Huge rocks from space or asteroids fall from the sky more than before. But there is nothing to worry about.
A recent study has shown that large asteroids have crashed twice on earth in the last 290 million years, more than 1945,9005 (1945,9006), as often as in the 700 million years before. The journal Science published the study in January.
But even with the increased crash rate, asteroids still hit Earth every million or a few million years.
The United States Space Agency (NASA) lists their observation of large space rocks that could plunge into the earth. There are no big threats coming soon.
The biggest known risk is a 1
University of Toronto scientist Sara Mazrouei led the study. She told the Associated Press that she was not worried about asteroids hitting the earth because of such rare events.
"It's just a game of probabilities ," she said.
Mazrouei collaborated with British researchers and the US on the study. Together, they collected a list of the major brands that leave asteroids on planets and other objects, also known as impact craters.
The researchers studied impact craters on Earth and their lunar that were larger than 20 kilometers. To create such a large hole requires a 800 meter wide space rock.
They also appreciate the data of the craters. The team counted 29 craters less than 290 million years old. And they found nine between 291 million and 650 million years ago.
Rebecca Ghent, another University of Toronto scholar, also joined the study. She found that we can see relatively few large craters on the Earth's surface, as the planet is over 70 percent oceanic. The movement of large icebergs, also known as glaciers, covered some of them.
The team estimated that there were 260 accidents on Earth over the past 290 million years. And this crash rate is 2.6 times higher than 700 million years ago.
Because glaciers covered mostly older craters, scientists studied craters on the moon to estimate the age of humans on Earth between 650 million and 1 billion years. The Moon is close enough to Earth to be on the same path as the asteroids, and its craters last longer.
So what happened almost 300 million years ago?
"Perhaps an asteroid family was broken in the asteroid Belt ," suggested Mazrouei. The space rocks then headed for the earth and the moon, Gent added. The planet then got a few more hits because it's a bigger target and higher gravity.
Other scientists are split as far as the research teams of the team are concerned. Earth scientist Jay Melosh of Purdue University said he finds the number of craters too small to prove an important point. However, Harvard University's Avi Loeb agreed with the team's results.
Modern man could not have existed without the massive extinctions of space rock, wrote Loeb in an e-mail. Most scientists believe that dinosaurs and many other animals are extinct after a huge space rock crashed in Central America 65 million years ago.
"This shows how is arbitrarily and human Life is," he wrote.
I am Pete Musto.
Seth Borenstein has reported this story to the Associated Press Pete Musto adapted it for VOA learning English Hai Do was the publisher We want to hear from you How concerned are you about a crashed asteroid? Write us in the comment section or on our Facebook page  ______________________________________________________________
Words in this story
– – adv. Doubles in amount or degree
Journal – n. a journal reporting on matters of particular interest to a particular group of people
Probabilities – n. the Chances that something will happen
Belt – n. a region that has a lot of special
extinction ( s ) – n. the state or situation that arises when something, such as a plant or animal species, is completely extinct
arbitrarily not planned for any reason or selected
fragile – easily broken or damaged