Barack Obama - Seventh Weekly Transition Address free essay sample

Principle Events in the Evolution of Earths Atmosphere essays

Principle Events in the Evolution of Earth's Atmosphere essays The literal translation of the word atmosphere is "sphere of vapors." The Earth's atmosphere is a protective sphere of vapors or air that surrounds the Earth and provides it with a layer of insulation from the harmful rays of the sun. It is a vital part of the Earth and has changed dramatically since the beginning of time. The earth's atmosphere had gradually changed since the Earth's birth approximately 4.6 million years ago. In the beginning, Earth's composition was very different than how it exists today. A long time ago the Earth's atmosphere was very similar to today's Venus and Mar's atmosphere. It had about 95% carbon dioxide, 2-3% nitrogen, and very little, less than 1% oxygen. Today the Earth contains 79% nitrogen, 21% oxygen, and 3% water vapor. It is evident that many events happened over billions of years that have contributed to this change in the Earth's atmosphere. Earth had developed so drastically because of the large amounts of dust and gas cloud within the Milky Way galaxy. The Earth grew larger as huge meteorites hit it, and the surface was covered with dust. Volcanoes began to form and emitted lava, ash, and most importantly gases. Carbon dioxide, water vapor, and nitrogen were released into the atmosphere from the volcanoes. This process is called outgassing and took place within the first million years or so of the Earth's formation. Then, about 4 billion years ago, the planet cool ed, and the outgassed water vapors condensed into clouds. It rained and produced the oceans, and even enough to cover 95% of the Earth. Also, because it rained, there was less carbon dioxide in the atmosphere. The carbon dioxide was lost over billions of years, as the ocean formed there was a chemical reaction in which carbon dioxide and water formed carbonic acid. It is shown in the equation CO2 + H2O = H2CO3. The carbonic acid dissolved oceanic rock into sand, silt, and mud. It is evident because of this geochemical process occurre...

Venetian Altarpieces 1460-1505 Literature review

Venetian Altarpieces 1460-1505 - Literature review Example The altarpieces were often funded by the affluent Venetians, therefore the altarpieces, like the chapels that house them, were often meant as a celebration of the affluence and rank of these families. Seidel (1994) states that such patronage could be a family’s way of regaining prominence after it has returned from exile, or could be a way to celebrate enormous prosperity for the family. Humfrey (1994) states that, for instance, Jacopo Bellini’s altarpiece Annunciation was commissioned by the widow of Gattamelata, Giacomo da Leonessa. De Leonessa was closely associated with Donatello and was a patron of Mantegna. As such, she was at the forefront of the Renaissance art in Northeastern Italy, and she wanted her altarpieces to be as up to date as these other pieces. This meant that Jacopo Bellini would have had specific terms for his commission to construct the Annunciation. Rubin (1994) states that the subject of the painting was not usually left to the artist, but, rather, was decided by the patrons before the artist even begun working. The subject was decided before the artist was even chosen. The patrons would usually decide what it was that they were trying to convey, and calculated their needs and budget for the work accordingly. The patrons then set out to find a master to carry out their designs. The wills, bequests, and donations for these altarpieces usually stipulated that the paintings be carried out by a famous or skilled master. The painter could, however, embellish the painting as he saw as being necessary – for instance, the painter, such as Perugino, would add angels, ornaments and extra heads. However, these artists were not invented, so much as they were ornamenting or filling in the blanks for the patrons. It was all very workmanlike, according to Muraro (1994), in that the artist or the artist’s house would sign a detai led contract that would dictate which patron saints would be depicted, the time that would be allotted for the painting to be completed, the day for delivery of the painting, the information about arbitration in cases of dispute, and the forms of payment.