Sunday, March 21, 2010
"Chemical History of the Earth" Coach O's period 4 class
The earth has a 4.5 billion year history. During this time major events have shaped the planet and the evolution of life. Students should research the history of the earth focusing on key chemical events and transformations. Provide a comment.
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One of the most important chemical events in the Earth's history is the creation of the ozone layer. The ozone layer is a layer of Earth's atmosphere that contains high amounts of ozone, a chemical that is formed when ultraviolet light hits oxygen. It was created hundreds of millions of years ago, back when the Earth lacked oxygen, and was only inhabited by single-celled organisms. However, these organisms began to evolve and release oxygen into the atmosphere. As ultraviolet light hit the oxygen, ozone was created. Although the ozone layer has been around for hundreds of millions of years, it wasn’t “discovered” until 1913 by French scientists Charles Farby and Henri Buisson. In the 1930’s, another scientist named Sidney Chapman produced a theory describing how ozone was created. He figured out that oxygen molecules can split in half when hit by ultraviolet light, and that when one of these atoms attaches to another oxygen molecule, it becomes ozone. The discovery of the ozone layer is important to Earth’s chemical history because without the ozone layer, organisms would have no protection against the sun, since the ozone layer absorbs anywhere from 93-99% of all ultraviolet light.
ReplyDeleteThe history of the earth describes the most important events and fundamental stages in the development of the planet Earth from 4.5 billion years ago to today. Nearly all branches of natural science have contributed to the understanding of the main events of Earth’s past. Major events, transformations, geological and biological changes have occurred during this time span. The main points that will be focused in this blog is the Hadean and Archaean periods, and events that have occurred in that time.
ReplyDeleteFirst of all, the earth formed by accretion of solid and particulate material that remained after the much more massive amounts of hydrogen and helium present in the original protoplanets had been dispersed out of the solar system. Gradually over time, the heat produced by decay of radioactive elements brought about partial melting of the silicate rocks. These lower density molten materials moved upward, leaving the denser, iron-containing minerals below. This process was the first of the three stages into which the chemical evolution of the earth is usually divided. It is divided into Primary Differentiation of the elements between the core and mantle. It is next divided into Secondary Differentiation of the elements, which reflects relative ionic sizes, bonding properties, and solubility’s. Finally is Tertiary differentiation, which is still operative, involving the interaction of the crust with the hydrosphere and atmosphere.
The first eon in Earth’s history is called the Hadean. It lasted until the Archaean eon, which began 3.8 Ga. The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in some rocks have been dated to about 4.4 Ga, close to the formation of the Earth's crust and the Earth itself. Since not much material from this time is preserved, little is known about Hadean times. It is hypothesized though, that at an estimated 4.53 Ga, shortly after the formation of the internal crust, the proto-Earth was impacted by a smaller protoplanet which ejected part of the mantle and crust into space and created the Moon. During this period, the Earth’s surface was bombarded by meteorites, and volcanism was severe due to the large heat flow and geothermal gradient. The detrital zircon crystals show evidence of having undergone contact with liquid water, considered as proof that the planet already had oceans or seas at that time.
By the start of the Archaean Period, the Earth had cooled down significantly. Due to the composition of the Archaean atmosphere it would have been impossible for most present day life forms to exist because of the lack of oxygen and absence of an ozone layer. It is believed that primitive life began to evolve by the early Archaean, with some possible fossil finds dated to around 3.5 GA.
Mantle convection, the process that drives plate tectonics today, is a result of heat flow from the core to the Earth’s surface. It involves the creation of rigid tectonic plates at mid-oceanic ridges. The plates are destroyed by subduction into the mantle at subduction zones. Inner earth was the warmest during the Archaean and Hadean eons, so convection in the mantle was faster. Most geologists think that during the Hadean and Archaean, subduction zones were more common, and therefore tectonic plates were smaller. The initial crust totally disappeared from a combination of Hadean plate tectonics and the impacts of the Late Heavy Bombardment. It is assumed that the crust must have been basaltic in composition, like today’s oceanic crust, because little crustal differentiation had yet taken place. The first larger pieces of continental crust, which is a product of differentiation of lighter elements during partial melting in the lower crust, appeared at the end of the Hadean, about 4.0 Ga.
The Earth is around 4.5 billion years old, and yet humans have only seen a glimpse of it’s time. The first eon in the Earth's history is called the Hadean. During the Hadean, the Earth's surface was under bombardment by meteorites, and volcanoes were extremely active. More proof of this is the pillow basalts, and the deep marine seds in greenstone belts. The beginning of the Earth’s core and first atmosphere was rather extreme compared to what it is today. Earth’s core grew by accretion, until the inner part of the planet was hot enough to melt the heavy, siderophile metals. Due to their larger densities, metals began to sink to the Earth's center of mass. The iron catastrophe resulted in the separation of a primitive mantle and a core only 10 million years after the Earth began to form, producing the layered structure of Earth and setting up the formation of Earth's magnetic field. What was left surrounding the planet was an early atmosphere of light elements from the solar nebula, mainly hydrogen and helium. By the beginning of the Archaean Eon, the Earth had cooled considerably. Due to the composition of the Archaean atmosphere, it seemed to have been impossible for life forms to exist because it was composed of no oxygen and extremely harmful chemicals such as H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3 and CH4.An important event in Earths timeline was the impact of Earth and a similar rendition of Mars The small planet, sometimes named Theia, collided with Earth about 4.533 billion years ago. The impact was great, and the materials that flew away from the Earth created the Moon. The radiometric ages show the Earth existed already for at least 10 million years before the impact, enough time to allow for differentiation of the Earth's primitive mantle and core. It is believed that this impact created the 23.5 axis tilt that gave us the seasons and also sped up the Earth’s rotation. It is assumed the water was derived from impacting comets that contained ice which bombarded the planet. Impacts of these objects enriched the Earth with water, carbon dioxide, methane, ammonia, and nitrogen. As the planet cooled, clouds formed. Rain created the oceans.The new atmosphere contained water vapor, carbon dioxide, and nitrogen, as well as smaller amounts of other gases The high energy from volcanoes, lightning and ultraviolet radiation helped drive chemical reactions producing more complex molecules from simple compounds such as methane and ammonia. Among these were many of the simpler organic compounds, including nucleobases and amino acids, which are the building blocks of life. As the amount and concentration of this “organic soup” increased, different molecules reacted with one another. Sometimes more complex molecules would result. Initial cells were all heterotrophs, using surrounding organic molecules As the food supply diminished, a new strategy evolved in some cells. Instead of relying on the diminishing amounts of free-existing organic molecules, these cells adopted sunlight as an energy source. This type of photosynthesis, which became by far the most common, used carbon dioxide and water as raw materials and, with the energy of sunlight, produced energy-rich organic molecules. Oxygen was released as a waste product of the photosynthesis. At first it became bound up with limestone, iron, and other minerals. The reaction of the minerals with oxygen would have turned the oceans green. When most of the exposed readily-reacting minerals were oxidized, oxygen finally began to build up in the atmosphere. Though each cell only produced minimal amount of oxygen, the combined metabolism of many cells over a vast time transformed Earth’s atmosphere to its current state. The most important transformation was Earth’s ozone layer. The advantage of an oxygen-rich atmosphere is that oxygen forms ozone in the higher atmosphere, causing the origin of the Earth's ozone layer. The combined events of the ozone layer, the evolution of life, and the transformation of the Earth’s crust made it for what it is today.
ReplyDeleteWhile forming the Earth was first a giant molten mass of metals. Metals such as nickel, iron, and silicon were sorted out into layers base on their density. When the Earth finally solidified it was barren, with a atmosphere of Hydrogen and Helium. These were heated by solar winds and eventually escaped. Volcanic activity did take place during this time and what is known as outgassing occurred. This aided in the creation of the atmosphere. As time passed the Earth was hit by Theia, a proto-planet one tenth of the Earth’s size, creating what is now called Luna. This is one of the, if not the most important event in the history of the earth. Without this collision the volatile substances in the soil wouldn’t have been released into the atmosphere, making it what it is today. When the two proto-planets hit several substances were released. Carbon dioxide, water, which formed creating Hydrogen Carbonate or acid rain. This then reacted with Calcium to produce Calcium Carbonate, or limestone. It also reacted with Calcium Magnesium carbonate to produce dolomite, a sedimentary carbonate mineral. Nitrogen(N2) was another of the substances released but, with it being inert it would stay in the atmosphere eventually creating the nitrogen cycle. The climate also created the perfect conditions. Instead of the carbon dioxide staying in the atmosphere it was pushed into the crust.
ReplyDelete-CO(2)+H(2)O H(2)CO(3)
-H(2)CO(3)+Ca CaCO(3)
- H(2)CO(3)+CaMg(CO(3))(2) dolomite
Today, scientists have found that volcanoes that 50-60% of the matter released from a volcano is water vapor. Even with the release of water vapor it still wouldn’t be enough to create the immense oceans we have now. Many asteroid also impacted the Earth bringing water to the planet in the form of ice. These impacts, sparked volcanic activity on the surface contributing to its primordial atmosphere.
The creation of amino acids was another monumental occurrence.
-NH3 + 2CH4 + 2H2O + energy = C2H5O2N + 5H2
-5H2CO = ribose
-5HCN + UV + NH3 = adenine(amino acid)
The oceans created the perfect environment for the amino acids, stopping the UV rays from disrupting processes. With the right conditions the monomers were able to create polymers, some of which were able to reproduce asexually. They were products of random combinations until the creation of DNA. They eventually evolved into prokaryotes that fed off of what was most abundant, CO2 and H2S. However, H2S took less energy to break down the by product of which was sulfur. This was the early form of photosynthesis. When there was little H2S left in the atmosphere the creation of chlorophyll helped organisms process H2O leaving O2 as the waste product. It takes a while for the oxygen to be introduced into the atmosphere, because the iron in the oceans reacted to form iron oxide. When oxygen is released into the atmosphere some of it creates ozone (O3), hence, the ozone layer.
O2 + O + M = O3
In this M is the density. Oxygen is then made available leading to eukaryotic cells and the process of mitosis, which resulted in the evolution of multi-cellular organisms.