust meet. Circling the Pacific Ocean—where crust plates meet—is a group of volcanoes known as the Ring of Fire. Plate movement in such regions may allow liquid rock, called magma (it’s called “lava” only after it rises to the surface), that is located in chambers in Earth’s interior to rise, resulting in volcanic activity. (Such conditions often result in earthquakes as well.)
Volcanic activity can take place under the ocean as well as on land, and when this happens the formation of islands sometimes results.