Define the moment our ancestors crossed the threshold into humanness

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partA.

1 Provide an example of both relative and absolute dating techniques.

2 Explain how we define the moment our ancestors crossed the threshold into humanness

(150~350 words - please cite any resources used)


partB.

Describe the contributions of investigations at Olduvai Gorge to paleoanthropological research.

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How is the past dated There are two primary techniques used to determine the age of fossils or related materials: relative and absolute. Relative dates are based on the arrangement of artifacts or events in a sequence. Dates produced with this measurement are relative to one another but lack ties to calendrically measured time. As a result, relative dates are expressed as a range of time (date and +/years). One example would be the arrangement of artifacts or fossils in a typological sequence or seriation based on stratigraphic analysis. Age is inferred based on the evidence surrounding the deposit/artifact/fossil. Here is an example of stratigraphic layers at an archaeological site in Canterbury. The same method applies to paleoanthropological efforts. Unless intrusion has occurred, generally, the deeper levels will be the oldest because they were deposited first. By contrast, absolute (chronometric) dating methods rely on measurements derived from processing chemical, organic, or radiometric material. These are accurate and precise but do not always reflect when human interaction occurred. Some of these techniques can date rock material but that does not differentiate when a rock might have been shaped into a tool. Carbon dating is a well-known absolute method of dating based on the decay rate of the half-life of carbon isotopes. It is important to remember that each technique has strengths and weaknesses. When dating paleontological material, the greater the number of techniques and dates that can be determined about a site or find, the stronger the evidence to support conclusions based on those discoveries. Here is a hypothetical C14 dating sample. The textbook lists many of the most common dating techniques and methods but there are tons of others, some quite unusual, you are welcome to explore. For example, let's consider that not all hominid characteristics evolved at the same time. The act of becoming human was a process of adding different components such as bipedalism, the manipulation of objects into tools, the physiological expansion of the brain, etc. These events occurred at different times in the history of hominin development...so… trying to determine the actual moment when our ancestors became recognizable as humans is complex. This is a highly contentious argument - you'll find different answers dependent upon identifying criteria. Hominid Origins Definition of Hominid Large brain size Australopithecus afarensis Becoming Human Learning Center, Calculating Cousins Definition of Hominid Tool making behavior Becoming Human Culture, No. 3 – Making Tools Definition of Hominid Bipedal locomotion All the major structural changes required for bipedalism are seen in early hominids from East and South Africa. Laetoli footprint Walking Tall Bipedalism Patterns of Evolution Mosaic evolution  Evolutionary pattern in which physiological and behavioral systems evolve at different rates. Biocultural evolution  Biology makes culture possible and developing culture further influences biological evolution. Evolving Ideas How do we know evolution happens? Paleoanthropology Paleoanthropologists reconstruct the anatomy, behavior, and ecology of our ancestors:  Geologists work with anthropologists to locate potential early hominid sites.  Archeologists excavate the site and search for hominid traces. Becoming Human Prologue Australopithecus africanus Hominids appear in the fossil record following the long development of primate adaptive radiation. Dating Methods Paleoanthropologists use two types of dating methods to tell us the age of sites and fossils:  Relative dating determines only whether an object is older or younger than other objects.  Chronometric (absolute) dating provides an estimate of age in years based on radioactive decay. Relative Dating Techniques  Stratigraphy - based on the law of superposition, that a lower stratum (layer) is older than a higher stratum.  Fluorine analysis applies to buried bones and groundwater seepage bones incorporate fluorine during fossilization. Relative Dating Techniques  Biostratigraphy related to changes in the dentition of animals.  Paleomagnetism based on the shifting of the geomagnetic pole. Chronometric Dating Techniques  The age of an object can be determined by measuring the rate of disintegration:  Potassium/argon (k/Ar) dating involves the decay of potassium into argon gas. K/Ar has a half-life of 1.25 billion years.  Carbon-14 is a radiometric method commonly used by archeologists. Carbon 14 has a halflife of 5730 years. Becoming Human Evidence Paranthropus boisei Primate Speciation  The first evidence of primate speciation occurs 65mya.  The first evidence for the appearance of early hominids is much more recent. Becoming Human Anatomy Paranthropus Boisei The Primate Descendency  Primates appear in the fossil record after the beginning of the Cenozoic Era.  Prosimians thrive during the Paleocene & Eocene.  Monkeys become dominant by the Oligocene.  Apes evolve by the Miocene.  In the late Miocene, the hominid evolutionary line finally becomes distinct – and includes our direct ancestors. Did Humans Evolve? PBS Evolution The East African Rift Valley  Known for mountain building, faulting and volcanic activity over the last several million years.  Early sediments were thrown to the surface where they were located by paleoanthropologists.  Volcanic sediments make it possible to chronometrically date the sites. Becoming a Fossil “Lucy” Earliest Traces of East African Hominids  The oldest specimen that is believed to be a hominid comes from Lothagam, northern Kenya.  Several other fragmented specimens have been found around the same area of east Africa Origins of Humankind Paranthropus boisei Aramis  Dated at 4.4 million years old, this is the oldest collection of hominids discovered.  The remains provide anatomical evidence of bipedalism, the criterion for hominid status.  The excavators suggested that the Aramis hominids be assigned to a new genus and species, Ardipithecus ramidus. Australopithecines Laetoli  Dated between 3.5-3.7 mya.  Fossilized hominid footprints found in an ancient volcanic bed.  The individuals were bipedal, but maybe not in the same way as modern humans. Laetoli Footprints Hadar (Afar Triangle)  Dating suggests a range from 3.9-2.3 mya  Recovered:  "Lucy" an Australopithecus afarensis female, was recovered here.  Group of bones representing 13 individuals, including 4 infants, suggest a social unit died at the same time.  Stone tools that may be 2.5 million years old, making them the oldest cultural evidence. Finding Lucy Bouri (Middle Awash)  Several fossils were discovered dating to 2.5 mya  These fossils are quite different from other PlioPleistocene hominids:  Projecting face  Very large back teeth  Long hind limbs  Animal bones found with these fossils show clear signs of butchering. Koobi Fora (East Lake Turkana)  This site yielded the richest assemblage of Plio-Pleistocene hominids from the African continent.  Most of the hominids date to 1.8 mya, others date back to 3.3 mya.  The 150 hominid specimens recovered at Koobi Fora in Kenya represent at least 100 individuals. West Turkana Two important discoveries:  The nearly complete 1.6 mya Homo erectus adolescent.  The black skull, a well-preserved 2.4 million year old skull which caused a major re-evaluation of Plio-Pleistocene evolution. Olduvai Gorge  Louis and Mary Leakey conducted continuous excavations from the 1930's to early 1980.  Paleontological evidence includes more than 150 species of extinct animals which can provide clues to the ecological conditions of early hominid habitats. Central Africa  A hominid mandible was discovered in Chad dating from 3.5 to 3.0 mya.  Preliminary analysis suggests that this fossil's closest affinity is to Australopithecus afarensis.  The fossil was found more than 1,500 miles west of the previously established range of early hominids. Australopithecus afarensis South African Sites  The first australopithecine was discovered at a quarry at Tuang.  As the number of discoveries accumulated, it became clear that the australopithecines were not simply aberrant apes.  The acceptance of the australopithecines as hominids required revision of human evolutionary theory. Groups of Plio-Pleistocene Hominids  Specimens represent 200 individuals from South Africa and more than 300 from East Africa.  Divided into four broad groupings:  Set I Basal Hominids.  Set II Early Primitive Australopithecus.  Set III Later, more derived Australopithecus.  Set IV Early homo. Becoming Human Lineages, No. 3 - The Human Family Tree Estimated Body Weights and Stature in Plio-Pleistocene Hominids Body Weight Stature Male Female Male Female A. afarensis 99 lb 64 lb 59 in. 41 in. A. africanus 90 lb 65 lb 54 in. 45 in. South African “robust” 88 lb 70 lb 52 in. 43 in. East African “robust” 108 lb 75 lb 54 in. 49 in. H. habilis 114 lb 70 lb 62 in. 49 in. Set I. Basal Hominid (4.4 mya)  The earliest and most primitive remains are those from Aramis.  They have been classified as Ardipithecus ramidus, a different genus from all other PlioPleistocene forms. Set II. Early Primitive Australopithecus (4.2-3.0 mya)  The hominids from Laetoli and Hadar are assigned to Australopithecus afarensis.  A. afarensis is so primitive in the majority of dental and cranial features that if it were not for evidence of bipedalism, this primate would not be classified as a hominid. Set III. Later, More Derived Australopithecus (2.5-1.0 mya)  Robust Australopithecines  Larger body size  Small cranial capacities  Very large, broad faces  Massive back teeth and lower jaws  Gracile Australopithecines  Different face dentition Set IV. Early Homo (2.4-1.8 mya)  The earliest appearance of our genus, Homo may be as ancient as the robust Australopithecines.  Leakey named these specimens Homo habilis ("handy man").  H. habilis differs from Australopithecus in cranial cavity and dental proportions. Becoming Human Lineages What we know…
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