There are only three craters in China, which is 9.6 million square kilometers, how was it discovered

Our earth has been constantly visited by "aliens" since its birth. And the traces left on the earth by these "aliens" are craters.

In fact, just before the 21st century, our country had not discovered a single crater. However, in the past decade, the number of craters discovered in China has jumped from 0 to 3.

Just recently, Chen Ming's team, a researcher at the Beijing High Voltage Science Research Center, discovered a crater with a very peculiar shape and occurrence in Tonghua City, Jilin Province - Baijifeng Crater. This is the third crater in our country and the first alpine crater in the world. The results were published in the journal "Matter and Radiation under Extreme Conditions".

Baijifeng crater photographed by drone (Image source: Chen Ming's research team)

The mysterious "White Rooster Peak"

The site of the crater's discovery, Baijifeng National Forest Park, is located in the southeast of Dongchang District, Tonghua City, Jilin Province, with a total area of 1,041 hectares and a forest coverage rate of 98.7%, which is a forest eco-tourism scenic spot dominated by natural landscapes.

Baijifeng National Forest Park is named after the two peaks in the park: the former Baiji Peak and the back Baiji Peak. The summits and slopes of these two mountains are covered with off-white rock fragments of different sizes, forming a stone waterfall with an area of tens of thousands of square meters, which is breathtaking. However, how these "heavenly stones" were formed is always an unsolved mystery.

The "sky stone" on the top of Baiji Peak

However, with the discovery of Baijifeng Crater, the mystery of "Tianshi" was gradually revealed.

According to research published by Chen Ming's team in the journal "Matter and Radiation under Extreme Conditions", about tens of thousands of years ago, an asteroid with a diameter of tens of meters hit the top of Baijifeng Mountain at cosmic speed, causing huge explosions and rock ejections, forming a huge impact crater and changing the original shape of the mountain.

After investigation, they found that Baijifeng is mainly composed of bedrock materials such as Proterozoic sedimentary rocks and Jurassic granite, and the stone waterfalls now distributed on the top and slopes are the accumulation products of quartz sandstone and granite and other rock fragments ejected from the crater to the edge of the crater during the asteroid impact. This discovery solved the mystery of the cause of Baiji Peak's "Tianshi".

A rare crater on Earth

The total area of the earth is about 510.072 million square kilometers, of which the land area is about 148.94 million square kilometers. Some people may think that there must be many craters on the earth with such a vast geographical area, but in fact there are only more than 200 craters found on the earth so far.

Distribution of large craters currently discovered on Earth (incomplete statistics)

Although the Earth and the Moon belong to the same Earth-Moon system and should have suffered similar frequencies of strong impacts in history, there are now 300,000 craters on the moon of more than 1 kilometer, so why are there only more than 200 craters on Earth?

In fact, this is closely related to the geological activities that the earth has undergone since its formation.

In the 4.6 billion years since the formation of the earth, strong geological activities have caused plate tectonic movements, orogenies, volcanic eruptions, glacial movements, etc. on the earth's surface, in addition, there are our common weathering and denudation phenomena, depressions and sedimentary burial, which can cause the craters formed on the earth's surface to be destroyed, eroded, or even buried.

So where are the three craters in China concentrated?

The answer is the three eastern provinces.

In addition to the Baijifeng crater mentioned above, the other two, one is Xiuyan Crater in Anshan City, Liaoning Province, with a diameter of about 1.8 kilometers.

Top view of Xiuyan Crater at an altitude of 800 meters (Image source: People's Daily Online)

The other is the Ylang Crater in Yilan County, Harbin City, Heilongjiang Province, with a diameter of about 1.85 kilometers.

Panorama of the ylang-ylang impact crater taken by a drone at an altitude of 500 meters

These three craters were all discovered by Chen Ming's team.

So how to determine which places are craters? At present, the only way is to search for stones all over the mountains, find those stones that have been strongly impacted, and then use electron microscopy and other methods to find some evidence of mineral physical and chemical changes caused by shock waves.

The first is ultra-high pressure minerals. This mineral is only possible more than a few hundred kilometers deep in the earth. If it appears on the surface, it means that the surface has been subjected to high pressure. Therefore, ultra-high pressure minerals are an important basis for identifying craters.

The second is the surface deformation sheet texture produced by the special deformation of minerals. This page texture is very special, like a knife cut, this phenomenon cannot be found on ordinary earth rocks, only shock waves can cause this phenomenon.

The third is the vitrification of mineral crystals. The shock wave can cause the atomic dot matrix in the crystal to be disrupted in an instant, and the shape of the mineral can be preserved, but the inside has become vitreous, and this "destruction glass" is closely related to meteorites.

The above three criteria are the three types of diagnostic evidence for the international scientific community to judge craters, as long as one of them can be found, it can be sure that it is a crater.

So, why do we study craters?

In fact, the study of Earth's craters can not only help or promote the exploration of our extraterrestrial planets and understand the history of extraterrestrial planets, but also help us discover special mineral resources, such as the world's largest gold minerals, the largest nickel minerals, and the largest diamond minerals in the craters. So in general, crater research is of great significance.

So, how much room is left for crater excavation in China?

In fact, for now, the density of impact craters found per unit of land area in China is much lower than the world average, which means that there are more "hidden" impact craters that have not yet been discovered and confirmed. Perhaps with the continuous exploration of scientists, more craters will be excavated in the near future and bring us new "surprises".