Formation. Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby exploding star, called a supernova. When this dust cloud collapsed, it formed a solar nebula—a spinning, swirling disk of material. Approximately 4.6 billion years ago, the solar system was a cloud of dust and gas known as a solar nebula. Gravity collapsed the material in on itself as it began to spin, forming the sun in the center of the nebula. With the rise of the sun, the remaining material began to clump together. Part of Hall of the Universe. The Sun and the planets formed together, 4.6 billion years ago, from a cloud of gas and dust called the solar nebula. A shock wave from a nearby supernova explosion probably initiated the collapse of the solar nebula. ... In a similar manner, moons formed orbiting the gas giant planets. Hope this helps!
The African countries can easily be described and generalized, in the sense of the whole continent, as the economies are predominantly dependent on one or two products.
That dependence on one or two products is making very big problems, and it is also a very big mistake of the governments. When there's a slight variation in the prices on the certain product, the economies are heavily influenced, often in a bed manner.
It is weird though that the African countries have orientated their economies in this way, especially because the continent is very rich in lots of natural resources.
Les systèmes fluviaux et les plaines inondables du Brésil, du Pérou, de l'Équateur, de la Colombie et du Venezuela, dont les eaux se déversent dans la Solimões et ses affluents, sont appelés "la haute Amazonie
The U.S. has more than 87,000 dams greater than six feet high (and two million overall). While many dams continue to provide benefits such as flood control, irrigation, and water supply, for other dams the cost of maintenance or the negative effects on communities, fish, and tribes justifies their removal.
Dam owners and regulators decide whether to remove a dam by weighing many factors including: the cost of removal and the ability to replace any lost power generation against avoided long-term maintenance; safety concerns; benefits to endangered fish populations; increased recreational and commercial fishing; and restoration of cultural values of nearby tribes.
By 2020, roughly 70% of dams will be more than 50 years old, inviting us to reconsider the value to the public of long-term investments in this infrastructure.
