Impact on EARTH Magazine

Impact signature in rock produced by lightning strikes

Thu, 14 Dec 2017 15:47:34 -0500

A new study suggests that lighting strikes can create shock features on rocks that were previously thought to form only as a result of meteorite impacts. Credit: public domain.

When a meteorite smashes into Earth’s rocky surface, the immense temperatures and pressures created can melt rock into glass and leave signatures of the impact behind. Impacts produce tell-tale planar features in quartz grains called shock lamellae — picture a scrambled television signal, with repeating horizontal lines chopping and distorting the image into layers — that scientists have thought were produced only by meteorites.

Minerals deformed by meteorites reveal age of impact

Tue, 19 Sep 2017 11:30:41 -0400

The Willamette Meteorite on display at the American Museum of Natural History in New York City. Credit: Dante Alighieri, CC BY-SA 3.0.

Researchers have discovered a new way to determine when a meteorite hit Earth, a technique that could not only help scientists date ancient meteorite strikes but also determine when planetary crusts first formed.

Platinum may point to impact theory for Younger Dryas

Fri, 16 Jun 2017 14:52:51 -0400

Archaeologists found an abundance of platinum — an element that can be associated with cosmic objects like asteroids or comets — at 11 Clovis excavation sites across the United States. Credit: K. Cantner, AGI.

Some large meteorite strikes leave obvious craters on Earth’s surface, while others that hit water or ice or explode in the air may only leave subtle markers in the soil, such as exotic minerals or elevated levels of rare elements like platinum or iridium. In a new study, researchers report spikes of platinum in sediments at archaeological sites across North America, offering new evidence, they suggest, of a major meteorite strike about 12,800 years ago, just before the onset of a global cold period known as the Younger Dryas. The lack of a telltale crater dating to this time, however, has left scientists debating for years whether an impact actually occurred and what, if any, role it had in setting off the cold snap and affecting some of Earth’s human and animal populations.

Mystery impact may have kicked off dramatic warming event

Wed, 25 Jan 2017 13:55:37 -0500

Glassy spherules, found in 56-million-year-old clay layers along the New Jersey coast and near Bermuda, offer evidence of an impact that hit Earth at about the time of a rapid global warming event. Credit: Schaller et al., Science, October 2016.

About 56 million years ago, the planet warmed rapidly in a mysterious event known as the Paleocene-Eocene Thermal Maximum (PETM). Researchers recently discovered evidence in the rock record from around the same time that points to an extraterrestrial impactor striking Earth, but whether the two events are related is yet to be determined.

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

Thu, 31 Dec 2015 11:02:00 -0500

The mountains of basalt that remain hint at the scale of volcanism that heaped massive amounts of lava onto the Indian subcontinent around the time of the Cretaceous-Paleogene transition. Credit: Blair Schoene.

The Deccan Traps sprawl over more than half a million square kilometers of India. Credit: K. Cantner, AGI.

Few episodes in geologic history are as widely recognized as the Cretaceous-Paleogene, or K-Pg, boundary 66 million years ago. Utter “K-Pg,” “K-T” (for Cretaceous-Tertiary, as it’s still commonly known) or “end-Cretaceous” to any geoscientist and you’re virtually assured of a knowing glance as he or she recalls at least the textbook basics of a large bolide impact and mass extinction that finished off the dinosaurs and gave rise to the Age of Mammals. 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.

Meteorites might have created Earth's earliest continents

Wed, 23 Dec 2015 13:33:13 -0500

Earth and Venus were probably far more tectonically similar billions of years ago, when massive impacting meteorites could have triggered the creation of early continental crust, according to a new study. Credit: V.L. Hansen, Lithosphere, 2015.

Massive meteorite impacts on Earth are destructive events, gouging enormous craters in the crust and raining debris over the planet’s surface. But such huge impacts may have also created some of its earliest continental kernels, called cratons, during Archean times.

Geologic Column: The 'impact factor' of potholes

Tue, 22 Sep 2015 10:11:43 -0400

A pothole and "ejecta" debris near the author's house in Silver Spring, Md. Credit: Edward R. Landa.

Last winter was truly severe in the northeastern U.S. Snowfall records were blown away in cities like Boston, which finally saw its last snow pile melt away in mid-July. Even though last season’s snow is gone, residents spent months dealing with the recovery — especially in the form of fixing roads left with gaping roadway potholes. Hard-hit Massachusetts established a “Winter Recovery Assistance Program,” providing $30 million to help cities and towns fill potholes. But until they were filled, in Massachusetts and elsewhere, drivers had to endure seemingly endless bone-jarring shocks as their car tires dropped into the enormous and abundant potholes. Bumpily driving along one day last spring left me pondering potholes — from a geologic perspective.

Ancient asteroids boiled Earth's oceans

Mon, 21 Sep 2015 11:28:06 -0400

Donald Lowe and Gary Byerly examine Archean rocks that preserve evidence of impacts in South Africa. Credit: Donald Lowe.

The asteroid that wiped out the remaining dinosaurs — save for the avian variety — 66 million years ago was roughly 10 kilometers wide. Long before that, however, early Earth was bombarded by many larger impactors, which pulverized Earth’s surface time and again. Now, a new study published in Geology suggests that two asteroids, dating to Archean times and estimated to be 50 to 100 kilometers in diameter, released enough energy to boil the oceans and reduce sea level by as much as 100 meters or more.

Benchmarks: July 22,1960: Mineral discovery ends Meteor Crater debate

Mon, 08 Jun 2015 11:03:24 -0400

Meteor Crater near Flagstaff, Ariz. Credit: NASA Earth Observatory.

In 1923, Daniel Moreau Barringer stood on the edge of a vast bowl-shaped depression in the Arizona desert, watching a drill rig bore into the floor of the crater. Barringer had spent more than two decades exploring the massive hole, which lies on the Colorado Plateau 65 kilometers east of Flagstaff, Ariz. And although he had sunk dozens of drill holes, collected scores of samples, and carefully mapped the piles of talus that draped its concave walls, Barringer still hadn’t found what he was looking for, and he was getting nervous.

Giant bolide hit South Africa 2.5 billion years ago

Thu, 14 May 2015 12:05:43 -0400

Tiny spherules, like those seen in this rock found in Western Australia, form when vaporized rock from a meteorite impact condenses into small, round particles. Credit: Oberlin College photo/Bruce M. Simonson.

Some of the oldest scraps of continental crust on Earth cling to the southern tip of Africa and the western edge of Australia. In both places, geologists have found rock layers rich in tiny particles called spherules. Scientists think spherules form when meteorites strike the planet, vaporizing surface rocks that then condense into small droplets, blanketing the surrounding landscape. Now, research published in Geology confirms the extraterrestrial origin of a 2.5-billion-year-old layer of spherules in South Africa, which scientists say was produced by a bolide at least as large as the one that doomed the dinosaurs.

Mineral in Chelyabinsk meteorite reveals past collision

Tue, 04 Nov 2014 10:55:28 -0500

This fragment of the Chelyabinsk meteorite was retrieved from Lake Chebarkul in Russia. Credit: ©Shutterstock.com/Migel.

A new analysis of fragments of the Chelyabinsk meteorite — which burst over Chelyabinsk, Russia, in February 2013 — reveals that its parent asteroid collided with another asteroid nearly 300 million years before it struck Earth.

Africa's impact is one that even the dinosaurs would have seen coming

Tue, 12 Aug 2014 18:37:46 -0400

An artist's rendering of an asteroid impacting Earth. Credit: NASA/Don Davis.

The crater left by the infamous Chicxulub asteroid responsible for finishing off the dinosaurs about 65 million years ago, was more than 19 kilometers deep and 177 kilometers in diameter. Those dimensions correspond to a huge energy release estimated at 100 teratons of TNT, but that’s puny compared to an impact that struck South Africa’s Barberton Greenstone Belt about 3.26 billion years ago. Now, researchers have estimated just how big that massive asteroid was and the catastrophic effect it might have had on Earth and its budding plate tectonic system.

Acid oceans followed Chicxulub impact

Fri, 08 Aug 2014 10:36:16 -0400

The proposed mechanism by which the oceans could have been acidified within days after the Chicxulub impact 65.5 million years ago. Credit: Kathleen Cantner, AGI.

Within days after the massive Chicxulub impact that ended the Cretaceous Period 65.5 million years ago, a deluge of acid rain may have turned Earth’s ocean surfaces into suddenly inhospitable homes for a multitude of microorganisms, ultimately pushing them to extinction, according to a new study.

Ancient seawater found in Chesapeake Bay impact crater

Fri, 18 Jul 2014 17:38:17 -0400

When the bolide struck in the Late Eocene, it shattered the bedrock, truncated aquifers and left a crater roughly twice the size of Rhode Island and nearly as deep as the Grand Canyon. The resulting structural low is likely responsible for the formation of the Chesapeake Bay.

Lessons from the Russian meteor burst

Mon, 12 May 2014 14:53:24 -0400

A 3-D simulation of the Chelyabinsk airburst. Credit: Andrea Carvey, Mark Boslough & Brad Carvey

At about 9:20 a.m. on Feb. 15, 2013, many of those cameras recorded the explosion of a large meteor 23 kilometers above the city. As was widely reported at the time, the air blast shattered windows, and meteorite fragments rained down in and around Chelyabinsk, causing damage to some 7,000 buildings and sending about 1,600 people to hospitals. Although no one was killed, it marks “the first ever asteroid impact disaster in human history,” according to Clark R. Chapman of the Southwest Research Institute (SwRI) Planetary Science Directorate in Boulder, Colo., who presented research on the event at the annual meeting of the American Geophysical Union (AGU) in San, Francisco, Calif., last December.

Iowa impact crater confirmed

Thu, 13 Jun 2013 12:21:53 -0400

An airborne geophysical survey has confirmed the discovery of an impact crater under the town of Decorah in northeastern Iowa. Adam Kiel, U.S. Geological Survey

An airborne geophysical survey mapping mineral resources in the Midwest has confirmed that a 470-million-year-old impact crater nearly five times the size of Barringer (Meteor) Crater in Arizona lies buried several hundred meters beneath the town of Decorah, Iowa.

Do impacts trigger extinctions? Impact theory still controversial

Thu, 05 Jan 2012 06:41:58 -0500

AGI

The revolution started with a bang in 1980. For some, this revolution became a religion, even an orthodoxy. The true believers became proselytes and began to see signs supporting their viewpoint everywhere. But each time the proselytes claimed to have found yet another example in support of their “religion,” naysayers and doubters emerged. Two sides formed, each loudly castigating and questioning their opponents.

Giant dunes, not mega-tsunami deposits?

Thu, 05 Jan 2012 06:41:58 -0500

Some models suggest the chevrons' orientations (black arrows) don't match the direction of arriving tsunami waves (white arrows). Robert Weiss

Tsunamis generated by asteroid impacts may have left white, sandy "chevron" deposits in Madagascar. Robert Weiss

About four years ago, a group of scientists proposed that a series of giant, wedge-shaped sandy deposits found along the shores of southern Madagascar might be evidence of a giant tsunami — a “mega-tsunami” — generated by an asteroid that may have blasted into the Indian Ocean sometime in the last 10,000 years. Furthermore, the scientists said, such impacts and the resulting tsunamis may have occurred fairly frequently during this period. To search for evidence of these impacts, the researchers formed the Holocene Impact Working Group. By 2006, with the help of Google Earth, they found dozens more of the wedge-shaped deposits, called chevrons, scattered across the planet, including in Africa, Australia and the United States.

Santa Fe impact crater discovery: A series of fortunate events

Thu, 05 Jan 2012 06:41:58 -0500

Tim McElvain stands with the Santa Fe impact structure shatter cones along Highway 475. Annika Wallendahl

Along the Chamisa Trail, a popular hiking destination about a 15-minute drive northeast of Santa Fe, Tim McElvain found the first Santa Fe shatter cones in 2003. Annika Wallendahl

One of the definitive shatter cones revealed by a rockslide on Highway 475. Annika Wallendahl

Tim McElvain spent countless hours over close to a decade poring over the evidence of the Santa Fe impact. Annika Wallendahl

In the ancient pink and orange hills of the Sangre de Cristo Mountains, Thornton “Tim” McElvain, a retired petroleum geologist, leads me over a concrete highway barrier to a towering granite road cut. McElvain steps onto a rock pile and points to a meter-long block of granite, the freshest offering to fall from the rock face. One side of the block tapers roughly to the shape of a cone, with grooves coming together to form a point.

Travels in Geology: Chesapeake Bay, from impact craters to executive orders

Thu, 05 Jan 2012 06:41:58 -0500

NASA's Landsat satellite mosaic of the Chesapeake Bay. NASA

Sharps Island lighthouse, in Chesapeake Bay, is partially submerged. Skip Willits

Scenic and fragile, tidal wetlands are a crucial part of the Chesapeake Bay ecology. Copyright January 2006 Jennifer Schmidt.

The lower part of the Chesapeake Bay offers more than crab cakes and boating. Today, the bay is central to one of country’s largest environmental campaigns. But an excursion around the Virginian coasts provides an amazing peek into the mid-Atlantic region’s rich geological, environmental and cultural history, spanning impact events, glaciation, early colonial settlements and modern struggles with pollution and rising sea level.