Volcanoes
The earth's surface is composed of big slabs of rock called plates. Volcanoes are form...
The heart is an incredible organ. In vertebrates, it is a hollow muscular organ that pumps blood throughout the body. It pumps blood out of itself, and it takes blood into itself. All movement of blood in the body is caused by the heart. It brings oxygen and food to every part of the body. The heart is a specialized muscle. It is the only muscle that contracts and relaxes on its own. It beats at a regular rhythm or pulse. Waves of electrical stimulation pass through it, causing it to beat in this rhythmic pattern. The average human heartbeat, or rhythm, is 72 beats per minute. As a general rule, the larger vertebrates have slower heat rates while smaller vertebrates have faster heart rates. A hummingbird's heart rate averages 1,200 beats per minute. A Grey Whale's heart rate averages 9 beats per minute. No matter what the animal, the heart is an amazing organ.
The earth's surface is composed of big slabs of rock called plates. Volcanoes are form...
The South American Galapagos archipelago inspired Charles Darwin's theory of evolution...
Some of the world's most useful inventions are the result of failures. That's cert...