The world's biggest explosion - a blast in Russia the size of 185 Hiroshima bombs that was felt as far away as Britain and the US - remains a mystery after experts debunked 'proof' it was a meteorite.

A large fireball was seen crossing the Siberian sky on June 20, 1908 before an eruption six miles above ground flattened 80 million trees and left charred reindeer carcases.

Italian scientists spent 21 years researching the so-called Tunguska event, claiming the blue-water Lake Cheko filled a 'missing' impact crater - giving rise to the theory that the phenomenon was caused by a meteorite.

But a new study by Russian geologists suggests the idea is flawed, meaning the huge blast - which lit up the night sky in Europe and even America - is still a mystery, according to reports in Moscow.

While they have not put forward an alternative explanation for the explosion, outlandish theories in the past have included a massive volcanic eruption, a comet mainly composed of ice not solid space rock, a black hole colliding with Earth and even aliens shooting down a meteor from a UFO in order to save Earth.

Local Evanki people believed it was a visitation by an angry god called Ogdy.

The world's biggest explosion in Russia in 1908 was initially thought to have been the result of a meteorite that created Lake Cheko (pictured) in Siberia

A large fireball was seen crossing the Siberian sky on June 20, 1908 before an eruption six miles above ground flattened 80 million trees and left charred reindeer carcases

A study by Russian geologists (pictured) suggests early theories about the explosion are flawed, meaning the huge blast - which lit up the night sky in Europe and even America - is still a mystery, according to reports in Moscow

There were reports at the time that the blast was felt as far away as Britain while the explosion lit up the sky in the US

The biggest-ever documented explosion was the size of 185 Hiroshima nuclear bombs - yet there was no evidence of human fatalities.

'There was a bang in the sky and a mighty crash. The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled,' said a native Siberian some 40 miles from the epicentre.

It appeared to be Armageddon. 'I became so hot I couldn't bear it, as if my shirt was on fire,' said another account.

'I wanted to tear off my shirt and throw it down, and then the sky slammed shut. A strong thump sounded and I was thrown a few yards.'

It caused shockwaves as far away as Britain and dust from the explosion lit up the night sky in its wake in Europe and even America.

From the first Soviet expeditions to this remote region of Siberia, the puzzling aspect was a lack of debris, for example craters caused by fragments of a meteorite, on the surface.

Italian scientist Luca Gasperini, from the University of Bologna, has long believed crater-shaped Lake Cheko (pictured), some five miles from the epicentre, to be the missing link in the Tunguska mystery

Italian scientist Luca Gasperini, from the University of Bologna, has long believed crater-shaped Lake Cheko, some five miles from the epicentre, to be the missing link in the Tunguska mystery.

It was not marked on tsarist-era maps of Siberia, and his team's seismic measurements of its bottom indicated sediment had been building for around a century.

They concluded that dense stony matter lies beneath the lake's floor and is the 'remnant' of the exploding meteorite.

The Italian theory based on the pattern of tree destruction is that two bodies entered the atmosphere. One exploded about five miles above ground, and the other hit the Earth forming Lake Cheko.

TUNGUSKA THEORIES: WHAT COULD HAVE 'SPLIT THE SKY IN TWO' IN 1908

More than 110 years ago, a massive explosion ripped through the sky over the Tunguska region of Siberia, flattening trees nearly 31 miles around. The blast is thought to have been produced by a comet or asteroid hurtling through Earth's atmosphere at over 33,500 miles per hour, resulting in an explosion equal to 185 Hiroshima bombs as pressure and heat rapidly increased. But, with no definitive impact crater and little evidence of such an object ever found, scientists remain perplexed as to what truly caused the event in which 'the sky was split in two'. Numerous studies have attempted to make sense of what happened on June 30, 1908 at Tunguska. The biggest-ever documented explosion was the size of 185 Hiroshima nuclear bombs - yet there was no evidence of human fatalities. Pictures show trees flattened by the blast From UFO theories to speculation about the supernatural, the mysterious event has spurred explanations of all kinds, many of them lacking scientific basis. Some scientists even suggested a black hole had collided with Earth – but other experts quickly shot down the idea. In a review published in 2016 in the Annual Review of Earth and Planetary Sciences, Natalia Artemieva of the Planetary Science Institute in Tucson, Arizona explains that the event followed a clear course. Whatever caused the event likely entered the atmosphere at 9-19 miles per second, and would have been extremely fragile, destroying itself roughly six miles above Earth. The possibility of an asteroid explosion was first proposed in 1927 by Leonid Kulik, 20 years after the event. Others suggested the space-object may instead have been a comet, made up of ice rather than rock, meaning it would have evaporated as it entered Earth's atmosphere. But, some scientists warn that these findings do not definitively explain the bizarre explosion – with meteor showers being a frequent occurrence, these samples could be the remnants of a much smaller, unnoticed event. To some degree, the Tunguska event still remains a mystery, which scientists are continually working to solve – but, whether it be from a comet or asteroid, most agree that the explosion was caused by a large cosmic body slamming into Earth's atmosphere. Advertisement

The blast led to a host of theories on the cause apart from a meteorite: from a massive volcanic eruption, to comet mainly composed of ice not solid space rock, to a black hole colliding with Earth, to aliens shooting down a meteor from a UFO in order to save Earth. Fallen trees could still be found at the site in the 1990s (pictured)

talian scientists (pictured in 1999) spent 21 years researching the so-called Tunguska event, claiming the blue-water Lake Cheko filled a 'missing' impact crater - giving rise to the theory that the phenomenon was caused by a meteorite

The explosion - the force iof 185 Hiroshima bombs - was recorded over Siberia but was felt as far away as Britain

Now Russian researchers have examined the sediment from the deepest part of the lake, some 50 metres below the surface, and undertaken geochemical and biochemical analysis.

The study indicates that the deepest sample they obtained is about 280 years old, which means that the lake is probably even older, because the researchers did not manage to obtain samples from the very bottom of the sediment layer.

'Besides, there are other deep, practically round lakes in the Tunguska reserve, which look like Lake Cheko and probably have the same geological origin,' said a statement from the expedition centre of the Russian Geographical Society in the Siberian Federal District.

According to local reports, traces of the mysterious Tunguska event can be seen even now

An aerial photograph of the Lake Cheko was obtained by an earlier Italian survey of the area

Aerial images show the pattern of trees flattened after the 1908 explosion and the inferred epicentre

'Geologically the lake appears young. But not young enough to be a crater lake caused by Tunguska,' reported The Siberian Times, which also said the reason for its formation remains a mystery.

So the puzzle over Tunguska remains, but the answer could be that it was a meteorite and that it exploded in the air.

In 2013 rock samples of meteoric origin with traces of a carbon mineral called lonsdaleite were found in this part of Siberia.

These are known to form when meteorites crash to Earth but could have been from other unrelated meteor showers.