Short History of the World Part 3.
Geologic time, the extensive interval of time occupied by the Earth’s geologic history. It extends from about 3.9 billion years ago (corresponding to the age of the oldest known rocks) to the present day. It is, in effect, that segment of Earth history that is represented by and recorded in rock strata.
The geologic time scale is the calendar for events in Earth history. It subdivides all time since the end of the Earth’s formative period as a planet (nearly 4 billion years ago) into named units of abstract time: the latter, in descending order of duration, are eons, eras, periods, and epochs. The enumeration of these geologic time units is based on stratigraphy, which is the correlation and classification of rock strata.
The fossil forms that occur in these rocks provide the chief means of establishing a geologic time scale. Because living things have undergone evolutionary changes over geologic time, particular kinds of organisms are characteristic of particular parts of the geologic record. By correlating the strata in which certain types of fossils are found, the geologic history of various regions (and of the Earth as a whole) can be reconstructed. The relative geologic time scale developed from the fossil record has been numerically quantified by means of absolute dates obtained with radiometric dating methods.
Following is a list of accepted terminology for Epoch Time Lines.
Precambrian Time (4567 to 542 million years ago)
Hadean Eon (4567 to 3800 million years ago)
Archaean Eon (3800 to 2500 million years ago)
Proterozoic Eon (2500 to 542 million years ago)
Paleoproterozoic Era (2500 to 1600 million years ago)
Siderian Period (2500 to 2300 million years ago)
Rhyacian Period (2300 to 2050 million years ago )
Orosirian Period (2050 to 1800 million years ago)
Statherian Period (1800 to 1600 million years ago)
Mesoproterozoic Era (1600 to 1000 million years ago)
Calymmian Period (1600 to 1400 million years ago)
Ectasian Period (1400 to 1200 million years ago)
Stenian Period (1200 to 1000 million years ago)
Neoproterozoic Era (1000 to 542 million years ago)
Tonian Period (1000 to 850 million years ago)
Cryogenian Period (850 to 630 million years ago)
Ediacaran (Vendian) Period (630 to 542 million years ago)
Paleozoic Era (542 to 251 million years ago)
Cambrian Period (542 to 488.3 million years ago)
Tommotian Stage (534 to 530 million years ago)
Ordovician Period (488.3 to 443.7 million years ago)
Silurian Period (443.7 to 416 million years ago)
Devonian Period (416 to 359.2 million years ago)
Carboniferous Period (359.2 to 299 million years ago)
Mississippian Epoch (359.2 to 318.1 million years ago)
Pennsylvanian Epoch (318.1 to 299 million years ago)
Permian Period (299 to 251 million years ago)
Mesozoic Era (251 to 65.5 million years ago)
Triassic Period (251 to 199.6 million years ago)
Jurassic Period (199.6 to 145.5 million years ago)
Cretaceous Period (145.5 to 65.5 million years ago)
Cenozoic Era (65.5 million years ago to today)
Paleogene Period (65.5 to 23.03 million years ago)
Tertiary Period (65.5 to 2.58 million years ago)
Paleocene Epoch (65.5 to 55.8 million years ago)
Eocene Epoch (55.8 to 33.9 million years ago)
Oligocene Epoch (33.9 to 23.03 million years ago)
Neogene Period (23.03 million years ago to today)
Miocene Epoch (23.03 to 5.3 million years ago)
Pliocene Epoch (5.3 to 2.58 million years ago)
Quaternary Period (2.58 million years ago to today)
Pleistocene Epoch (2.58 million years ago to 11,400 yrs ago)
Beginning of the Stone Age
In 2010, fossilised animal bones bearing marks from stone tools were found in the Lower Awash Valley in Ethiopia. Discovered by an international team led by Shannon McPherron, they are the oldest evidence of stone tool use ever found anywhere in the world.
The oldest known stone tools have been excavated from several sites at Gona, Ethiopia, on the sediments of the paleo-Awash River, which serve to date them. All the tools come from the Busidama Formation, which lies above a disconformity, or missing layer, which would have been from 2.9-2.7 million years ago. The oldest sites containing tools are dated to 2.6-2.55 million years ago. One of the most striking circumstances about these sites is that they are from the Late Pliocene, where previous to their discovery tools were thought to have evolved only in the Pleistocene. Rogers and Semaw, excavators at the locality, point out that:
“…the earliest stone tool makers were skilled flintknappers …. The possible reasons behind this seeming abrupt transition from the absence of stone tools to the presence thereof include … gaps in the geological record.”
The excavators are confident that more tools will be found elsewhere from 2.9 million years ago. The species who made the Pliocene tools remains unknown. Fragments of Australopithecus garhi, Australopithecus aethiopicus and Homo, possibly Homo habilis, have been found in sites near the age of the oldest tools.
Neanderthal man spreads through Europe
Neanderthal cranial capacity is thought to have been as large as that of modern humans, perhaps larger, indicating that their brain size may have been comparable, or larger, as well. In 2008, a group of scientists created a study using three-dimensional computer-assisted reconstructions of Neanderthal infants based on fossils found in Russia and Syria. The study showed Neanderthal and modern human brains were the same size at birth, but by adulthood, the Neanderthal brain was larger than the modern human brain. They were much stronger than modern humans, having particularly strong arms and hands. Males stood 164–168 cm (65–66 in) and females about 152–156 cm (60–61 in) tall.
Genetic evidence published in 2010 suggests they contributed DNA to anatomically modern humans, probably through interbreeding between Neanderthals and the earliest Humans that dispersed out of Africa. This is thought to have occurred between 80,000 and 50,000 years ago, shortly after (or perhaps before) the proto-Eurasians emigrated from Africa, while they were still one population. According to the study as much as 1–4% of the genome of the population that populated Eurasia was contributed by Neanderthals.
Homo sapiens reduced to about 10,000 individuals
The Toba supereruption (Youngest Toba Tuff or simply YTT was a supervolcanic eruption that is believed to have occurred sometime between 69,000 and 77,000 years ago at Lake Toba (Sumatra, Indonesia). It is recognized as one of the Earth’s largest known eruptions. The related catastrophe hypothesis holds that this event plunged the planet into a 6-to-10-year volcanic winter and possibly an additional 1,000-year cooling episode. This change in temperature is hypothesized to have resulted in the world’s human population being reduced to 10,000 or even a mere 1,000 breeding pairs, creating a bottleneck in human evolution.
Holocene Epoch (11,400 years ago to today)
5,300 yrs ago: The Bronze Age
The term “Bronze Age” ultimately derives from the Ages of Man, the stages of human existence on the Earth according to Greek mythology. Of these, modern historians categorize the Golden Age and Silver Age as mythical, but consider the Bronze Age and Iron Age historically valid. The overall period is characterized by the full adoption of bronze in many regions, though the place and time of the introduction and development of bronze technology was not universally synchronous. Man-made tin bronze technology requires set production techniques. Tin must be mined (mainly as the tin ore cassiterite) and smelted separately, then added to molten copper to make the bronze alloy. The Bronze Age was a time of heavy use of metals and of developing trade networks.
3,300 yrs ago: The Iron Age
The Iron Age is the archaeological period generally occurring after the Bronze Age, marked by the prevalent use of iron. The early period of the age is characterized by the widespread use of iron or steel. The adoption of such material coincided with other changes in society, including differing agricultural practices, religious beliefs and artistic styles. The Iron Age as an archaeological term indicates the condition as to civilization and culture of a people using iron as the material for their cutting tools and weapons. The Iron Age is the third principal period of the three-age system created by Christian Jürgensen Thomsen for classifying ancient societies and prehistoric stages of progress.
In historical archaeology, the ancient literature of the Iron Age includes the earliest texts preserved in manuscript tradition. Sanskrit literature and Chinese literature flourished in the Age. Other text includes the Avestan Gathas, the Indian Vedas and the oldest parts of the Hebrew Bible. The principal feature that distinguishes the Iron Age from the preceding ages is the introduction of alphabetic characters, and the consequent development of written language which enabled literature and historic record.
The beginning of the Iron Age in Europe and adjacent areas is characterized by certain forms of implements, weapons, personal ornaments, and pottery, and also by systems of decorative design, which are altogether different from those of the preceding age of bronze. The work of blacksmiths—developing implements and weapons—is hammered into shape, and, as a consequence, gradually departed from the stereotyped forms of their predecessors in bronze, which were cast, and the system of decoration, which in the Bronze Age consisted chiefly of a repetition of rectilinear patterns, gave way to a system of curvilinear and flowing designs. The term “Iron Age” has low chronological value, because it didn’t begin simultaneously across the entire world. The dates and context vary depending on the region, and the sequence of ages is not necessarily true for every part of the earth’s surface. There are areas, such as the islands of the South Pacific, the interior of Africa, and parts of North and South America, where peoples have passed directly from the use of stone to the use of iron without the intervention of an age of bronze.