High School Earth Science/Geologic Time Scale

High School Earth Science/Geologic Time Scale

Skeptical Inquirer Volume But a closer look at the evidence suggests otherwise. As long as there are lonely hearts there will be a market for matchmakers. The emergence of the Internet has of course revolutionized many things, and the search for compatible mates is no exception. Online dating is a huge business, with dozens of websites offering people the chance to find love in cyberspace. Like many services for which there is competition, online dating sites struggle to distinguish their services from all the others. After all, the premise is pretty basic:

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Dating techniques are procedures used by scientists to determine the age of an object or a series of events. The two main types of dating methods are relative and absolute. Absolute age dating is based upon the decay of radioactive unstable isotopes. The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of ‘relative different types of absolute dating as observed in geology from the 17th century to the early 20th century.

Cosmic-ray Exposure Dating: Overview of Scientific Dating Methods: Dating the Past: This is an excellent overview of dating methodologies, and is a chapter in a textbook on Archaeology. You may find it useful for the clear definitions, and for excellent links on a variety of topic.

January Fossils provide a record of the history of life. Smith is known as the Father of English Geology. Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods. Some critics, particularly religious fundamentalists, argue that neither fossils nor dating can be trusted, and that their interpretations are better. Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.

These skeptics do not provide scientific evidence for their views. Current understanding of the history of life is probably close to the truth because it is based on repeated and careful testing and consideration of data. The rejection of the validity of fossils and of dating by religious fundamentalists creates a problem for them: Millions of fossils have been discovered. They cannot deny that hundreds of millions of fossils reside in display cases and drawers around the world.

Perhaps some would argue that these specimens – huge skeletons of dinosaurs, blocks from ancient shell beds containing hundreds of specimens, delicately preserved fern fronds — have been manufactured by scientists to confuse the public. This is clearly ludicrous. Some skeptics believe that all fossils are the same age.

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Unlike the radioactive isotopes discussed above, these isotopes are constantly being replenished in small amounts in one of two ways. The bottom two entries, uranium and thorium , are replenished as the long-lived uranium atoms decay. These will be discussed in the next section. The other three, Carbon , beryllium , and chlorine are produced by cosmic rays–high energy particles and photons in space–as they hit the Earth’s upper atmosphere.

Very small amounts of each of these isotopes are present in the air we breathe and the water we drink.

They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years. This is different to relative dating, which only .

Like many viruses, HIV has the ability to mutate and change over time – within the main types of HIV there are many genetically distinct subgroups. Tests to diagnose HIV and monitor the level of virus in the body that are sensitive to the full range of subtypes and to group O and HIV-2 do exist, but may not be readily available in all settings. Although tests which are sensitive to both types of viruses are widely available, the significant genetic differences between the two types mean that a test specifically designed to detect one type will not reliably identify the other.

Worldwide, the predominant, earliest and most commonly referred to virus is HIV The relatively uncommon HIV-2 virus is concentrated in West Africa, but has been seen in other countries. It is less infectious and progresses more slowly than HIV-1, resulting in fewer deaths. The other three groups – N, O and P – are quite uncommon.

Dating techniques

Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age. Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers. Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.

For example, most limestones represent marine environments, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed.

Athletic, nerdy, spontaneous, social, calm, etc. — there’s no denying people have types when it comes to dating. But what’s behind these patterns that cause us to date the same person over and.

Love-hungry teenagers and archaeologists agree: But while the difficulties of single life may be intractable, the challenge of determining the age of prehistoric artifacts and fossils is greatly aided by measuring certain radioactive isotopes. Until this century, relative dating was the only technique for identifying the age of a truly ancient object. By examining the object’s relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.

Though still heavily used, relative dating is now augmented by several modern dating techniques. Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon content. Carbon , or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide. Green plants absorb the carbon dioxide, so the population of carbon molecules is continually replenished until the plant dies.

dating with science

In ancient times, fossils inspired legends of monsters and other strange creatures. The Chinese writer Chang Qu reports the discovery of “dragon bones”, which were probably dinosaur fossils in China 2, years ago. The griffin, a mythical creature with a lion’s body and an eagle’s head and wings, was probably based on skeletons of Protoceratops that were discovered by nomads in Central Asia Figure Griffin left and Protoceratops right. Another fossil reminded the Greeks of the coiled horns of a ram.

Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence. The method of reading the order is called stratigraphy (layers of rock are called strata). Relative dating does not provide actual numerical dates for the rocks.

Some background orientation will be useful before turning to the details of competing models. A presupposition of most recent discussion has been that science sometimes provides explanations rather than something that falls short of explanation—e. However, with respect to the first contrast, the tendency in much of the recent philosophical literature has been to assume that there is a substantial continuity between the sorts of explanations found in science and at least some forms of explanation found in more ordinary non-scientific contexts, with the latter embodying in a more or less inchoate way features that are present in a more detailed, precise, rigorous etc.

It is further assumed that it is the task of a theory of explanation to capture what is common to both scientific and at least some more ordinary forms of explanation. These assumptions help to explain what may otherwise strike the reader as curious why, as this entry will illustrate, discussions of scientific explanation so often move back and forth between examples drawn from bona-fide science e.

With respect to the second contrast, most models of explanation assume that it is possible for a set of claims to be true, accurate, supported by evidence, and so on and yet unexplanatory at least of anything that the typical explanation-seeker is likely to want explained. For example, all of the accounts of scientific explanation described below would agree that an account of the appearance of a particular species of bird of the sort found in a bird guidebook is, however accurate, not an explanation of anything of interest to biologists e.

However, different models of explanation provide different accounts of what the contrast between the explanatory and merely descriptive consists in. A related point is that while most theorists of scientific explanation have proposed models that are intended to cover at least some cases of explanation that we would not think of as part of science, they have nonetheless assumed some implicit restriction on the kinds of explanation they have sought to reconstruct.

As we shall see, these empiricist standards and an accompanying unwillingness to employ modal concepts as primitives have continued to play a central role in the models of explanation developed subsequent to the DN model. There are many interesting historical questions about the DN model that remain largely unexplored.

Accuracy of Fossils and Dating Methods

So, how do we know how old a fossil is? There are two main methods determining a fossils age, relative dating and absolute dating. Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages. Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it. Relative Dating The majority of the time fossils are dated using relative dating techniques.

Using relative dating the fossil is compared to something for which an age is already known.

Dating refers to the archaeological tool to date artefacts and sites, and to properly construct history. All methods can be classified into two basic categories: a) Relative dating methods: Based on a discipline of geology called stratigraphy, rock layers are used to decipher the sequence of historical geological events. Relative techniques can determine the sequence of events but not the precise date of an event, .

Renaissance Now, let’s look at some specific examples. One type of atom that does not normally react is Neon. See the picture to the left. It already has the correct number of electrons in it’s outside electron layer so Neon does not react. Neon, along with Helium and Argon are known as non-reacting gasses because they do not need to react to be stable. Other types of atoms such as Hydrogen, Carbon, and Oxygen do not have the correct number of electrons to be stable by itself. Instead they have to share electrons in molecules to get the correct number of electrons in their outside electron layer.

Since we only have to look at the atom that is in the center of the molecule to find out it’s shape, we will concentrate only on Carbon and Oxygen. All the molecules illustrated on this page either have a Carbon or an Oxygen as the center atom. Carbon will especially be of interest since Carbon is the center atom for all the different Amino Acids.

Both Carbon and Oxygen have a deficiency. Neither C nor O have the proper number of electrons in their outside electron layer. Because of that, they are not stable by themselves.

How Does Radiocarbon Dating Work? – Instant Egghead #28


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