What is a meteor?
A meteor (“shooting star”) is the passage of a space debris (small asteroid piece – rock or metal; or comet piece) into the Earth’s atmosphere. They are heated by high speed friction with air particles in the upper atmosphere, and shed glowing material in its wake, sufficient to create a visible streak of light. They typically occur at altitudes from 76 to 100 km (47 to 62 mi). The root word meteor comes from the Greek meteōros, meaning “high in the air”.
Millions of tiny meteors occur in the Earth’s atmosphere daily. Most are about the size of a grain of sand. Meteors may occur in showers, which arise when the Earth passes through a stream of debris left by a comet. They may occur as “random” or “sporadic” meteors, not associated with a specific stream of space debris. Some meteors have been tracked with enough detail, so we know the asteroid that they likely came from.
The atmospheric velocities of meteors result from the movement of Earth around the Sun at about 30 km/s (18 miles/second), the orbital speeds of meteoroids, and the gravity well of Earth.
They become visible between about 75 to 120 km (47 to 75 mi) above the Earth. They usually disintegrate at altitudes of 50 to 95 km (31 to 59 mi).
Meteor impacts on Earth
Meteor impacts on Earth
Impact Craters North America: See the Chesapeake Bay impact crater
Click-and-zoom to see craters worldwide
The Smoking Gun: Chicxulub crater and the dinaosaurs
Chicxulub Crater, Mexico, and the Cretaceous – Tertiary boundary
Two Tunguskas in South America in the 1930s
‘There is evidence that there were two massive bolide explosions which occurred over South America in the 1930’s. One seems to have occurred over Amazonia, near the Brazil-Peru border, on August 13, 1930, whilst the other was over British Guyana on December 11, 1935. It is noted that these dates coincide with the peaks of the Perseids and the Geminids, although any association with those meteor showers is very tentative. The identification of such events is significant in particular in that they point to the need for re-assessment of the frequency of Tunguska-type atmospheric detonations.”
1954, Melrose, Massachusetts
Was a 1954 explosion over Melrose caused by jets? Or a tiny meteor?
By Carolyn Y. Johnson, Boston Globe, 02.20.13
Meteor air burst in Russia, 2013
Did Dinosaur-killing Asteroid Trigger Largest Lava Flows on Earth?
May 1, 2015, Released by University of California – Berkeley
The asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe that may have contributed to the devastation, according to a team of University of California, Berkeley, geophysicists.
Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India known as the Deccan Traps, explaining the “uncomfortably close” coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.
“If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule,” said team leader Mark Richards, UC Berkeley professor of earth and planetary science. “It’s not a very credible coincidence.”
Richards and his colleagues marshal evidence for their theory that the impact reignited the Deccan flood lavas in a paper to be published in The Geological Society of America Bulletin, available online today (April 30) in advance of publication.
While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after re-ignition, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it’s still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs, Richards said.
“This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn’t yet take us closer to understanding what actually killed the dinosaurs and the ‘forams,'” he said, referring to tiny sea creatures called foraminifera, many of which disappeared from the fossil record virtually overnight at the boundary between the Cretaceous and Tertiary periods, called the KT boundary. The disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.
He stresses that his proposal differs from an earlier hypothesis that the energy of the impact was focused around Earth to a spot directly opposite, or antipodal, to the impact, triggering the eruption of the Deccan Traps. The “antipodal focusing” theory died when the impact crater, called Chicxulub, was found off the Yucatán coast of Mexico, which is about 5,000 kilometers from the antipode of the Deccan traps….