Wednesday, March 11, 2020

how life began essays

how life began essays About 4.6 billion years ago the Earth was a fiery mass of liquid matter. As the hot mass began to cool, a rock crust formed on the Earth's surface, and the gases escaping from the newly made rocks formed the early atmosphere. The early atmosphere was made up of methane, ammonia, water vapor and hydrogen. There was no free oxygen in the early atmosphere. As the Earth cooled further the water vapor condensed, flooding the Earth with rain to form the oceans. Life begun in the harsh environments that dominated the early Earth, such as hot springs, submarine volcanic vents or in hot rocks deep within the Earth. Early forms of bacteria began to evolve about 3500-3800 million years ago, when there was little oxygen in the atmosphere. They produced energy using sources other than oxygen, such as nitrogen and sulfur compounds. Species similar to these early bacteria survive today and are found only in harsh environments, such as hot springs or deep in the Earth, where there is no oxygen. Oxygen is poisonous to these species. Some of the early bacteria evolved in a way to use the sun's energy to create a chemical reaction called photosynthesis. The earliest living things on Earth were primitive forms of bacteria. They were single-celled organisms with their genetic material free in their cells, not inside a nucleus. These types of cells are known as prokaryotes. About 1800 million years ago, new, complex, single-celled organisms evolved. They were called eucaryotes and had their DNA inside a nucleus, like the cells of most organisms today. Eucaryotes also had organelles inside the cell that performed a number of important functions. Some organelles are derived from free-living bacteria that became incorporated into, and formed beneficial relationships with, these early eucaryotes. ...

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