Cyanobacteria, also known as "blue-green algae", are the unicellular organisms which are able to produce oxygen.
Approximately 540 years ago, the atmosphere was very poor on oxygen. Cyanobacteria are thought to be responsible for the oxidization of the atmosphere back then, in an event known as <em>"The Great Oxygenation Event"</em>. As a result, Earth's life forms suffered drastic changes in their composition, as they evolved from being <em>anaerobic</em> to becoming organisms <em>highly dependant</em> on oxygen. The oxygenation of the atmosphere would eventually provide the adequate environment in order for the <em>Cambrian Explosion</em>, or the first diversification of living organisms, to happen.
What are the people or communities,
Spain, North Africa, Middle East, and much of Central Asia
General Ulysses S Grant wanted to wear down the Confederacy's forces, and cut the Confederate army off from supplies and food that would enable them to keep fighting.
<span>Grant knew that the Union had a superiority of numbers and supplies, while the South had no more soldiers in reserve and dwindling resources. If Grant and President Lincoln remained persistent, it was only a matter of time before the Confederacy would be placed in a position of surrender but at great cost to both sides in casualties. </span>
<span>Grant and the Army of the Potomac fought a series of battles against General Robert E Lee and his Army of Northern Virginia. Grant suffered losses of tens of thousands of men, but kept pushing Lee farther and farther south, also losing men every day. </span>
<span>One of Grant's strategies was to bring the war to the South, destroying resources and railroads and homes. Grant cut off Confederate supplies by sending forces into the Shenedoah Valley, the major food source of the Confederate armies. US General Philip Sheridan fought a series of battles against the outstanding defense of CSA General Jubal Early until Sheridan finally controlled the entire region and destroyed the South's major agricultural base. </span>
<span>Grant sent General William T Sherman on a similar mission farther south, beginning by capturing the major city of Atlanta. Sherman then marched across Georgia, destroying crops and railroads, all the way to the port of Savannah. Sherman then turned and marched north to approach Lee's army from the south. Lee's forces, depleted by casualties and desertions, were under intense pressure from all sides. Grant's forces began to win every encounter, US cavalry destroyed Lee's supply trains, and by April 9 of 1865 Lee surrendered his army to Grant. The surrender of the last Confederate army unit occurred in June of 1865.</span>
