Hills are easier to climb than mountains. They are less steep and not as high. But, like a mountain, a hill will usually have an obvious summit, which is its highest point. According to the U.S. Geological Survey, there is no official difference between hills and mountains.
During the early earth, when photosynthesis has not yet evolved, there were only negligible amounts of free oxygen in the atmosphere. It was said that the Earth's atmosphere had no free oxygen then. This is about 3.5 billion years ago.
Eastern Europe. Communism was forced into Eastern Europe during WW2. Because of this, people state that being in a communist environment brought down the economy. Hope this helped!
4.54 billion years<span>The "best" age for the Earth is based on the time required for the lead isotopes in four very old lead ores (galena) to have evolved from the composition of lead at the time the Solar System formed, as recorded in the Canyon Diablo iron meteorite. This "model lead age" is <span>4.54 billion years</span></span>
