IB Biology/Option D - Evolution - Wikibooks, open books for an open world
Jun 1, Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand. Layers of rock build one atop. He was employed at Caltech's Division of Geological & Planetary Sciences at the Examples of Dating Methods for Igneous Rocks Figure 1. The rate of loss of sand from from the top of an hourglass compared to .. This is also true of a number of other igneous rock dating methods, as we will describe below. Figure 3. Which definition, what one. Which of these do you want. Lyngby, Copenhagen, Denmark. D 3 1 outline the method for dating rocks using radioactive isotopes.
In the century since then the techniques have been greatly improved and expanded. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s.
It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization. On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams.
Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event.
This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample. Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1.
Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples. Closure temperatures are so high that they are not a concern.
Radiometric dating - Wikipedia
Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Uranium—thorium dating method[ edit ] Main article: Uranium—thorium dating A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years.
It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured. The scheme has a range of several hundred thousand years. A related method is ionium—thorium datingwhich measures the ratio of ionium thorium to thorium in ocean sediment. Radiocarbon dating method[ edit ] Main article: Carbon is a radioactive isotope of carbon, with a half-life of 5, years,   which is very short compared with the above isotopes and decays into nitrogen.
Carbon, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon ends up as a trace component in atmospheric carbon dioxide CO2. A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesisand animals acquire it from consumption of plants and other animals.
When an organism dies, it ceases to take in new carbon, and the existing isotope decays with a characteristic half-life years. The proportion of carbon left when the remains of the organism are examined provides an indication of the time elapsed since its death. This makes carbon an ideal dating method to date the age of bones or the remains of an organism. It operates based on well understood processes and laws of nature that have not been contradicted by any current observations, and thus is the preferred theory.
The two northern continents are only separated by a small sea, the Bering Straight which has been crossable at times in the past. They have very similar mammal life. The three southern continents have been far more isolated from one another and show far greater variety of mammal life.
Looking at the way in which continents have drifted over time and examining the fossils in them we can map out the development of different sorts of mammals. Monotremes and marsupials developed in Gondwanaland mya before the three southern continents were separated. Placental mammals developed life young developed later mya and replaced almost all of the monotremes egg laying mammals and marsupials undeveloped young born into pouches in the other continents.
Australia was separated from the other continents so animals there could no longer mate with animals from other continents and Australian animals could not travel elsewhere. This is why marsupials and monotremes are now found only on Australia. Monotremes and marsupials have evolved to fit the niches within the Australian environment and there are no placental mammals. This is simply because of geography not because Australia is unfit for placental mammals.
These observations and other similar examples are expected under the theory of evolution. Study of past evolution - phylogeny Sand eroded from the land is first carried by rivers, seas, swamps where the particles settle to the bottom.
These deposits pile up and compress the older sediments into rock. Dead organisms are swept into seas and swamps then settle to the bottom with the sediments.
When the sediments turn to rock under pressure the hard parts of the animal may remain as fossils. Minerals also leach into the soft parts of the organism, leaving a petrified cast of its shape within the rock.
Fossils can also be stored in: Resins, which become amber Frozen in ice or snow In acid peat in which they cannot decay D. Fossils contain isotopes of elements that accumulated in the living organisms.
If the isotopes are unstable, they will lose protons and break down over time. Since each radioactive isotope has a fixed half-life it can be used to date fossils based on the relative concentrations of the reactant and product of the decay. Half life is the amount of time it takes for half of a sample of a certain substance to break down.
Everything Worth Knowing About Scientific Dating Methods | cidadessustentaveis.info
Carbon has a half life of years so useful or dating fossils less thanyears old. Potassium has a half-life of 1. Look on the graph at how many times the concentration of the original isotope has halved then multiply that by the half-life. The existence of the many fossils similar but different to current species is expected under evolution.
The Acanthostega fossil shows an amphibian from mya which has eight fingers and seven toes so is different from current organisms. It has four legs and a backbone like mammals, reptiles and amphibians but also a fish like tail and gills.
It lived in water. In the horse, the number of toes they have has been reduced from four to one. A succession of fossils from the horse ancestor with four toes to a modern horse with one toe shows a trend towards reduced number of toes. A clear progression of species is visible in the fossil record over time, from bacteria, to simple water based organisms, to amphibians, to insects, to reptiles and finally to mammals.
All living organisms have DNA, use the same 20 amino acids and use left, not right handed amino acids. This suggests that all life forms had a common ancestor which did the same. To determine further relationships between organisms, comparing DNA and protein structure can be helpful.
The tighter the bond the greater the similarity and the more closely related the species. Most fundamental enzymes present in most living creatures have a similar amino acid structure. Proteins are genetically determined. Thus a close match in the amino acid sequence of two proteins from different species indicates that the genes in those proteins evolved from a common gene present in a shared ancestor.
Mutations are random changes in gene structure but they occur at a roughly predictable rate.
D 3 1 outline the method for dating rocks using radioactive isotopes
In general the more differences between the amino acid sequence of a common protein, the further in the past two species had a common ancestor.
For example, the haemoglobin of gorillas only differs by one amino acid from human haemoglobin whereas elephant haemoglobin differs from human haemoglobin by 26 amino acids. Therefore elephants separated as a species from a common ancestor with humans longer ago then did gorillas. Information like this can help to group organisms in trees of descent and suggest how long ago they had a common gene pool.
Scientific Dating Methods This dating scene is dead. The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results. Sometimes only one method is possible, reducing the confidence researchers have in the results.
Methods fall into one of two categories: These methods — some of which are still used today — provide only an approximate spot within a previously established sequence: Think of it as ordering rather than dating. One of the first and most basic scientific dating methods is also one of the easiest to understand. Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.
A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species. The polarity is recorded by the orientation of magnetic crystals in specific kinds of rock, and researchers have established a timeline of normal and reversed periods of polarity. Paleomagnetism is often used as a rough check of results from another dating method.
Within hours or days of a volcanic eruption, tephra — fragments of rock and other material hurled into the atmosphere by the event — is deposited in a single layer with a unique geochemical fingerprint. Researchers can first apply an absolute dating method to the layer.
They then use that absolute date to establish a relative age for fossils and artifacts in relation to that layer.