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How We Discover the Past?

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Presentation on theme: "How We Discover the Past?"— Presentation transcript:

1 How We Discover the Past?

2 The Evidence of the Past
Archeologists and Paleoanthropologists rely on four kinds of evidence to learn about the past: Artifacts Ecofacts Fossils Features Together they provide a detailed story about human life long ago.

3 Artifacts Anything made or modified by humans is an artifact.
Most of the artifacts that archeologists look for and examine to reconstruct what was daily life like long ago are accumulated garbage of daily life – This is called archaeological records.

4 Artifacts The most common artifacts from the past are stone tools, which archeologists call Lithics Humans first starting stone tools more than 2.5 million years ago. Used for almost every purpose.

5 Artifacts Another common artifact is ceramic (pots and other items of baked clay). Humans started making ceramics about 10,000 years ago. Because they are both fragile and relatively easy to make, ceramics show up frequently in the garbage that makes up the archeological record.

6 Artifacts Wood and bone artifacts are common as well.
Used to make hide-working, cooking, hunting and even butchering tools. Unlike stone tools they tend not to survive well in the archeological record.

7 Ecofacts Ecofacts are natural objects that have been used or affected by humans. For example: bones from animals that people have eaten. These bones are somewhat like artifacts, but they haven’t been made or modified by humans.

8 Fossils Rare but particularly informative about human biological evolution. A fossil may be an impression of an insect or leaf on a muddy surface that is now a stone.

9 Fossils Sometimes it is consist of the actual hardened remains of an animal’s skeletal structure. When an animal dies, the organic matter that made up its body begins to deteriorate. The teeth and skeletal structure are composed largely of inorganic mineral salts, and soon they are all that remains.

10 Fossils We don’t have fossil remains of everything that lived in the past, and sometimes we only have fragments from one or few individuals. Robert Martin established that the earth has probably seen 6,000 primate species. Remains of only 3% of these species have been found.

11 Features Features are a kind of artifact, but archaeologist distinguished them from other artifacts because they cannot be easily removed from an archaeological site. Hearths are good example, when humans build a fire on bare ground the soil becomes heated and is changes. When archaeologists finds a hearth, they find an area of hard, reddish soil often surrounded by charcoal and ash.

12 Features The most common features are called pits.
Pits are simply holes dug by humans that are later filled with garbage or eroded soil. Living floors are another common type of features. These are the places where humans lived and worked.

13 Features A large or very deep area of such debris is called a midden.
Midden are often the remains of garbage dumps or areas repeatedly used over long periods of time, such as caves. Buildings are a common feature on archaeological sites.

14 Finding the Evidence Evidence of the past is all around us, but finding them is not always easy. Archaeologists and paleoanthropologists usually restrict their search to what is called sites. Sites are know or suspected locations of human activities in the past that contain a record of that activity.

15 How Are Sites Created? Sites are created when the remnants of human activity are covered or buried by some natural process. The most dramatic one is volcanic activity. The records of human behavior or humans themselves can be totally buried within seconds. The most impressive example of this must be Pompeii – an entire city that was buried in the eruption of Mount Vesuvius in A.D. 79. Today archaeologists are digging out the city and finding the remains of ancient life just as it was left in the moments before the eruption.

16 How Are Sites Created Less dramatic means of burring the record of human behavior are the natural processes of dirt accumulation and erosion. Wind and water-borne soil and debris can cover a site either quickly (as in a flood) or over a long period of time. The processes through which soils are built up can also bury artifacts in a way that allows archaeologists to uncover them later.

17 How Are Sites Created Since good locations to live and work in are often reused by humans, many sites contain the remains of numerous human occupations. Stratified: each layer, or stratum, of human occupation is separated like a layer in a cake.

18 How Are Sites Created Not only do stratified sites allow the archaeologist or paleoanthropologists to distinguish the sequence of site occupations, but the strata themselves provide a way to know the relative ages of the occupations – earlier occupations will always be below later ones.

19 Taphonomy The very processes that create sites can often damage or destroy them. Wind and water for example. Harold Dibble and his colleagues, for example, have argued that the Lower Paleolithic site of Cagny-L’Epinette in France does not actually contain locations where Lower Paleolithic people lived and worked. What looks like locations of human activities were created by water running across the site and accumulating artifacts in low-lying places. The study of the processes of site disturbance and destruction is called Taphonomy.

20 How Are Sites Found? There is no single methods of finding sites, and indeed many sites are found by happenstance. Archaeologists and paleoanthropologists employ one of two basic methods: Pedestrian Survey: Walking around and looking for sites. Remote sensing: Much more high-tech way of finding sites.

21 Pedestrian Survey A number of techniques are used to enhance the effectiveness of pedestrian survey. Use of sampling and systematic surveying methods to reduce the area to be covered by foot. By focusing their search on places humans are likely to have occupied.

22 Remote Sensing Archaeologists find archaeological deposited by sensing their presence from a remote location, usually the current surface of the ground beneath which the archaeological deposits are buried. Most remove sensing techniques are borrowed from exploration geology, and are the same ones geologists use to find mineral or oil deposit.

23 How Are Artifacts Recovered from Sites?
Only one way to recover artifacts and fossils –excavation. Excavation is a complex process with two goals: To find every scrap of evidence. To record the horizontal and vertical location of that evidence with precision.

24 How Are Artifacts Recovered from Sites?
Few sites can even be fully excavated. The cost involved would be tremendous, and most archeologists feel it is important to leave some archeological deposits undisturbed for future archaeologists using new techniques. As a result archaeologists usually use some method of sampling.

25 How Are Artifacts Recovered from Sites?
Sampling however requires that archaeologists carefully plan where excavations will be conducted so that all areas of the site have an equal likelihood of being examined.

26 How Are Artifacts Recovered from Sites?
To date, no one has figured out a way to recover artifacts and fossils without destroying the site in the process. For this reason most excavation by professional archaeologists today is done only when a site is threatened with destruction.

27 Analyzing the Evidence

28 Analyzing the Evidence
Once archaeologists have found a site and recovered artifacts and other materials from it, they are ready to begin “reading” what they have found to learn the story of the past. The reading of the archaeologists is called analysis.

29 Analyzing the Evidence
Much of what is lost and discarded by humans never survive. Much of what does survive comes to us in fragments and in a fragile, deteriorated state. Before doing analysis, then, archaeologists and paleoanthropologists must first conserve and reconstruct the materials they have found.

30 Conservation and Reconstruction
Conservation is the process of treating artifacts to stop decay and if possible, reverse the deterioration process. Some conservation is very simple, involving only cleaning and drying the item. Some conservation is highly complex, involving long- term chemical treatment and long-term storage under controlled conditions. The 5,000 year-old “Ice Man” found in 1993 has to be kept permanently in glacial-like conditions.

31 Conservation and Reconstruction
Reconstruction is like building a three-dimensional puzzle where you’re not sure which pieces belong and you know not all of the pieces are there. First, archaeologists typically examine the form or shape of an artifact. For most common artifacts, such as ceramics, forms are known well enough to be grouped into a typology or set of types, which is the primary purpose of formal analysis. Typology provide a lot of information about the artifact, including: Its age Species and culture where it comes from. Sometimes, how it was made, used, or exchanges.

32 Conservation and Reconstruction
Reconstruction is like building a three-dimensional puzzle where you’re not sure which pieces belong and you know not all of the pieces are there. Second, archaeologists often measure artifacts, recording their size in various, often strictly defined, dimensions. This is called metric analysis. Third, archaeologists, often attempt to understand how an artifact was made. By examining the materials the artifact is made from and how that material was manipulated, archaeologists can learn about the technology, economy, and exchange system of the people who made the artifact.

33 Conservation and Reconstruction
Reconstruction is like building a three-dimensional puzzle where you’re not sure which pieces belong and you know not all of the pieces are there. Finally, archaeologists attempt to understand how an artifact was used. Knowing how an artifact was used gives the archaeologist a direct window onto ancient life. For stone, bone and wood tools, there is a technique called use-wear analysis which can determine how a tool was used through the careful examination of the kind of wear on its edges.

34 Conservation and Reconstruction
Knowing how an artifact was made allows the archaeologists to understand the technology and technical abilities of people in the past. For example: Thomas Wynn analyzed both the final forms and the methods used by early humans – Homo erectus – to make stone tools roughly 300,000 years ago. He found that manufacturing these tools was a multistage process, involving several distinct steps and several distinct stone-working techniques to arrive at the finished product. He then took his information and evaluated it in term of measure of human cognitive ability developed by Jean Piaget, and concluded that the people who made these tools probably had organizational abilities similar to those of modern humans.

35 Conservation and Reconstruction
Knowing how an artifact was used allows the archaeologists to know something of people’s behavior and activities. Lawrence Keeley conducted detailed use-wear analyses on Acheulian hand axes made by Homo erectus peoples and found that they had a variety of uses. Some cut meat. Others for wood To dig in the group (probably for edible roots). Therefore hand axes appear to have been multipurpose tools for our Homo erectus ancestors – something like a Swiss Army knife.

36 What Can We Learn from Ecofacts and Fossils
Ecofacts are diverse, and what archaeologists and paleoanthropologists can learn from them is highly diverse as well. Paleontologists (studying humans or other species) can tell a great deal about an extinct animal from its fossilized bones or teeth, but that knowledge is based on much more than just the fossil record itself.

37 What Can We Learn from Ecofacts and Fossils
Paleontologists rely on comparative anatomy to help reconstruct missing skeletal pieces New techniques, such as electron microscopy, CAT scans and computer provide much information about how the organism may have moved about.

38 What Can We Learn from Ecofacts and Fossils
Chemical analysis of fossilized can suggest what the animal typically ate. Paleontologists are also interested in the surroundings of the fossil finds

39 What Can We Learn from Ecofacts and Fossils
Much of the evidence for primate evolution comes from teeth, which are the most common animal parts (along with jaws) to be preserved as fossils. Animals vary in dentition – the number and kinds of teeth they have, their size, and their arrangement in the mouth.

40 What Can We Learn from Ecofacts and Fossils
Dentition provides clues to evolutionary relationships because animals with similar evolutionary histories often have similar teeth. For example, no primates, living or extinct, has more than two incisors in each quarter of the jaw. That feature, along with others, distinguishes the primates from earlier mammals, which had three incisors in each quarter.

41 What Can We Learn from Ecofacts and Fossils
Dentition also suggests the relative size of an animal and often offer clues about its diet. For example, comparison of living primates suggested that fruit0eaters have flattened, rounded tooth cusps, unlike leaf- and insect- eaters, which have more pointed cusps.

42 What Can We Learn from Ecofacts and Fossils
Paleontologists can tell much about an animal’s posture and locomotion from fragments of its skeleton. Arboreal quadrupeds have front and back limbs of about the same length; because their limbs tend to be short, their center of gravity is close to the branches on which they move. They also tend to have long grasping fingers and toes.

43 What Can We Learn from Ecofacts and Fossils
Paleontologists can tell much about an animal’s posture and locomotion from fragments of its skeleton. Terrestrial quadrupeds are more adapted for speed so they have longer limbs and shorter fingers and toes. Disproportionate limbs are more characteristics of vertical clingers and leapers and brachiators (species that swing through the branches). Vertical clingers and leapers have longer, more powerful hind limbs, branchiators have longer forelimbs.

44 What can we learn from Features?
Because we cannot remove features to the lab, we cannot subject them to the same range of analyses as artifacts, ecofacts, and fossils. Archaeologists developed a number of powerful tools to analyze features in the field. The primary one is detailed mapping, usually using a surveyor’s transit. Geographic information system (GIS) allow the archaeologist to produce a map of the features on a site and combine that map with information about other archaeological materials found there.

45 Putting It All in Context
Archaeologists do not study fossils and artifacts as individual objects. They put all the materials discovered in one site in context. This means how and why are the artifacts and other materials are related – This is what archaeology is all about. Fossils and artifacts maybe beautiful or interesting by themselves, but it is only when they are placed in context with the other materials found on a site that we are able to “read” and tell the story of the past.

46 Dating the Evidence An important part of putting artifacts and other materials into context is putting them in chronological order Dating methods include: Relative dating is used to determine the age of a specimen. Absolute dating or chronometric dating is used to measure how old a specimen or deposit is in years.

47 Relative Dating Methods
Stratigraphy The study of how different rock and solid formations are laid down in successive layers or strata. Oldest layers are generally deeper or lower than more recent layers. The earliest, and still the most common used. Indicator artifacts or ecofacts are used to establish a stratigraphic sequence. If a site has been disturbed, stratigraphy will not be a satisfactory way to determine relative age.

48 Absolute, or Chronometric Dating Methods
Many of the absolute dating methods are based on the decay of a radioactive isotope. Because the rate of decay is known, the age of the specimen can be estimated, within a range of possible error. Radiocarbon Dating or Carbon 14 dating The most popular known methods of determining the absolute age of a specimen. All living matter possesses a certain amount of radioactive form of carbon (Carbon 14). After an organism dies, it no longer takes in any of the radioactive carbon. Carbon-14 decays at a slow but steady pace and reverts to nitrogen-14. The rate at which carbon decays –its half life – is known: C-14 has a half life of 5,730 years

49 Absolute, or Chronometric Dating Methods
Thermoluminescence Dating Many minerals emit light when they are heated. This cold light comes from the release, under heat, of “outside” electrons trapped in the crystal structure. Thermoluminescence dating makes use of the principle that if an object is heated at some point to a high temperature it will release all the trapped electrons it held previously. The amount of Thermoluminescence emitted when the object is tested during testing allows researchers to calculate the age of the object. Thermoluminescence dating is well suited to sample of ancient pottery, brick, tile, and other objects that are made at high temperatures.

50 Absolute, or Chronometric Dating Methods
Electron Spin Resonance Dating Measures trapped electrons then expose them to magnetic fields. Paleomagnetic Dating When rock of any kind form, it records the ancient magnetic field of the earth. Since the earth’s magnetic field has reversed itself many times, the geomagnetic patterns in rocks can be used to date the fossils within the rocks.

51 Absolute, or Chronometric Dating Methods
Potassium-Argon Dating Potassium-40 decays at an established rate and forms argon-40. The half-life of K-40 is a known quantity, so the age of a material containing potassium can be measured by the amount of K-40 c0mpared with the amount of Ar-40. Potassium-Argon Dating us used to date samples from 5,000 years up t0 3 billion years old

52 Absolute, or Chronometric Dating Methods
Uranium-Series Dating The decay of two kinds of uranium U-235 and U-238 into other isotopes. Used especially in caves where stalagmites and other calcite formations form, because water usually contains uranium but not thorium. Fission-Track Dating It entails counting the number of paths or tracks etched in the sample by the fission-explosive division- of uranium atoms as they disintegrate.

53 The Results of Archaeological Research
One goal is the description or reconstruction of what happened in the past. Archaeologists attempt to determine how people lived in a particular place at a particular time, and when and how their lifestyle chance Another goal is testing specific explanations about human evolution and behavior. Understand general trends and patterns in human biological and cultural evolution.

54 Ethics in Archaeological Research
Archaeology does not simply describe past cultures. It can also have a profound effect on living people. For example, many people find the idea of archaeologists excavating, cleaning, and preserving the remains of ancestors to be offensive. Therefore, archaeologists must be sensitive to the desires and beliefs of the populations that descend from the ones they are researching.

55 Ethics in Archaeological Research
Artifacts from some ancient cultures are in great demand by art and antiquities collectors, and archaeological digs can lead to uncontrolled looting if archaeologists are not careful about how and to whom they report their discoveries. Archeologists must report all their findings to the public. Since by excavating a site, they damage it, they must document everything for future archaeologists who are excavating the same site.

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