The Origin and Evolution of Life on Earth
Why do we start the discussion of biology with a discussion of geology? Here are some reasons why one would do this: * All life on earth is linked to geology; likewise, many surface geologic features and processes have been influenced by life on earth. The origin and early evolution of the earth are especially important when looking at the origin and early evolution of life on earth. * Life chemistry had its origin with the elements available to it during the formation of the earth. These provided the basic raw materials available for life. * The evolution of life is in response to changes in environment. Many of these changes are linked to changes in climate and/or geology. * All life is (so far) limited to placement upon the earth, so it is crucial that we understand the processes of the earth.
The Big Bang theory of the formation of the universe
All material in the universe was created in a huge "explosion," creating and defining matter and space. The sudden cooling of the superheated ejecta facilitated the combination of atomic components into atoms and molecules. These clouds of gasses eventually cooled and formed the principle components of galaxies - including stars and planets. Other theories have been postulated (i.e. the oscillating universe theory which states that the universe expands and contracts in a cycle every 100 billion years) and these are hotly debated
Location of the Solar System
Our solar system is located on a spiral arm of the Milky Way galaxy. We are approximately 2/3 of the distance from the core to the outer rim of the galaxy. This distance places us in a lower-density region of the galaxy - there are some stars near to ours, but this region is nowhere as congested as the galactic core.
Formation of the solar system
| A. The earth formed approximately 4.6 BYA (billion years ago.) Initially, there was a cloud of gasses and dust particles, possibly originating from the ejected particles of a nearby supernova. B. The cloud gradually contracted and flattened, concentrating about 99% of its mass in the center with the rest rotating counterclockwise in a flattened disk. C. As the disk rotated, turbulence was created, causing condensation of the disk into small, turbular eddies. These gradually accreted together to form protoplanets. D. These protoplanets further accreted, creating the mature planets of the solar system. The sun also accreted, pulling in most of the mass. As these accumulated, the pressure and temperature caused the initiation of thermonuclear fusion. This thermonuclear fusion is what provides the ultimate source of energy for all life on earth. In the hot accretions of planetesimals, iron-rich elements condensed first, creating the cores (the inner and outer cores). Next, the lower-density silicates began to condense and aggregate, forming the mantle and the crust. Further differentiation of the crust was fueled by the energy output from radioactive decay deep within the earth
Structure of the earth
| There are three clearly defined regions of the earth: * Cores (inner (1250 km) and outer (2100 km)) - composed primarily of iron (85%) and nickel. Other heavy elements (such as radioactive elements) are also found here * Mantle (2900 km) - a "fluid" region primarily composed of oxygen and silica - derived minerals * Crust (5-70 km) - thin film of "crud" which has floated to the surface. We are simply passengers, living on this geologic flotsam.
Early Earth Conditions
Theory of Early Earth Conditions-Hot and violent
* Immense heat due to accretion and volcanoes-Earth is molten. * Earth is bombarded by asteroids, one of which dislodged the moon. * Cooling causes condensation of H2O to form rain.
* Volcanoes eject gases (CO2, N2, H2), forming the early atmosphere. * Note that there is no O2 present in the early atmosphere. Any O2 outgassed would have reacted with the...
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