It is estimated that on Earth About 17,000 meteorites fall a year. However, some break down into unrecoverable fragments and others are mistaken for ordinary rocks. Many may be abandoned at the back of some closet. In fact, to date, only 80,000 meteorites have been located worldwide. But if finding meteorites is complicated, finding their impact craters is much more difficult. The figures speak for themselves. Today, only 196 of these structures have been documented.
In Spain, for example, none had been found until very recently. There were two footprints suspected of having been left by a meteorite, one in Azuaranear Zaragoza, and another in the Tabernas basin, between the Almeria towns of Alhama de Almería and Alhabia. The first has been deflating as it has been investigated, but the second has finally been recognized as such by the international scientific community. It’s now official: the first meteorite impact crater has been found in Spain.
It wasn’t an earthquake, it was a meteorite. The discovery and description of this crater is the result of research carried out by the University of Almería, the Astrobiology Center and the National Institute of Aerospace Technology (INTA). It all started in 2005, when two scientists from the University of Almería, Juan Antonio Sánchez Garrido and Sebastián Sánchez, set out to study Fat Megabeda much studied rock, which for many years was considered to have seismic origin. However, they found some characteristics that did not fit with what is known as an earthquake.
There was an anomaly with platinum group elements, such as iridium, which has been located in many impact craters of meteorites detected in other parts of the Earth and even on other planets. They also tried to search shocked quartz. That is, a form of quartz that, when observed under a microscope, shows a structure displaced along crystallographic planes. It is something that can only happen at exorbitantly high pressures, such as those generated by the impact of a meteorite. Suspicions were becoming clearer. The Gordo Megabed was formed by a seismic movement, it is true, but said movement was caused by a meteorite impacting our planet.
The tests continue. Since that discovery was made, the area has been and continues to be excavated and this possible impact crater analyzed. Thus, they have also been found shatter conesknown in Spanish as splintered cones. These are striated and conical fracture surfaces found in rocks that have undergone very high pressure. This pressure is only related to the impact of a meteorite or a nuclear explosion. Since the calculations carried out indicate that this structure is 8 million years old, a nuclear explosion is ruled out.
Rock cores extracted in the excavation
But that’s not all. Magnetic evidence has also been detected. When a rock is subjected to very high temperatures, it acquires something known as a negative magnetic anomaly. With the impact of a large meteorite, great pressure is generated, which in turn gives rise to an enormous increase in temperature. They can reach more than 2,000ºC. Therefore, it is more than normal for these anomalies to be detected, the monitoring of which has allowed the crater to be delimited in the case of Almería. Or, at least, it allowed us to define where the crater was suspected to be.
The Swedes enter the scene. The fact that an impact crater has never been detected in Spain means that Spanish scientists are logically not familiar with this type of anomaly in the rock. For this reason, these scientists from the University of Almería partnered with the rest of the aforementioned institutions, but they also consulted Swedish researchers.
In Nordic countries, such as Sweden, Norway and Finland, there are older geological materials, in which several impact craters have been detected. When these scientists joined the investigation, they confirmed the suspicions that had gradually taken over Spanish scientists. They had found the impact crater of a meteorite. The first in Spain.
The characteristics of the crater. When we think of a crater we imagine it as a hole clearly drilled into the Earth. Like the typical craters of the Moon. However, we must keep in mind that on Earth there are winds and geological movements, absent on our satellite, that do not leave the craters visible over the years. What these scientists have found is close to the surface in some points, but in others it is buried with a sediment pressure of 800, 900 and even 1,000 meters.
Even so, with all of the above, we know that it is a crater with a radius of 5 kilometers, along with a fragmented area that reaches a radius of 24 kilometers. That is, in a way we have the “hole” left by the meteorite and, around it, all the ground that is fractured as a result of the impact. The very edges of the crater are what we see today as mountains. In the video below it can be seen perfectly.
And what about the meteorite? There are very well-studied impact craters that have made it possible to calculate the relationship between the size of a meteorite and the radius of the crater it leaves. Taking this and some other factors into account, it is estimated that the meteorite must have measured around 800 meters. All this is what is known so far.
The excavations are not over yet. Rock cores are being extracted with them. That is, cylinders of material excavated for subsequent analysis. With this they hope to find even more crushed quartz and new evidence that will allow them to describe more concisely what happened in that area of the Tabernas desert, then submerged under the sea, when a huge meteorite hit it 8 million years ago.
Images | SEA
GIPHY App Key not set. Please check settings