Still defenseless Earth remains vulnerable to the Big One
By Jay Brodell
At any moment a large rock can plummet from space and wipe out all or part of civilization. That realization should put into perspective all other day-to-day concerns.
A quick look at the airless moon’s surface shows the battering celestial objects take. On Earth natural geological processes cover up impact craters from meteors, asteroids and comets.
Scientists in many countries are keeping track of the nearby rocks. The effort to provide some kind of protection against doomsday still is in infancy.
Time was when scientists speculated that a damaging meteor impact would take place every couple of hundred thousand years. Now research shows that the probability is much more frequent. There are at least three instances in modern times when meteors changed the course of civilization. The most recent may have been just 500 years ago when twin space rocks struck just off the coast of Australia in the Gulf of Carpentaria. A student team at Cardiff University studied tree rings there to show that something around 535 A.D. shocked the world into a mini ice age. Researchers at the University of Wollongong in Australia supported this view and speculated that a meteor broke apart into two one-kilometer chunks before slamming into the ocean.
The world’s oceans hide many meteor craters. Scientists track them by the remains of tsunamis that throw up distinct mountains of sand, coral, tiny sea animals and mud on nearby lands. The features are called chevrons because they have that form and can be found in many places on Earth.
A series of chevrons in Madagascar were piled up 205 meters (more than 670 feet) and extended 45 kilometers (30 miles) inland. That estimate comes from the Holocene Impact Working Group, which describes itself as a consortium of researchers and research groups from several countries. The tips of the chevrons point in the direction of the suspected ocean impact. In this case, the group identified the source as the Burckle Crater in the southern Indian Ocean where research revealed a 29-kilometer (18-mile) diameter structure.
That impact and ensuing tsunami about 5,000 years ago must have had devastating effects on developing human civilizations in what is now Africa, India, Arabia, Malaysia and Indonesia.
The Holocene Group also said that an impact into the Canadian glaciers 13,000 years ago may have thrown the world back into centuries of chilly conditions, known as the Younger Dryas. There also was a meteor strike in New Zealand that may have created the Little Ice Age around 1450 A.D., the group said.
The best known of all the meteor strikes is the Chicxulub impact in present-day Yucatan, which is credited with ending the age of dinosaurs 65 million years ago. The crater is estimated to be 180 kilometers (112 miles) in diameter. There was a second impact a bit later in the Ukraine that may have been a contributing factor.
NASA’s Jet Propulsion Laboratory at the California Institute of Technology maintains the Center for Near Earth Object Studies. The organization also has assembled a planetary defense committee to study ways to deflect a threatening object. The center reported that 22 space rocks with diameters between .77 kilometers (2,439 feet) and just 4 meters (13 feet) will make close approaches of less than 4.6 million miles in the next 60 days. The data is available online.
Underestimating the impact of a comet or meteor strike is easy. The truth is that they are devastating. The Tunguska event in 1908 in unpopulated Siberia “flattening 500,000 acres of uninhabited forest, scorching the land, creating ‘glowing clouds’ and producing shock waves that were detected around the world,” according to NASA. Scientists studied the window-smashing 2013 Chelyabinsk, Russia, air burst to conclude that the impacts of these mid-size events may be less frequent than previously thought, although there is little data one way or the other.
NASA used satellite technology to detect a 22-mile (35.4-kilometer) wide and a 19-mile (30.5-kilometer) wide craters under the Greenland ice sheet in 2018 and 2019. The thick ice prevents accurate dating of the impacts, but researchers think they existed before the last glacial period.
University of Alberta researchers estimated that the meteorite impact crater near the Canadian town of Whitecourt is less than 1,100 years old. The crater is about 36 meters (118 feet) in diameter.
Elon Musk, the space pioneer, published a tweet saying that “a big rock will hit Earth eventually & we have no defense.” He made the comment at the time in 2018 that NASA revealed that an asteroid named Apophis would come within 19,000 miles of the Earth within the next 10 years. Musk also has said that humans must become interplanetary species to ensure survival.
The government is taking the first baby step to protect the planet.
Musk’s SpaceX Falcon 9 will be used by NASA and a host of other agencies in a test sometime in the fall to crash a small spacecraft into one of the twin Didymos asteroids. The smaller asteroid, the target, is 160 meters (525 feet) in diameter. NASA said it estimated that the crash of the spacecraft will change the asteroid’s trajectory by about 1 percent as it rotates around its bigger brother. The collision is expected to take place when the asteroids are 11 million miles from Earth.
Published Aug. 23, 2021.
