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Radiation-damage dating, method of age determination that makes use of the damage to crystals and the radiation from radioactive substances caused by storage of energy in electron traps. In the mineral zircon, for example, radiation damage results in a change in colour, the storage of energy in electron traps, and a change in the crystallographic constants of the mineral. Cosmic ray definition, a radiation of high penetrating power that originates in outer space and consists partly of high-energy atomic nuclei. See more. Radiometric dating is a means of determining the "age" of a mineral specimen by determining the relative amounts present of certain radioactive elements. By "age" we mean the elapsed time from when the mineral specimen was formed. Radioactive elements "decay" (that is, .

Try refreshing the page, or contact customer support. Register to view this lesson Are you a student or a teacher? I am a student I am a teacher. Try Study. Cancel anytime. What teachers are saying about Study. Coming up next: Theories of Evolution: Lamarck vs. Just checking in. Are you still watching? Keep playing. Your next lesson will play in 10 seconds. Save Save Save. Want to watch this again later? Create an account. Principles of Radiometric Dating.

What is Relative Dating? What is Relative Age? Relative vs. Absolute Time in Geology. What is Carbon Dating? Alfred Wegener's Theory of Continental Drift.

High School Biology: Help and Review. College Biology: Help and Review. Lesson Transcript. Discover how scientists determine the age of fossils, rocks, and other geologic phenomena by using the known half-lives of isotopes within each specimen, a technique known as radioactive dating.

Radioactive Dating Ever wonder how scientists concluded the age of the earth to be about 4. Radioactivity Defined Elements occur naturally in the earth, and they can tell us a lot about its past. The Half-Life Isotopes decay at a constant rate known as the half-life. Try it risk-free No obligation, cancel anytime. Want to learn more? Radiocarbon Dating Since all living things contain carbon, carbon is a common radioisotope used primarily to date items that were once living.

Lesson Summary So, to sum this all up, radioactive dating is the process scientists use to conclude the ages of substances dating back several to many years ago by using the isotopes of elements and their half-lives. Unlock Your Education See for yourself why 30 million people use Study. Become a Member Already a member? Earning Credit. Earning College Credit Did you know We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities.

To learn more, visit our Earning Credit Page Transferring credit to the school of your choice Not sure what college you want to attend yet? Browse Articles By Category Browse an area of study or degree level. Area of Study. Degree Level. You are viewing lesson Lesson 9 in chapter 20 of the course:. Science Basics: Tutoring Basic Science Lab Skills Inorganic Chemistry Review for In both cases, we could retrieve the tree probabilities Fig. Extensive simulations were used to validate the MCMC algorithms.

Here we show a simple example: retrieval of the uniform clock tree prior for a tree with four extant taxa a and c and a tree with two extant taxa and two extinct taxa b and d. The age of the tree root was fixed to 1.

Radioactive dating enables geologists to record the history of the earth and its events, such as the dinosaur era, within what they call the geologic time scale. Radioactive dating uses the ratios. Jul 26,   Here, we contrast such node dating with an approach that includes fossils along with the extant taxa in a Bayesian total-evidence analysis. As a test case, we focus on the early radiation of the Hymenoptera, mostly documented by poorly preserved impression fossils that are Cited by: Start studying Radioactive Dating. Learn vocabulary, terms, and more with flashcards, games, and other study tools.5/5(5).

Both tree probabilities a and c and branch length distributions b and d; only part shown in d closely match analytically derived values.

The results shown are for the strict-clock model; similar results were obtained under all relaxed-clock models. To generate samples from the posteriors, we used four independent runs of four parallel chains each MrBayes command blocks for all analyses are provided as Supplementary Material. The initial heating coefficient was set to 0.

We used random starting trees, and sampled parameters and trees every generations. Convergence was assessed by the built-in diagnostics of MrBayes 3. We also examined trace plots of likelihoods, chain swap frequencies, and parameter samples for evidence of non-stationarity or poor mixing. The diagnostic criteria were met for all parameters in all analyses except as noted below for the CPP model. Bayes factors were used to choose among relaxed-clock models.

They were calculated from estimates of the marginal likelihoods obtained using the stepping stone sampling approach Xie et al. Our implementation estimates model likelihood by going from posterior to prior or in the reverse direction.

It supports multiple-run convergence diagnostics, implements both initial and stepwise burn-in, and uses Metropolis coupling to enhance mixing during the entire procedure. The consensus tree obtained in an initial nonclock analysis of the combined extant data set Fig. Most of the basal nodes received maximal support from the combined data set, posterior probability PP of 1.

Regions of uncertain resolution mainly include Tenthredinidae and Apocrita; the latter was very sparsely sampled. Additionally, the relationships at the base of Unicalcarida remain uncertain, especially whether Xiphydria is the sister to Vespina or to Siricidae. The nonclock tree also shows that the rate of molecular evolution varies considerably between hymenopteran lineages, most conspicuously exemplified by the very short branches leading to extant Xyeloidea Fig.

The Xyeloidea form the sister group of all other extant Hymenoptera in our analysis; previous studies have always placed the two constituent lineages, the Xyelinae and Macroxyelinae, at the very base of the hymenopteran tree, but variously as: a monophyletic group Schulmeister ; Vilhelmsen ; as two separate lineages, each being the sister group of a large clade of other hymenopterans Rasnitsyn ; as a basal grade with other hymenopterans monophyletic Ronquist et al.

The Xyeloidea have apparently retained many primitive characters found in the oldest known hymenopteran fossils Rasnitsyn Our results show that the Xyeloidea are characterized by low evolutionary rates both in morphological and molecular characters. The choice of clock model and rooting method had a large impact on tree topology Fig.

The nonclock topology Fig. Imposing a strict clock drastically changed the topology, most importantly by shuffling the outgroups and rerooting the hymenopteran tree on the branch separating the Vespina from other hymenopterans Fig.

Constraining the Holometabola to be monophyletic, to help structure outgroups according to the received wisdom, did not reverse the unorthodox rooting of the hymenopteran tree Fig. Unconstrained relaxed-clock models similarly resulted in an unorthodox topology Fig. All subsequent analyses used relaxed-clock models with the Holometabola constrained to be monophyletic. Clock model and rooting assumption had a large effect on tree topology.

When a clock was not assumed, the morphological amolecular not shownand combined morphological and molecular b trees were virtually congruent and agreed well with previous studies.

The widths of clades are proportional to their representation in our data set, not to their true diversity. Only extant taxa were included in the analyses shown here. To select the best relaxed-clock model, we performed Bayes factor comparisons. Because the dating approach could influence the results, we performed the comparisons separately on the uncalibrated, node-calibrated, and total-evidence-calibrated data sets.

Model likelihoods were computed using the stepping-stone algorithm Xie et al. Four independent analyses were performed on each data set. The results differed across data sets. For the total-evidence data set, we had some difficulties with convergence among the four independent stepping-stone analyses.

A Total-Evidence Approach to Dating with Fossils, Applied to the Early Radiation of the Hymenoptera

The scatter among estimates was about 10 to 15 log likelihood units except for TK02, see belowwhereas it was around 5 log likelihood units for the other data sets. However, the results do suggest that inclusion of the fossils changed the performance of the models. Examining the uncalibrated trees estimated by the different relaxed-clock models Fig.

The IGR model allows the changes in substitution rates on adjacent basal branches to be quite extreme, accounting for most of the rate variation in the whole tree Fig.

In some cases, rates are strongly decelerated on one branch and accelerated on its sister branch, for example, in the most basal xyelid branch and in the ancestor of all other Hymenoptera. The autocorrelated CPP and TK02 models have a smoothing effect, such that the rate changes occur more slowly and over a larger part of the basal tree Fig.

The result is that the time duration of many basal branches is extended. For the uncalibrated analyses in general, the choice of relaxed-clock model had only a small effect on the estimates of effective branch lengths but often a profound effect on the estimated time lengths of the branches Fig. Different relaxed-clock models result in different relative divergence time estimates uncalibrated trees. The letters denote the branches examined in plots c-f, respectively. For the relaxed-clock models, we plotted both the time length in expected substitutions per site at the base rate of the clock and the corresponding effective branch length, which equals the time length times the rate estimated for that branch see labels in Fig.

Note that effective branch lengths tend to be very similar to nonclock branch lengths, while time length distributions vary more across relaxed-clock models and tend to be less precise.

In the dated analyses, the extension of the basal branches resulted in the autocorrelated models implying the existence of considerably longer, unsampled ghost lineages than the IGR model, suggesting that the IGR model fits the fossil record better. Despite the fact that our tree model did not account for fossil sampling and thus did not penalize long ghost lineages, inclusion of the fossils in the analysis nevertheless tipped the model comparison in favor of the IGR model, as mentioned above, giving additional support for the idea that the IGR model agrees better with the fossil data.

For these reasons, and because it also appears to us that it is more important to capture the apparently drastic rate changes among basal hymenopteran branches than it is to exactly model the rate autocorrelation in the rest of the tree, we focus on the IGR results in the following.

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Presumably, the rate variation in our data set would have been described more accurately by a relaxed-clock model allowing the degree of rate autocorrelation to change across the tree, unlike the models we explored. When fossils were included as terminals in the total-evidence analysis, the consensus tree was highly unresolved Fig.

The fossils that jump around in the tree mask any potential resolution among extant taxa in the consensus tree. When the consensus tree was calculated from the same tree sample after the fossil taxa were removed, the relationships among extant taxa were highly resolved and corresponded to the relationships obtained when analyzing extant taxa alone.

Majority-rule consensus tree from a total-evidence analysis including all fossils IGR model. The tree is poorly resolved, which reflects the uncertainty in fossil placement. The underlying consensus tree of extant taxa is virtually identical to trees obtained in analyses without fossils see Figs. Grey-scale boxes indicate the percentage of morphological characters that were coded for each taxon, showing the incompleteness of the fossils.

Values above branches represent PPs. The uncertainty concerning the phylogenetic placement varied considerably among the fossils. While some of the better preserved fossils could be assigned with high PP to a specific branch of the tree of extant taxa e. In some cases, this was apparently due to poor preservation e.

Dating radiation

The uncertainty in phylogenetic placement varied considerably across fossils. We show the PPs of four example fossils attaching to specific branches on the majority rule consensus tree of the extant taxa IGR model. Figure 9 shows the dated phylogeny obtained in the total-evidence analysis, with error bars on node ages from both total-evidence and traditional node dating. When comparing the age estimates, it is striking that all nodes outside Hymenoptera and in Xyelidae are estimated to be younger under the total-evidence approach, whereas the opposite is true for nodes within Hymenoptera excluding Xyelidae arrows in Fig.

Furthermore, the variance of each estimate can differ considerably between the two approaches, usually being smaller in total-evidence dating e. A striking exception is the age of the Xyelidae, where node dating leads to a much narrower but probably erroneous; see below age estimate.

Comparison of node age estimates obtained using total-evidence dating red in the online version, light gray in the print version node dating blue in the online version, dark gray in the print version under the IGR model. Two nodes in the Apocrita clade lower part of tree were differently resolved in the node-dating analysis, and the blue bars are therefore missing for these.

Arrows indicate the direction and extent to which the median node age shifted from the total-evidence analysis to the node-calibration analysis. Posteriors obtained under node dating and total-evidence dating are compared across three different priors on tree age for eight nodes a-h; cf. Table 2. The nodes correspond to the most recent common ancestor of the extant forms of the specified taxa. For the intermediate prior on tree age, we used an offset-exponential distribution with a minimum of Ma oldest neopteran fossil and a mean of Ma oldest insect fossil.

For the more and less restrictive prior, we shifted the mean to half and twice the distance to the minimum Ma and Marespectively.

Note that the total-evidence posteriors are less sensitive to prior assumptions than node-dating posteriors. They also tend to be more precise; if not, the total-evidence analysis indicated that the calibration points were based on erroneous or doubtful assumptions about fossil placement, causing posteriors to be artificially truncated c; probably also e and f.

To study the precision and robustness of the age estimates, we varied the offset exponential prior distribution on the root age of the tree by doubling or halving its mean. This comparison shows that the total-ev idence approach is less sensitive to prior choice than the node-calibration approach Fig. The posterior also tends to be more precise. The exceptions Fig. A prominent example is the Xyelidae calibration, mentioned above, which was based on the fossil Eoxyela tugnuica.

This conflict in the placement of the calibration-point fossil is reflected in the node-dating analysis by an artificially narrow posterior distribution on the Xyelidae age, pushed towards the minimum age constraint Fig. In many ways, relaxed-clock models are intermediate between strict-clock and nonclock models Drummond et al. For instance, relaxed-clock models use much fewer parameters roughly half as many as nonclock models, but slightly more parameters than strict-clock models.

They account for rate variation across lineages, unlike strict-clock models, but not as well as nonclock models. They provide weaker signal on the position of the root than strict-clock models, but stronger than nonclock models, which convey no rooting information at all. In theory, relaxed-clock models could provide more precise and accurate phylogenetic results than either the strict-clock or nonclock models if they strike a better balance between model complexity number of parameters and model adequacy accommodating rate variation across lineages Drummond et al.

However, a recent simulation study has shown that this might not always be the case in practice Wertheim et al. As expected, we observed topological artifacts under the strict-clock model, but most of these artifacts remained under the relaxed-clock models Fig.

These topological artifacts would presumably have disappeared if the rate smoothing effect of the relaxed-clock priors had been decreased. However, this would have removed much of the information about the position of the root and the time length of the branches, making it very challenging to date the tree. Because most of the rate variation in our data set was due to a few major rate changes, such an approach would probably also have resulted in exaggerated uncertainty in the dating of the bulk of the tree.

Rather than over-relaxing the clock, we chose to introduce a topological constraint close to the root of the tree to provide additional rooting information.

Our results show that such a rooting constraint, on its own, can help relaxed-clock models pinpoint relevant rate changes close to the root and correct topological artifacts. The fact that the Holometabola constraint alone is sufficient to make all relaxed-clock models retrieve the expected topology Fig.

Of course, rooting constraints introduced in relaxed-clock analyses should be well justified.

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Few entomologists are likely to doubt the monophyly of Holometabola, which is supported by a large body of ontogenetic, ecological, and molecular evidence Beutel et al. It has been pointed out in the literature that both strict and relaxed-clock models could, in principle, be used to root phylogenetic trees without introducing outgroup constraints Huelsenbeck et al. However, such rooting can be misled by model misfit, especially for strict-clock models Huelsenbeck et al.

Our results demonstrate several of these problems and exemplify the strength of the outgroup rooting method, even in the context of relaxed-clock models. It is interesting to note that, despite their superficial similarity, there are clear differences among the three relaxed-clock models we explored in the estimated time tree. Even more interesting is the fact that their adequacy, as evidenced by Bayes factor comparisons, is influenced by the inclusion of fossils.

Radioactive dating. Radioactive dating is helpful for figuring out the age of ancient things. Carbon (C), a radioactive isotope of carbon, is produced in the upper atmosphere by cosmic radiation. The primary carbon-containing compound in the atmosphere is carbon dioxide, and a very small amount of carbon dioxide contains C Learn about different types of radiometric dating, such as carbon dating. Understand how decay and half life work to enable radiometric dating. Play a game that tests your ability to match the percentage of the dating element that remains to the age of the object. Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events.

Apparently, it is the presence of a few major rate changes close to the root of the hymenopteran tree that causes the major differences between the estimated time trees. As far as we can judge, this part of the tree is modeled best by the uncorrelated IGR model, which allows drastic rate variation among adjacent branches, whereas the autocorrelated CPP and TK02 models do better in the rest of the tree, where there is significant rate autocorrelation.

Without fossils, the overall rate autocorrelation seems to determine the outcome of the model comparison, whereas inclusion of the fossils puts more emphasis on model adequacy in the basal part of the tree.

An observation that seems to support these conclusions is that the CPP model performs better than the TK02 model across all data sets. In the CPP model, rate multipliers are thrown onto the tree according to a Poisson process. Although this is an autocorrelated model, it takes only one extreme multiplier, or a combination of a few multipliers, to generate more abrupt changes in evolutionary rate than would be expected in the gradual, continuous TK02 model of rate variation.

In total-evidence dating, the phylogenetic position of a fossil and the time duration of the branch connecting it to the extant tree are determined based on morphological evidence.

The more similar a fossil is to the inferred morphology of an ancestor in the extant tree, and the more complete it is, the more it will influence the dating of the extant tree. In fact, however, all dating using fossils is based to some extent on the assumption that morphological similarity indicates temporal proximity. Even the most ardent opponents of the idea would have to agree that the fundamental assumption of morphological phylogenetic inference, descent with modification, implies that there is some correlation between morphological change and time.

Of course, the rate of the morphological clock is likely to vary considerably over time and over characters cf. Supplementary Figure 1and there are likely to be complex dependencies between the evolutionary rates of different morphological characters.

Nevertheless, we argue that it is better to attempt to explicitly quantify the morphological clock evidence, even if based on incomplete and over-simplified models of morphological evolution, than it is to use the evidence implicitly in constructing probability distributions for the age of calibration nodes. An interesting question is whether the variation in evolutionary rates across the tree should be modeled jointly or separately for morphological and molecular data Pyron We chose to model the rate variation jointly for several reasons.

First, nonclock analyses showed that rate variation across the tree was clearly correlated across morphological and molecular partitions see Supplementary Material.

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This was particularly obvious in the Xyeloidea, a clade that was characterized by extremely slow rates of both morphological and molecular evolution, but it appeared in many other parts of the tree as well. Second, our MCMC sampling was over effective branch lengths, and there would have been twice as many effective branch lengths about additional parameters to sample over if rate variation had been modeled separately for morphology and molecules.

We suspected it would be difficult to obtain convergence over such a large parameter space see also Pyron Finally, modeling the rate variation separately could possibly also have resulted in problems related to over-parameterization. Nonetheless, we consider it worthwhile to further explore the separate modeling approach, especially for problems with fairly complete fossils and extensive morphological data.

Another concern under total-evidence dating is the impact of missing data. Ambiguous data entries are inevitably numerous for fossil taxa, which usually cannot be scored for any of the molecular characters. Especially when non-randomly distributed among taxa, such missing entries in the data matrix can interact with priors on topology and branch lengths in a way that could mislead tree reconstruction and divergence time estimation Lemmon et al.

On the other hand, such detrimental effects of missing data are probably weaker in the presence of a strong phylogenetic signal, and thus might have little impact when there is enough decisive data available Lemmon et al. In our analyses, the addition of fossils had little impact on the topology recovered for extant taxa, suggesting that inferred relationships are not affected by missing data.

But missing data could still affect branch length estimates, which are crucial for dating analyses. If so, then the least complete fossils should cause the most severe bias in estimated divergence times. As expected, the confidence intervals of the divergence time estimates obtained with the reduced fossil set were usually wider, especially for those clades from which many fossils had been removed.

This indicates that possible spurious effects caused by additional missing-data entries in the matrix are outweighed in our total-evidence dating analysis by the positive effects resulting from additional temporal information added by each fossil, however incompletely preserved. From a theoretical standpoint, total-evidence dating is preferable over standard node dating simply because it explicitly incorporates the fossil information instead of relying on secondary interpretation.

We might also expect total-evidence dating to make more efficient use of the available data. The ideal case would be the dating of trees with poorly preserved fossils of uncertain affinity, which are difficult to use in node dating.

However, such fossils might contain so little dating information that there is nevertheless little to gain from a total-evidence analysis. Our results confirm that it is difficult to use the node-dating approach for hymenopteran dating because of the uncertainty in the placement of most fossils Fig. This is not surprising given the incompleteness of many of the fossil specimens, such as the single forewing remaining of Sogutia liassica Fig.

Despite these difficulties, however, the fossils contribute significantly to the dating of the tree in the total-evidence analysis.

Compared to the node-calibration approach, the posterior distributions on divergence times are less sensitive to prior assumptions and also tend to be more precise in the total-evidence analysis Fig. Arguably, they also agree better with other dating studies, as discussed in detail below. Perhaps more importantly, the total-evidence analysis highlighted several problems in the node-dating analysis. It showed that the PP of the critical fossil actually attaching in the predicted place on the extant tree was very low for no less than four of the seven Hymenoptera calibration points Table 3.

Such erroneous or biased node calibrations can lead to various problems in the inferred dates. For instance, the Xyelidae are estimated to be much older in the node-dating analysis than in the total-evidence analysis because the former assumes that the fossil Eoxyela tugnuica is positioned inside the Xyelidae.

The conflict between the hard lower bound on the age calibration of the Xyelidae and the branch length information from the phylogenetic model causes the posterior distribution on the xyelid age to be exceedingly narrow in the node-calibration analysis, pushed hard against the minimum age constraint.

Some of these artifacts can be avoided by using soft instead of hard bounds on the calibration ages Yang and Rannala However, this assumes that it is possible to appropriately accommodate phylogenetic uncertainty in the calibration distributions, which appears more difficult to us than to actually incorporate the fossils in a total-evidence analysis.

Alternative approaches to reconcile conflicting calibration points include compatibility and cross-validation analyses Near et al. However, these approaches tend to discard incompatible calibration points without considering the evidence supporting each one of them.

In this and many other respects, they represent less powerful approaches than a true total-evidence analysis. An interesting phenomenon is that our total-evidence analysis dated most nodes outside the Hymenoptera as younger, and most nodes inside the Hymenoptera as older, than the node-calibration analysis Fig.

It is not entirely clear why, but it could partly be due to our tendency to place fossils inside extant groups, such as families, instead of fully considering the possibility that they belong to stem lineages further down in the tree. If so, this would help pull deep nodes towards the recent in the total-evidence analysis, where fossils find their position based on the available character evidence instead of on our ability to classify them correctly.

However, it cannot explain why most Hymenoptera nodes are assigned older dates in the total-evidence analysis. This could possible be related to differences in the priors used for node dating and total-evidence dating. This is considerably older than most previous estimates, which placed the origin in the Triassic e. In fact, our age estimate might seem unrealistically high given the known fossil record. For instance, it leaves a 74 myr gap to the first occurrence of Hymenoptera in the fossil record Triassoxyela foveolata and Leioxyela antiqua at Ma; Rasnitsyn ; Rasnitsyn and Quicke Furthermore, while our dating analysis places the major radiation of basal Hymenoptera in the Permian, most higher hymenopteran groups, including the Apocrita, are recorded for the first time only from the Lower Jurassic Rasnitsyn The rather numerous hymenopteran fossils from the Triassic are currently all attributed to the Xyelidae Rasnitsyn and Quicke, Several factors could result in a bias toward too deep divergence times in our analyses.

In the node-dating analysis, incompatible calibration points could lead to too deep splits Benton and Ayalaand the same holds true for inappropriate modeling of morphological characters and possibly for the uniform tree prior in the total-evidence approach. Whether any of these mechanisms biased our results remains to be shown.

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However, other lines of evidence suggest that our estimate might not be that unrealistic after all. First, the scarcity of hymenopteran fossils, especially in the early Jurassic, indicates that the order may be considerably older than the oldest fossils. Considering that the second oldest fossil at Ma Sogutia liassica ; Rasnitsyn is separated by 45 myr from the oldest fossils, a gap of 74 myr between the oldest fossils and the origin of the order seems at least possible.

Such major gaps in the fossil record are rather the rule than the exception in arthropods due to factors such as poor preservation, small size, limited distributional ranges, and a lack of attention from paleontologists Wills In fact, even the best current fit of a Hymenoptera phylogeny to the fossil record contains a number of gaps in the range myr Rasnitsyn Furthermore, it is possible that the preponderance of xyelid fossils in the Triassic is due to the fact that other hymenopterans were less diverse and abundant during this time period.

Another possibility is that some of the Triassic xyelids are actually unrecognized members of other basal hymenopteran lineages. Accumulating evidence suggests that the Hymenoptera are the sister group of all other holometabolan insects Beutel et al.

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If so, and if hymenopterans radiated into extant lineages soon after their origin as suggested by our tree, then the age of the Hymenoptera should be close to the age of the Holometabola. The fossil record of several other holometabolous orders extends well into the Permian Grimaldi and Engelsuggesting that the Hymenoptera are at least this old. It could represent a hymenopterous gall, but this interpretation is rather controversial Grimaldi and Engel ; Labandeira and Phillips There is abundant additional evidence suggesting that the stem lineage of hymenopterans had separated from other Holometabola by the late Carboniferous Rasnitsyn, ; Rasnitsyn et al.

It is here that our results differ by suggesting that the hymenopteran radiation started earlier, soon after the split from other holometabolans, leaving little room for a Palaeomanteida-like stem group.

It should be borne in mind, however, that we did not include representatives of early holometabolans, such as the Palaeomanteida, in our study. A total-evidence analysis sampling more broadly across extant and extinct holometabolan lineages is needed before firm conclusions can be drawn on the time duration of the hymenopteran stem lineage and the role of the Palaeomanteida in the emergence of modern hymenopterans.

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Regardless of the conclusion on the fit to the early hymenopteran fossil record, our results do agree well with a number of other dating studies. For instance, a recent supertree analysis Davis et al. Age estimates for Hymenoptera based on molecular data are rather scarce. Wiegmann et al.

Other hymenopteran dating studies suggest that ants are at least myr Moreau ; Moreau et al. We conclude that, when feasible, total-evidence dating should be preferred over node dating. This is not only because total-evidence dating directly incorporates the evidence on which fossil dating is based instead of relying on indirect methods that may obscure or misrepresent the available data. Our study shows that total-evidence dating can also clearly outperform node dating when extracting information from poorly preserved fossils.

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Moreover, the total-evidence approach provides a much better platform for future development of fossil dating. For instance, we can now start to directly explore models of speciation, extinction, sampling, and fossilization, and their effect on fossil dating of phylogenies, as a natural component of total-evidence analyses e.

From Wikipedia, the free encyclopedia. Redirected from Radioactive dating. A technique used to date materials such as rocks or carbon. See also: Radioactive decay law. Main article: Closure temperature. Main article: Uranium-lead dating. Main article: Samarium-neodymium dating. Main article: Potassium-argon dating.

Main article: Rubidium-strontium dating. Main article: Uranium-thorium dating. Main article: Radiocarbon dating. Main article: fission track dating. Main article: Luminescence dating. Earth sciences portal Geophysics portal Physics portal. Part II. The disintegration products of uranium".

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