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The article examines the debate among scientists regarding how a nearly 1,200 year cold snap on Earth, called the Younger Dryas, began about 12,800 years ago. It covers the theory that a comet or its remnants hit or exploded over the Laurentide Ice Sheet despite the lack of a crater discovered to prove the hypothesis.

The article looks at research on the history of the solar system, focusing on the question of where the water on Earth originated. It explains why the scientific consensus has shifted from comets to asteroids hitting Earth as the source of its water, noting it initially formed as a rocky planet with no water. Topics include heavy water, or water containing deuterium, and the role of Jupiter and Saturn in causing the motion of asteroids and comets.

The article discusses the discovery of a meteorite crater near Hiawatha Glacier in Greenland, with a particular focus on implications for the Younger Dryas period. An overview of the Younger Dryas impact hypothesis, which maintains that the comet explosion was responsible for the cold temperatures during this period, is provided.

The article discusses a study by geochemist Morgan of Schaller of Rensselaer Polytechnic Institute on the relationship of impact debris and evidence of widespread wildfires around eastern North America to the start of the Paleocene-Eocene Thermal Maximum (PETM). It notes that large comet shattered the Earth 56 million years ago may have caused global warming and the rise of carbon dioxide levels. Micropaleontologist Megan Fung also proposes that charcoal was formed during the wildfires.

The article discusses a study by David Nesvorný and colleagues in the December 8, 2014 issue of the journal "Proceedings of the National Academy of Sciences" that suggests the energy produced by impacts of asteroids and comets could have produced RNA nucleobases necessary for life on Earth. The team zapped the nitrogen-containing compound formamide with a laser and found that the resulting radicals created 2,3-diaminomaleonitrile, which went on to form RNA nucleobases.

Information about a report presented by researchers at the American Chemical Society Fall 2009 Meeting in Washington, D. C., from August 16-20 is presented. According to a scientist at the U.S. National Aeronautics & Space Administration's (NASA) Goddard Space Flight Center, Jamie Elsila, samples of a building block of proteins which were found in the halo of an icy comet suggest that early life on Earth may have originated from space.

This article reports that evidence unearthed at more than two dozen sites across North America suggests that an extraterrestrial object exploded in Earth's atmosphere above Canada about 12,900 years ago, just as the climate was warming at the end of the last ice age. The explosion sparked immense wildfires, devastated North America's ecosystems and prehistoric cultures, and triggered a millennium-long cold spell, scientists say.

The article looks at a Web site that lets you evaluate how severe an astroid collision with the earth will be. You have just heard that an asteroid or a comet is about to wallop Earth and you might be in the vicinity. On the Web site, type in your distance from the predicted impact site, as well as the size and kind of projectile, and an easy-to-use program calculates the energy of the impact and the extent of the hole it will gouge. The program also estimates the size of the fireball to be created by the impactor, when the maximum amount of heat will be given off, the strength of the shock wave that will travel through the atmosphere, and where any kicked-up debris will land. To calculate the searing heat from the impact, the program relies on techniques from a 1977 government handbook on nuclear weapons. Developed by undergraduate Robert Marcus of the University of Arizona in Tucson, in collaboration with university astronomers H. Jay Melosh and Gareth Collins, the Internet site debuted on April 7, 2004.

Reports on research which indicates that an impact from space, possibly a comet or asteroid, caused the massive wave of extinctions on Earth 250 million years ago. Study of Japanese and Chinese rocks which date from end of Permian period; Discovery of molecules known as fullerenes or buckyballs in sediment from the period; Report by geochemist Luann Becker and colleagues at University of Washington in Seattle, in February 23, 2001 issue of journal 'Science'.

This article discusses research being done on the traces of asteroid or comet impact in Cuba. The asteroid or comet that purportedly snuffed out the last remaining dinosaurs some 65 million years ago may have slammed into the Earth just south of Cuba, according to speculations by Bruce F. Bohor of the U.S. Geological Survey in Denver, Colorado and Russell Seitz of Cambridge, Massachusetts. Since 1979, when researchers first raised the impact theory, a number of investigators have proposed locations in Iowa, the Indian Ocean and elsewhere as possible sites for the impact at the boundary between the Cretaceous and Tertiary (K/T) periods. Bohor and others have long proposed that the impact occurred in the vicinity of North America, because the largest pieces of shocked mineral grains--apparently from the impact--appear on that continent. The Caribbean attracted attention as a possible site in 1989 after Alan Hildebrand and William V. Boynton of the University of Arizona in Tucson discovered an unusually thick K/T sediment layer in Haiti containing pieces of glassy stone chips, often taken as evidence of an impact. This evidence led Hildebrand and Boynton to propose an impact off the coast of Colombia. After studying geologic reports written in the 1930s and 1940s, however, Bohor and Seitz speculate the extraterrestrial body hit south of western Cuba.

This article discusses the cause of the Earth's magnetic field reversal. A close examination of sediment cores from the deep sea is challenging the theory that comet or meteorite impacts have caused the Earth's magnetic field to reverse itself several times during geologic history. Scientists proposed this theory 20 years ago when they noted that a turnover in the geomagnetic field 730,000 years ago coincided in timing with an impact, marked in the geologic record by tiny, glassy grains called microtektites. Since then researchers have found two other close timings between impacts and reversals 15 million years ago and 900,000 years ago, seemingly bolstering the original theory. But a study of the event 900,000 years ago suggests the impact followed the reversal and could not have caused it. The researchers studied a layer of microtektites buried in sediments near the Ivory Coast. They discovered the microtektite layer above the sediment layer that recorded the reversal and estimated the impact occurred 30,000 years after the beginning of the reversal. Dennis V. Kent of the Lamont-Doherty Geological Observatory concedes that a reversal 730,000 years ago did directly follow an impact, but he notes neither the K-T impact 65 million years ago nor one 15 million years ago are clearly linked to a reversal.

Reports criticism of the theory that the Earth is bombarded by house-sized snowballs each day. Theory of Louis A. Frank, University of Iowa, Iowa City; Criticisms published in the December 15, 1997 edition of `Geophysical Research Letters'; Role of camera images from the Dynamics Explorer 1 satellite; Sources of criticism; Frank's response.

Reports on research investigating evidence that a comet or other giant body slammed into South Africa at the close of the Jurassic period. The crash as a possible explanation for a surge in extinctions among reptiles and marine life around the same time; The publication of the research by Christian Koeberl and colleagues in the August 1997 `Geology.'

Focuses on a study of a 16-inch core of mud from the ocean floor east of Jacksonville, Florida which provides clues of how life on Earth suffered after a comet or meteor slammed into the planet about 65 million years ago. How this enters the debate about the mass extinction at the end of the Cretaceous period; The announcement of findings in 1997 by Robert W. Corell and Richard D. Norris.

Reports on speculations regarding a fireball that struck the ground on June 30, 1908 in the remote Tunguska River valley of Siberia. Collision of a comet with the earth; Presence of abnormal amounts of radiocarbon in tree-rings that grew in 1909.