When was kt extinction

If indeed the spike was formed by a large impact, what other evidence should we hope to find in the rock record? Well-known meteorite impact structures often have fragments of shocked quartz and spherules tiny glass spheres associated with them Figure The glass is formed as the target rock is melted in the impact, blasted into the air as a spray of droplets, and almost immediately frozen. Over geological time, the glass spherules may decay to clay.

Shocked quartz is formed when quartz crystals undergo a sudden pulse of great pressure. If they are not heated enough to melt, they may carry peculiar and unmistakable microstructures Figure It is only a few millimeters thick, but in total it contains more than a cubic kilometer of shocked quartz in North America alone. The zone of shocked quartz extends west onto the Pacific Ocean floor, but shocked quartz is rare in K-T boundary rocks elsewhere: some very tiny fragments occur in European sites.

All this evidence implies that the K-T impact occurred on or near North America, with the iridium coming from the vaporized asteroid and the shocked quartz coming from the continental rocks it hit. The K-T impact crater has now been found. The structure is about km across, one of the largest impact structures so far identified with confidence on Earth.

A borehole drilled into the Chicxulub structure hit meters more than feet of igneous rock with a strange chemistry. That chemistry could have been generated by melting together a mixture of the sedimentary rocks in the region.

The igneous rock under Chicxulub contains high levels of iridium, and its age is 65 Ma, exactly coinciding with the K-T boundary. On top of the igneous rock lies a mass of broken rock, probably the largest surviving debris particles that fell back on to the crater without melting, and on top of that are normal sediments that formed slowly to fill the crater in the shallow tropical seas that covered the impact area.

Well-known impact craters often have tektites associated with them as well as shocked quartz and tiny glass spherules. Tektites are larger glass beads with unusual shapes and surface textures.

They are formed when rocks are instantaneously melted and splashed out of impact sites in the form of big gobbets of molten glass, then cooled while spinning through the air. Haiti was about km from Chicxulub at the end of the Cretaceous Figure At Beloc and other localities in Haiti, the K-T boundary is marked by a normal but thick 30 cm clay boundary layer that consists mainly of glass spherules Figure The clay is overlain by a layer of turbidite, submarine landslide material that contains large rock fragments.

Some of the fragments look like shattered ocean crust, but there are also spherical pieces of yellow and black glass up to 8 mm across that are unmistakably tektites. The black tektites formed from continental volcanic rocks and the yellow ones from evaporite sediments with a high content of sulfate and carbonate. Above the turbidite comes a thin red clay layer only about mm thick that contains iridium and shocked quartz.

One can explain much of this evidence as follows: an asteroid struck at Chicxulub, hitting a pile of thick sediments in a shallow sea. The impact melted much of the local crust and blasted molten material outward from as deep as 14 km under the surface. Small spherules of molten glass were blasted into the air at a shallow angle, and fell out over a giant area that extended northeast as far as Haiti, several hundred kilometers away, and to the northwest as far as Colorado.

Next followed the finer material that had been blasted higher into the atmosphere or out into space and fell more slowly on top of the coarser fragments.

This accounts in particular for the tremendous damage to the North American continent, and the skewed distribution of shocked quartz far out into the Pacific. Other sites in the western Caribbean suggest that normally quiet, deep-water sediments were drastically disturbed right at the end of the Cretaceous, and the disturbed sediments have the iridium-bearing layer right on top of them.

At many sites from northern Mexico and Texas, and at two sites drilled on the floor of the Gulf of Mexico, there are signs of a great disturbance in the ocean at the K-T boundary. In some places, the disturbed seafloor sediments contain fossils of fresh leaves and wood from land plants, along with tektites dated at 65 Ma Figure Around the Caribbean and at sites up the Eastern Atlantic coast of the United States, existing Cretaceous sediments were torn up and settled out again in a messy pile that also contains glass spherules of different chemistries, shocked quartz fragments, and an iridium spike.

All this implies that a great tsunami or tidal wave affected the ocean margin of the time, washing fresh land plants well out to sea and tearing up seafloor sediments that had lain undisturbed for millions of years. The resulting bizarre mixture of rocks has been called "the Cretaceous-Tertiary cocktail.

This first hot fireball blew vaporized and molten debris including glass spherules and iridium high above the atmosphere to be deposited last and globally as it slowly drifted downward. The larger fragments, solid and molten, were blasted outward at lower angles, but not very far, and were deposited first and locally about 15 minutes travel time to Colorado!

At the same time, smaller fragments, including shocked quartz, were blown upward between the hot fireball and the larger fragments, and were deposited second and regionally about 30 minutes to reach Colorado. The impact energy, for comparison with hydrogen bomb blasts, was around million megatons. A Giant Volcanic Eruption? Exactly at the K-T boundary, a new plume Chapter 6 was burning its way through the crust close to the plate boundary between India and Africa.

Enormous quantities of basalt flooded out over what is now the Deccan Plateau of western India to form huge lava beds called the Deccan Traps.

A huge extension of that lava flow on the other side of the plate boundary now lies underwater in the Indian Ocean Figures The Deccan Traps cover , km2 now about , square miles , but they may have covered four times as much before erosion removed them from some areas.

They have a surviving volume of 1 million km 3 , cubic miles and are over 2 km thick in places. The entire volcanic volume that erupted, including the underwater lavas, was much larger than this Figure Furthermore, the Deccan eruptions began suddenly just before the K-T boundary.

The rate of eruption was at least 30 times the rate of Hawaiian eruptions today, even assuming it was continuous over as much as a million years; if the eruption was shorter or spasmodic, eruption rates would have been much higher. The Deccan Traps probably erupted as lava flows and fountains like those of Kilauea, rather than in giant explosive eruptions like that of Krakatau.

But estimates of the fire fountains generated by eruptions on the scale of the Deccan Traps suggest that aerosols and ash would easily have been carried into the stratosphere. Thus there is strong evidence for short-lived but gigantic volcanic eruptions at the K-T boundary. Some people have tried to explain all the features of the K-T boundary rocks as the result of these eruptions. Yet some species of cold-blooded animals, such as crocodiles, did manage to survive. Also, climate change would have taken tens of thousands of years, giving the dinosaurs sufficient time to adapt.

In , Russian astronomer Joseph Shklovsky became the first scientist to consider the extinction was due to a single catastrophic event when he theorized that a supernova the explosion of a dying star showered the earth in radiation that could have killed the dinosaurs. Once again, the problem with the theory was explaining why dinosaurs died out and other species did not.

Also, scientists said that such an event would have left evidence on the surface of the earth—trace amounts of radiation dating back to the Cretaceous Period. None was found. Enter Luis Alvarez, a Nobel Prize-winning physicist, inventor and pioneer in the field of radiation and nuclear research. He and his son, noted geologist Walter Alvarez, were conducting research in Italy when they discovered a centimeter-thick layer of iridium-enriched clay at the K-T boundary.

Iridium is rare on earth, but more common in space. The Alvarezes published their findings in , postulating that the thin layer of iridium was deposited following the impact of a large meteor, comet or asteroid with the earth. At the time, the Alvarez theory was so far removed from prevailing hypotheses that it was ridiculed. Slowly, though, other scientists began finding iridium evidence at various places around the globe that corroborated the Alvarez theory.

There was, however, no smoking gun in the form of an impact site. The Chicxulub Crater, as it was dubbed, was named for a nearby village. Scientists believe the bolide that formed it was roughly 6 miles in diameter, struck the earth at 40, miles per hour and released 2 million times more energy than the most powerful nuclear bomb ever detonated. Miles-high tsunamis would have washed over the continents, drowning many forms of life.

Shock waves would have triggered earthquakes and volcanic eruptions. The resulting darkness could have lasted for months, possibly years. Many dinosaurs would have died within weeks. The carnivores who feasted on the herbivores would have died a month or two later.

Overall, the loss of biodiversity would have been tremendous. Only small scavenging mammals that could burrow into the ground and eat whatever remained would have survived. The iridium layer plus the Chicxulub Crater were evidence enough to convince many scientists that the bolide impact theory was credible. It explained much of what previous theories could not.

Paleontology remains a competitive discipline even though its central mystery appears to have been solved. Agreement over dinosaur extinction is far from unanimous, and fossils continue to be found that add to the body of knowledge about how the dinosaurs lived and died.

Only recently have birds been identified as descendants of the dinosaurs, and theories regarding dinosaur intelligence and behavior continue to change. The climate change theory still holds sway over some scientists, who refute that the Chicxulub impact was the sole cause of the extinction.

Evidence from the million-year-old lava flows in India hint that a giant, gaseous volcanic plume might have initiated global climate change that threatened the dinosaurs. But if you see something that doesn't look right, click here to contact us! Subscribe for fascinating stories connecting the past to the present. The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period of the Mesozoic Era, some million years ago.

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