what began the pliocene epoch?
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In addition to the Wikipedia answer already given, Episodes: Journal of International Geoscience indicates the Global Boundary Stratotype Section and Point (GSSP) for the Pliocene as being the base of the Trubi Formation (in Italy). At that location the change in stratigraphy marks the end of the Miocene and the start of the Pliocene. Worldwide climate changes and faunal succession at the time of deposition are among the reasons for a need to place an Epoch boundary at that level. The cause or causes of these changes are still largely speculation.\n\nThe primary marker for global correlation for this boundary is the insolation cycle (a cycle of well documented long term changes in the amount of energy reaching earth from the sun). Secondary markers include paleomagnetics (changes in the earths magnetic field recorded in the Earth's crust), along with the first appearance of some nannofossils and foraminifera and the disappearance of others. \n\nSo the simple answer is the same for this boundary as most other geological boundaries. Global changes in climate and life forms. Interestingly, changes you can observe the Earth undergoing at the present will likely make enough of a mark in the future geological record to deserve a new Geologic Period if not a whole new Geologic Era.
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Humanity, pre-history.
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~4.5 Billion years old.
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Pangea was the supercontinet - 180 million years ago that is. It broke out into Laurasia [ North America (Greenland), Europe, and Asia] and Gondwanaland (Antarctica, Australia, South America and India's subcontinet) through plate tectonics.
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Civilization begins with cities and writing.  Most historians agree that the first civilization began in Mesopotamia, often called "the cradle of civilization".\n\nAccording to recent archeological findings this early civilization began to florish around around 6000 BC.
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"The oldest indications for the existence of real land plants have been found in cores from boreholes in Oman. They contained fours of mutually connected spores (tetrads) enveloped by remains of the spore sac in which they had been formed. Research on the spore walls point to a relationship with the liverworts. The fossils have been found in the Middle Ordovician and are about 475 million years old."\n\nSee the link below for 2 pages of info on the development of this.
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Probably the age of ancient empires, though you should mention to your teacher that an archaeologist told you that none of those answers are very correct.
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About 250 million yrs.\n\nOne lap ago was the age of the dinosaurs.
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Around 4.57 billion years old.
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The origins of Chinese civilization started back more than 3500 years ago.
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It would be like the geological time frame of the Teriarty Period of the Cenozoic Era, which occurred 1.8 million years ago.  That period was filled with large and small mammals before the wooly mammuths & saber-tooth tigers.
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Global warming started long before the "Industrial Revolution" and the invention of the internal combustion engine. Global warming began 18,000 years ago as the earth started warming its way out of the Pleistocene Ice Age-- a time when much of North America, Europe, and Asia lay buried beneath great sheets of glacial ice.\n\nEarth's climate and the biosphere have been in constant flux, dominated by ice ages and glaciers for the past several million years. We are currently enjoying a temporary reprieve from the deep freeze.\n\nApproximately every 100,000 years Earth's climate warms up temporarily. These warm periods, called interglacial periods, appear to last approximately 15,000 to 20,000 years before regressing back to a cold ice age climate. At year 18,000 and counting our current interglacial vacation from the Ice Age is much nearer it's end than it's beginning.\n\nGlobal warming during Earth's current interglacial warm period has greatly altered our environment and the distribution and diversity of all life. For example:\n\n\n Approximately 15,000 years ago the earth had warmed sufficiently to halt the advance of glaciers, and sea levels worldwide began to rise.\n\n By 8,000 years ago the land bridge across the Bearing Strait was drowned, cutting off the migration of men and animals to North America.\n\n Since the end of the Ice Age, Earth's temperature has risen approximately 16 degrees F and sea levels have risen a total of 300 feet ! Forests have returned where once there was only ice.\n\nDuring ice ages our planet is cold, dry, and inhospitable-- supporting few forests but plenty of glaciers and deserts. Like a spread of collosal bulldozers, glaciers have scraped and pulverized vast stretches of Earth's surface and completely destroyed entire regional ecosystems not once, but several times. During Ice Ages winters were longer and more severe and ice sheets grew to tremendous size, accumulating to thicknesses of up to 8,000 feet!. They moved slowly from higher elevations to lower-- driven by gravity and their tremendous weight. They left in their wake altered river courses, flattened landscapes, and along the margins of their farthest advance, great piles of glacial debris.\n\nDuring the last 3 million years glaciers have at one time or another covered about 29% of Earth's land surface or about 17.14 million square miles (44.38 million sq. km.) . What did not lay beneath ice was a largely cold and desolate desert landscape, due in large part to the colder, less-humid atmospheric conditions that prevailed.\n\nDuring the Ice Age summers were short and winters were brutal. Animal life and especially plant life had a very tough time of it. Thanks to global warming, that has all now changed, at least temporarily.\n\nThje maximum CO2 level was 2% over 2.5 million yrs back, at least scientists say that!!
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This world STARTED when the last one ENDED.\nMeditate on it.
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http://en.wikipedia.org/wiki/Ice_age\nhttp://en.wikipedia.org/wiki/Timeline_of_glaciation
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We are currently nearing the warmest point in our meteorlogical history during the Holocine Epoch, the temperature will decrease quickly (geologically speaking) and we will enter an "ice age" in the next 40 million years.  The eventual glacial erosion, if substantial, will begin the next epoch.
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Tertiary, plaeocene to eocene (about 50 million years ago).\n\nOnly minor collisions occured earlier in the Cretaceous.
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A civilization is formed when a significant no. of people settle down in some particular area and start to grow food for themselves instead of hunting for it. \nFirst civilizations appeared in the plains between rivers Tigris & euphrates(present day Iran), the Nile valley(central Egypt); the Indus valley(India Pakistan border & its surroundings) & the Howang Ho-Yangste Kyang basin(North-central China). That of the tigris was the earliest starting in 3000 BC. The others started around 2500 BC.