a fact or situation that is observed to exist or happen, especially one whose cause or explanation is in question.

Stones of Ica

Thousands of stones with engravings depicting complex surgeries, dinosaurs and even space travel have been discovered in the Peruvian city of Ica. These stones, known as the Ica stones, raise many questions for researchers.

The collection has more than 50,000 stones of various sizes. Some of them, some researchers claim, could be as old as 65 million years. However, official science is skeptical about these data.

According to research conducted in the 1960s, about 30 per cent of the images on the stones do not match known historical and palaeontological data. This has given rise to many theories about the origin of the stones, including hypotheses about ancient highly developed civilizations and even extraterrestrial intervention.

Klerksdorp spheres

Hundreds of metallic spheres known as Klerksdorp spheres have been discovered in pyrophyllite mines in South Africa. These objects, which date back about 2.8 billion years, are perfectly round in shape and have parallel grooves on the surface.

In total, about 200 spheres have been found, ranging from 2.5 to 10 centimeters in diameter. Some are made of solid bluish metal with white spots, while others are hollow and filled with a spongy substance.

Analyses have shown that the spheres are composed of pyrite (FeS2) with impurities of other minerals. However, their perfectly round shape and parallel furrows cannot be explained by known geological processes. Some researchers suggest that these objects may be the result of an ancient civilization or even of extraterrestrial origin.

Ball lightning

Ball lightning is a rare and mysterious atmospheric phenomenon observed as luminous spheres floating in the air. Despite numerous eyewitness accounts, scientists still cannot fully explain the nature of this phenomenon.

According to research, ball lightning is observed in about 5% of thunderstorm activity. Their diameter usually varies from 10 to 40 centimeters and their time of existence from a few seconds to a few minutes.

A survey of 1,600 scientists found that 5% of them had personally observed ball lightning. Despite this, it has not yet been possible to create stable ball lightning in laboratory conditions, which makes them difficult to study.

The Tunguska meteorite phenomenon

On 30 June 1908, a powerful explosion known as the Tunguska phenomenon occurred in Siberia. The explosion felled trees over an area of about 2,150 square kilometers and was heard up to 800 kilometers away.

The power of the explosion is estimated at 10-15 megatons in TNT equivalent, which is comparable to the power of a large hydrogen bomb. However, despite the force of the explosion, no crater or meteorite fragments have been found.

In more than 100 years of research, more than 120 hypotheses have been put forward about the nature of the Tunguska phenomenon, including a comet impact, a UFO explosion and Nikola Tesla's experiments. However, none of these theories has been definitively confirmed.

The mystery of the Pyramid of Cheops

The Great Pyramid of Giza, also known as the Pyramid of Cheops, continues to baffle researchers with its precision and complexity of construction. Built about 4,500 years ago, it remains one of the most precisely orientated structures on Earth.

The pyramid consists of approximately 2.3 million stone blocks, each weighing between 2.5 and 15 tones. The total weight of the pyramid is estimated at 5.9 million tones. Thus accuracy of masonry is amazing: gaps between blocks do not exceed 0,5 millimeters.

Orientation of the pyramid on the sides of the world is so exact that deviation makes less than 0,06 degrees. This level of precision is difficult to achieve even with modern technology, let alone ancient construction methods.

Voynich Manuscript

The Voynich Manuscript is an illustrated codex written by an unknown author in an unknown language using an unknown alphabet. Dating back to the 15th century, it has not yet been deciphered, despite numerous attempts by cryptographers and linguists.

The manuscript contains some 240 pages filled with text and strange illustrations of plants, astronomical diagrams and nude female figures. Analyses of ink and parchment have confirmed its authenticity and age.

Statistical analysis of the text shows that it has linguistic properties typical of real languages. However, despite the use of modern cryptanalysis and machine learning techniques, the content of the manuscript remains a mystery.

London Hammer

In 1934, a hammer encased in a rock some 400 million years old was discovered in Texas. This artefact, known as the Hammer of London, challenged traditional ideas about the development of human civilization.

Metallographic analysis revealed that the hammer is composed of 96.6 per cent iron, 2.6 per cent chlorine and 0.74 per cent Sulphur. Such a composition is uncharacteristic for modern metal products and testifies to the high level of metallurgical technology.

Over the years of research, more than 10 hypotheses about the origin of the hammer have been put forward, but none of them has received final confirmation. Some scientists suggest that the hammer could have been made in the XIX century and accidentally found in older rocks, but this theory does not explain the unusual composition of the metal.

Phenomenon of crystal transposition

Strange inclusions have been found in some quartz crystals that appear to have moved within the crystal after it was formed. This phenomenon, known as crystal transposition, contradicts the known laws of crystallography.

Studies have shown that some inclusions in quartz crystals, such as rutile or tourmaline, are in positions they could not have occupied during the natural growth of the crystal. In some cases, these inclusions even cross the boundaries between the different growth zones of the crystal.

This phenomenon is observed in about 1 in 10,000 quartz crystals. Despite numerous studies, scientists are still unable to explain the mechanism that allows solid inclusions to move within a solid crystal.

The phenomenon of mass extinctions

There have been several periods of mass extinctions in Earth's history, the most famous of which is the extinction of the dinosaurs 66 million years ago. However, the causes of some other mass extinction periods remain a mystery to scientists.

According to paleontologists, there have been five major and about 20 smaller mass extinction periods in the last 500 million years. During the largest of these, the Permian extinction, about 95 per cent of all marine species and 70 per cent of terrestrial vertebrates disappeared.

Studies show that major species extinctions occur every 26-30 million years on Earth. This periodicity has given rise to the hypothesis that there is an external factor, possibly of cosmic origin, affecting the Earth's biosphere.

Deja vu phenomenon

Deja vu is a psychological phenomenon in which a person experiences the sensation that a current situation has already occurred in the past. Despite numerous studies, the exact mechanism of deja vu remains unknown.

According to surveys, about 70% of people have experienced deja vu at least once in their lives. At the same time, the frequency of this phenomenon decreases with age: if among people under 30 years old, déjà vu is experienced by about 80%, then after 60 years - only 20%.

Neurophysiological studies show that during déjà vu the brain areas associated with memory and perception of novelty are activated. However, scientists are still unable to explain why this happens and what the significance of this phenomenon is.

Nazca Lines

Peru's Nazca Desert is home to giant geoglyphs known as the Nazca Lines. These depictions of animals, plants and geometric figures, created between 500 BC and AD 500, are only visible from a great height.

The total area covered by the Nazca lines is about 1,000 square kilometers. Some figures reach 300 meters in length. The accuracy of the lines is amazing - the deviation from a straight line does not exceed a few centimeters for kilometers.

Bog people

Well-preserved bodies of people who lived thousands of years ago are periodically found in peat bogs in northern Europe. These finds, known as ‘bog people,’ provide unique information about the lives of ancient people, but also raise many questions.

To date, about 1,000 bog people have been discovered. Some finds are as old as 10,000 years, although most date from between 800 BC and 400 AD.

Analyses of the remains show that many bog people died violent deaths. About 40 per cent of the bodies show signs of ritual murder or execution. This has given rise to theories about human sacrifice and the complex religious practices of the ancient peoples of Europe.

Aerial photography conducted in the 1940s revealed more than 300 different figures. Since then, about 900 more geoglyphs have been discovered. The purpose of these lines remains a matter of debate among scientists. Theories range from astronomical calendars to ritual roads and even runways for alien ships.