![]() ![]() From studies of orbit statistics, it is estimated that asteroids of 10 km size can hit the earth roughly every 100 My or so - which fits with the idea that we actually did get hit 65 My ago by an object this size. Astronomers have charted numerous asteroids that cross Earth's orbit.It is revealed by mapping the strength of the gravity field over that area, and by drilling it has been dated to 65 My old. It is no longer visible on the surface of the Earth, but is buried under sediments. After a decade of searching, scientists in 1990 identified the crater associated with this material.The same soil layer, especially around the Gulf of Mexico, contains massive deposits of tumbled boulders, as would be generated in a large tsunami, or "tidal wave." The geographic distribution of tsunami deposits suggest the impact was in the Caribbean area.This suggests that massive fires were touched off at the time of impact. The same soil layer contains enough soot to correspond to burnding down all of the forests of the world.(The deformation is a microscopic structure called "twinning," in the crystals). The same soil layer contains grains of quartz that were deformed by high shock pressures, as would occur in a giant explosion.The iridium excess in the 65 My-old soil layer has been confirmed at many points around the world.There are now many lines of evidence to prove that a relatively large impact happened 65 My ago. However, compelling evidence has accumulated to support the theory. Therefore, the Alvarez team theorized that an asteroid had hit Earth at this time, and that the debris ejected from the explosion were spread in the soil layer.įor about ten years, this theory was extremely controversial. Meteorites are believed to be fragments of asteroids. In the soil layer that separates the Mesozoic Era from the Cenozoic Era, dating 65 My ago, they found an excess of the element iridium, which is common in meteorites. In the late 1970s, a team of geochemists headed by Luis Alvarez and his son Walter Alvarez, both with connections to the University of California at Berkeley, was studying chemical changes in soil layers corresponding to breaks in the fossil record. Prior to the 1980s, the causes of the breaks were unknown. For example, the Paleozoic era gave way to the Mesozoic era of middle life forms, which in turn gave way to the present Cenozoic era of recent life. Indeed, these breaks were the basis for dividing geologic time into different eras with different names. Mammals were not common until after 65 My ago, and humanlike creatures appeared only in the last 4 My.Įver since the fossil sequence began being mapped around 1800, geologists noticed that striking "breaks" occurred in the sequence, when one group of fossilized species gave way to other groups during short intervals. Fish fossils appear in strata after about 500-600 My ago dinosaurs and giant reptiles were on the land by 200 My ago. For example, 1000 million years (abbreviate My) ago, the oceans held only simple organisms like algae, while the land was relatively lifeless. Gaps in the Fossil Recordįossils found in soil layers of different ages show a record of slow, gradual changes in species, with simple organisms gradually being replaced by more complex organisms, apparently by evolutionary processes driven by natural selection. Most, but not all are smaller than the one that hit us 65 million years ago. Some of these could potentially hit Earth in the future. Many asteroids of this type are now known their orbits pass through the inner solar system and cross Earth's orbit. Debris from the explosion was thrown into the atmosphere, severely altering the climate, and leading to the extinction of roughly 3/4 of species that existed at that time, including the dinosaurs. ![]() ![]() This impact made a huge explosion and a crater about 180 km (roughly 110 miles) across. BermanĪccording to abundant geological evidence, an asteroid roughly 10 km (6 miles) across hit Earth about 65 million years ago. ![]()
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