K–T boundary

Detection of a new form of carbon in volcanic rock samples from Anjar town in Gujarat in western India has revived the debate on what killed the dinosaurs. Dinosaurs and almost 80 per cent of Earth’s other organisms were wiped out 65 million ears ago at the so-called K-T boundary KTB that marks the end of Cretaceous K , and beginning of Tertiary T periods in the geological calendar. Some say it was the result of extraterrestrial objects hitting the earth, a theory originally proposed by the Nobel physicist Luis Alvarez. Others blame it on vast clouds of climate-altering gases released by eruptions that buried western India under layer upon layer of basaltic lava flows nearly 3, meters thick. Now, researchers from India’s three national laboratories have joined the fray. They report that their discovery of a new phase of fullerene or Carbon in the Anjar sedimentary rocks bolsters the impact theory. According to this theory, a meteorite the size of a small city that landed in Chicxulub in Mexico 65 million years ago, coinciding with KTB, kicked up so much dust that it caused a global blackout triggering mass extinction. The key evidence of impact, besides the crater, is the abnormally high concentration of element Iridium found at K—T boundaries across the world.

A dating success story: genomes and fossils converge on placental mammal origins

Metrics details. The timing of the placental mammal radiation has been a source of contention for decades. The fossil record of mammals extends over million years, but no confirmed placental mammal fossils are known prior to 64 million years ago, which is approximately 1. Thus, it came as a great surprise when the first published molecular clock studies suggested that placental mammals originated instead far back in the Cretaceous, in some cases doubling divergence estimates based on fossils.

In the last few decades, more than a hundred new genera of Mesozoic mammals have been discovered, and molecular divergence studies have grown from simple clock-like models applied to a few genes to sophisticated analyses of entire genomes.

As a result, recent scientific papers refer to the K-T boundary as the K-Pg boundary. Dating the K-T Boundary. The date of the K-T (or K-Pg) boundary has also.

Skip to main content Skip to table of contents. This service is more advanced with JavaScript available. Encyclopedia of Paleoclimatology and Ancient Environments Edition. Contents Search. How to cite. The end result is a crater tens to hundreds of kilometers in size. Although the existence of large impact structures on Earth is undisputed, the possible climatic effects of an impact were not seriously considered until , when a team led by the famous physicist Luis Alvarez and his son, the geologist Walter Alvarez, suggested that the profound end-Cretaceous mass extinction might have been caused by the impact of a km diameter asteroid or comet Alvarez et al.

Dated to 65 million years ago, this extinction is the last of the large, known mass extinctions on Earth and defines a major geologic boundary between the Cretaceous and Tertiary or Paleogene, as

RE: Precise K-T boundary dating

A number of radiometric methods of dating rocks are used by Geologists. These techniques rely on measuring the rate of decay of certain isotopes contained with rock and mineral samples. As certain isotopes are known to decay at a constant rate, measuring the levels and ratios of isotopes within a rock sample can provide evidence of how old the rock is. One of the most common methods used is the argon-argon dating method. It can be used to date rocks that are millions or even billions of years old.

This dating method is particularly suitable for dating volcanic materials igneous rocks.

The KT boundary and mass extinction was first discovered based on planktic foraminifera from volcanic eruptions based on 40K/40Ar and 40Ar/39Ar dating.

All rights reserved. New insights about the asteroid thought to have killed off the dinosaurs suggest it may have just been the final blow, and that the reptiles were already suffering from a finicky climate prompted by volcanic eruptions long before the meteorite struck. The research, detailed in the February 8 issue of the journal Science , adds to the ongoing scientific debate over what exactly killed off the dinosaurs.

That debate, which once revolved around the question of whether the culprit was an asteroid or volcano-induced climate changes, has evolved to consider the possibility that perhaps multiple environmental factors were involved. Using a high-precision dating technique on tektites—pebble-sized rocks formed during meteorite impacts—from Haiti that were created during the event, the team concluded that the impact occurred 66,, years ago—slightly later than previously thought.

When error limits are taken into account, the new date is the same as the date of the extinction, the team says, making the events simultaneous. Renne said the new findings should lay to rest any remaining doubts about whether an asteroid was a factor in the dinosaurs’ demise. That is not to say, however, that the asteroid—which carved out the so-called Chicxulub crater—was the sole cause of the dinosaurs’ extinction. Evidence now suggests massive volcanic eruptions in India that predated the asteroid strike also played a part, triggering climate changes that were already killing off some dinosaur groups.

For example, “nobody has ever found a non-avian dinosaur fossil exactly at the impact layer,” Renne said in an email. The idea that volcanism was responsible for the dinosaurs’ demise actually predates the impact theory, and it fits well with what is known about Earth’s other mass extinction events. But in the s, father-son team Luis and Walter Alvarez, a physicist and planetary scientist, respectively, presented a bold new theory.

Cretaceous/Tertiary (K-T) Boundary Impact, Climate Effects

Few episodes in geologic history are as widely recognized as the Cretaceous-Paleogene, or K-Pg, boundary 66 million years ago. Mention it to science-interested laymen, meanwhile, and they may conjure images of tyrannosaurs peering over their shoulders in anguish as they flee from streaking meteors. These catastrophic events make for a compelling and, aside from artistic liberties taken in some recountings, mostly truthful tale. Paleontologists have long recognized from the fossil record that more than half of the species inhabiting Earth perished at the end of the Mesozoic — the most emblematic of course being the remaining nonavian dinosaurs, like T.

Possibly totaling more than 1 million cubic kilometers, these lava flows — known as the Deccan Traps — erupted over several million years, beginning before and ending after the mass extinction. The debate over the cause of the K-Pg extinction has continued to simmer through the years, boiling over at times as proponents of each explanation traded barbs in the literature and at scientific meetings.

Collisions of asteroids and comets with the Earth’s surface are rare events that punctuate the geologic record. The collision of a large asteroid or comet with a.

My suggestion is to read through the press releases and summaries first because they are intended for a more general audience. Note the different writing styles and differing amounts of technical jargon in the different papers! I have posted some discussion questions you might want to look at first help guide your thinking, so you are ready to discuss. We will discuss these papers together via a discussion in Canvas.

This discussion will take place over the second week of this lesson. Grading rubric: Please see the rubric for discussions. Skip to main content. The three scientific articles I have selected are intended to walk you through the most recent debate over exactly what killed the dinosaurs and how the timing worked. You will see that there is a set of questions, below, to guide your thinking as you read.

Nature, , Burgess, S. Deciphering mass extinction triggers. Science, ,

Impact or eruptions: Are both to blame in the great end-Cretaceous whodunit?

Plants and the K—T Boundary. Its impact on plant life appears to have been of a much lesser magnitude. The authors, both on the staff of the Denver Museum of Nature and Science, have published extensively on fossil plants of Tertiary and Cretaceous age. Nichols has been mainly concerned with the palynology the microfossil record , while Johnson has concentrated on leaf assemblages megafossils of this age span.

However, the onset of volcanism in the Siberian Traps apparently occurred at a time postdating that of the Permian/Triassic boundary.

Was it a comet or asteroid impact? Volcanic eruptions? Climate change? In an attempt to resolve the issue, an international team of scientists have determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known impact that occurred around the same time. The new extinction date is precise to within 11, years. The revised dates clear up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures.

The new date for the impact — 66,, years ago — is the same within error limits as the date of the extinction, said Renne, making the events simultaneous. Argon-argon dating uses a mass spectrometer to measure the ratio of radioactive potassium in a sample of rock to its decay product, argon. The amount of argon in a sample allows researchers to use rocks as incredibly slow clocks. Many people think precision is just about adding another decimal place to a number, but it’s far more exciting than that.

It’s more like getting a sharper lens on a camera. It allows us to dissect the geological record at greater resolution and piece together the sequence of Earth history.

Refining the date of the K/T boundary and the dinosaur extinction

Ajoy K. Geology ; 19 5 : — A basalt lava flow from the lowermost horizon yields an age of Shibboleth Sign In. OpenAthens Sign In. Institutional Sign In.

Radiometric dating of these formations assigns them to the final million years of the Cretaceous, and paleomagnetic dating narrows the dates.

Indeed, had it not been for the presence of abundant dinosaur remains in the Ojo Alamo Sandstone, its Paleocene age would probably never have been questioned. Because the last occurrence of dinosaur bone has always been considered by vertebrate paleontologists to mark the end of the Cretaceous Period, various explanations were suggested to explain away the presence of these dinosaur remains in what otherwise appeared to be Paleocene rocks.

For a complete discussion of those explanations, see Fassett et al. The relative age of sedimentary rock formations was originally based on the fossils found in those rocks Winchester This criterion worked extremely well for marine rocks containing abundant fossils of small, steadily evolving, mostly invertebrate life forms, but was much less useful for continental strata containing far fewer diagnostic fossils, such as those of vertebrates.

Where present, the last occurrence of dinosaur fossils was traditionally used to mark the top of the Cretaceous and Paleocene mammal fossils helped to locate the base of the Tertiary. These vertebrate fossil are normally not abundant in continental strata, thus in most areas they did not allow for a precise placement of the K-T interface.

Exacerbating the problem, the endemic nature of vertebrate faunas in the northern and southern parts of the Western Interior of North America made correlations of these fossils difficult. Plant fossils, being much more abundant in most continental strata, have proven to be a much more valuable biochronologic tool.

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