March 9, 2016

Next month, in April, a deep-ocean drilling project will begin off the Yucatán coast in the Gulf of Mexico. Most such oceanic drill projects are concerned with oil exploration. This isn’t your usual drill team, however. The drillers in this case come from the International Ocean Discovery Program, the National University of Mexico, and the University of Texas. And they will be drilling into Chicxulub Crater, an impact crater formed by a giant asteroid that helped kill the dinosaurs some 65 million years ago. They won’t be looking for oil; they’ll be looking for answers.

The Chicxulub Crater along the northern coast of Mexico’s Yucatán Peninsula formed when an asteroid hit the earth about 65 million years ago. Debris from the impact may have led to the extinction of the dinosaurs.
Credit: WORLD BOOK map

At the end of the Cretaceous Period, dinosaurs were the dominant land animals on the planet. Other reptiles filled the seas, and birds—descendants of dinosaurs—roamed the skies. Mammals existed, but they were far smaller and less common than today. Then, an asteroid at least 6 miles (10 kilometers) wide slammed into the Yucatán Peninsula, in present-day Mexico. The impact threw up large amounts of gas and dust into the atmosphere. This material would have blotted out the sun for many years. Plants that use sunlight to make their food would have died out, followed by the animals that ate them. With no more prey animals, large carnivores starved as well.

When the dust settled, about half of all species on Earth had gone extinct. All the dinosaurs—except birds—were dead. Only a few kinds of other reptiles survived. Mammals survived too and over time evolved to become the dominant large-bodied animals on land and in the sea.

The Yucatán asteroid formed a large impact crater, which is now partly on the peninsula and partly in the Gulf of Mexico. Tens of millions of years of plate tectonics and erosion have taken their toll on the crater, and it is barely visible in satellite images today. But the mark that it left in the rocks should still be clear.

The team plans to use a drilling ship to sample rock deep beneath the ocean floor. In drilling into the crater, scientists hope the presence (or lack) of microfossils (tiny preserved remains of ancient organisms) will teach them more about the nature of the asteroid impact and how quickly life returned to the area afterwards.

The drilling evidence may also better explain how responsible the impact was for the mass extinction at the end of the Cretaceous Period. Most scientists agree that the asteroid did most of the damage, but others argue that other causes, such as massive volcanic activity in present-day India, were more to blame. Such extinction hypotheses are not mutually exclusive, however: it may have taken more than one disaster to knock out the dinosaurs. In fact, they may even be linked. Recent studies have suggested that the Yucatán impact caused the spike in volcanism on the other side of the globe in India. Whatever the case, the drilling team will help get to the bottom of this and other stories, as well as to the bottom of the impact crater itself!

April 1, 2014

A single-celled organism that was a glutton for nickel may have played a key role in the most devastating mass extinction in Earth’s history. The Permian Extinction took place some 252 million years ago. It is informally known as “The Great Dying” because at least 90 percent of all living species on Earth perished over the short (geologically speaking) period of about 60,000 years. Even insects, which largely escaped other mass extinctions, were hit hard. Scientific theories for the die-off have included global warming, global cooling, meteorite impacts, disease, blasts of radioactive cosmic rays from space, and–the favorite–massive volcanic eruptions. Volcanoes have come under suspicion because of the Siberian Traps, about 480,000 cubic miles (2 million cubic kilometers) of preserved flood basalts (layers of volcanic rock) dating from the end of the Permian Period in western Siberia. In the longest-known continuous volcanic eruption in Earth’s history, Siberian volcanoes spewed out enough lava to cover Earth to a depth of 10 feet (3 meters).

Now a team of researchers headed by Daniel Rothman of the Massachusetts Institute of Technology is arguing that the volcanoes were only “accessories to the crime.” The main cuplrit, they contend, was a group of microbes called Methanosarcina. These methane-producing microbes are archaea, organisms that make up one of three basic divisions of life. According to the researchers, Methanosarcina grew explosively in the oceans, releasing massive amounts of methane. Methane is an even more potent greenhouse gas than carbon dioxide (CO2). In fact, molecule for molecule, methane traps about 25 times as much atmospheric heat as does CO2. The methane from the microbes dramatically changed the chemistry of the atmosphere and the oceans, making Earth’s climate toxic to nearly all species.

Mount Etna is an active volcano on the island of Sicily. Major eruptions of the volcano spew molten lava and endanger nearby villages. The eruption shown here began on July 18, 2001. AP/Wide World

Rothman and his team presented three lines of evidence to support their theory. First, they pointed to a huge increase in CO2 levels in the oceans at the end of the Permian Period. As ocean waters absorbed the CO2, they would have become increasingly acidic. Devastating losses in marine organisms, particularly those with shells, would have resulted. Second, the researchers determined that about 251 million years ago, Methanosarcina picked up a gene from another microbe that enabled it to rapidly convert carbon into methane. Even with practically unlimited amounts of carbon at their disposal, the microbes would still have needed an esssential nutrient–nickel–to support their new lifestyle. According to the scientists, that’s where the Siberian volcanoes came in. Lava from the volcanoes produced the world’s largest nickel deposits. The nickel somehow reached the oceans, causing a feeding frenzy among the microbes. That explosion in atmospheric methane essentially suffocated most of the life on Earth.

After the Permian extinction, life took at least 5 million years to recover–that is, to evolve a wide variety of species. In the oceans, complex mollusks, crustaceans, and fish, which could swim easily from place to place, become more widespread and common. On land, surving plants and animals evolved into a variety of forms, including coniferous trees and insect-eating mammals. The extinctions of Permian animals also paved the way for the dinosaurs.

Additional World Book articles:

• Methane: Another Greenhouse Troublemaker (a Special Report)
• The Biggest Eruptions on Earth (a Special Report)
• The Ocean’s Changing Chemistry: Tipping the Balance? (a Special Report)

Jan. 27, 2012

An asteroid–a 36-foot (11-meter) space rock named 2012 BX3–hurtled past Earth today, coming as close as 37,280 miles (60,000 kilometers). “It’s one of the closest approaches recorded,” noted Gareth Williams, associate director of the Minor Planet Center at Cambridge, Massachusetts. “It makes it in to the top 20 closest approaches, but it’s sufficiently far away . . . that there’s absolutely no chance of it hitting us.” Scientists believe that asteroids are chunks of material left over from the formation of the solar system. The gravitational pull of the planet Jupiter probably prevented these pieces from coming together to form a full-sized planet. Some asteroids may represent the nuclei (cores) of comets that are no longer active.

The asteroid Ida and its tiny moon Dactyl appear in a photograph taken by the U.S. spacecraft Galileo. Dactyl may be a piece of Ida that broke away during a collision with another asteroid. NASA/JPL/Galileo Project

The atmosphere protects Earth from most asteroid strikes. Air friction causes an asteroid smaller than about 160 feet (50 meters) in diameter to disintegrate before it can reach the surface and cause damage. Larger asteroids can impact the environment of the entire globe. The impact of an asteroid with a diameter of around 0.6 mile (1 kilometer) would kick large amounts of dust into the atmosphere. The dust would block sunlight, which would cool the air for many months. One such strike occurred 65 million years ago on Mexico’s Yucatan Peninsula. Many scientists think environmental damage caused by the collision led to a mass extinction. The extinction eliminated huge numbers of species, including the dinosaurs.

Additional World Book articles:

• Dawn
• Eros
• Vesta
• When Worlds and Comets Collide (a special report)
• What Has Caused Mass Extinctions (a special report)