6 Fascinating Earth Mysteries Scientists Still Can't Explain

Have you ever wondered about the mysteries hidden beneath the surface of our planet? Questions like why some trees grow in gigantic rings, what causes unusual atmospheric tremors, or where the Mediterranean Sea disappeared to millions of years ago remain unanswered.

1. The Enigma of Gigantic Tree Rings

Across vast forests in Australia, Canada, and Russia, trees sometimes arrange themselves into massive circular patterns. These rings—up to 90 meters wide and spanning nearly two kilometers in diameter—are invisible at ground level but strikingly clear in aerial photographs. Scientists estimate that there are at least 8,000 such natural formations worldwide.

Despite intensive research, the reason behind this peculiar circular tree growth remains a mystery. Unlike crop circles explained by human activity, no clear evidence suggests these patterns are man-made.

Several theories exist. Canadian researchers initially suspected large fungal colonies at the roots might cause tree death in circles, but this was disproved. Another possibility is that soil bacteria alter acidity in a way that suppresses tree growth in ring shapes.

Other hypotheses propose underground geological features like kimberlite pipes or gas pockets influencing growth patterns, or even ancient meteorite impacts leaving their mark. However, none have been definitively proven.

2. The Phenomenon of Skyquakes

Earthquakes produce familiar rumbles beneath our feet, but sometimes an eerie, thunderous noise originates from the sky. This phenomenon, called “skyquake,” has been reported in countries such as Japan, Russia, India, Ireland, England, Norway, the Netherlands, Argentina, Brazil, Indonesia, Italy, and many more.

In Japan, it's known as "uminari," meaning "sea roar," though these sounds often occur far from any ocean. The sky emits a distant but powerful booming sound without any lightning, storms, or clouds present.

The cause remains elusive. Scientists speculate it could be related to solar coronal mass ejections interacting with Earth's upper atmosphere, meteorite entries, magnetic activity resonance, volcanic eruptions, avalanches, gas emissions from underground caves, or unique atmospheric acoustics amplifying distant thunder.

However, no conclusive explanation has yet emerged.

3. Origins of Earth's Water

Earth is unique among planets in our solar system for having about 70% of its surface covered by liquid water oceans. While other celestial bodies contain water, none hold such vast quantities. The origin of Earth's abundant water remains a subject of debate.

Many scientists believe that shortly after Earth formed roughly 4.6 billion years ago, it was as dry as Mercury. During the period known as the Late Heavy Bombardment, between 4.1 and 3.8 billion years ago, numerous asteroids collided with Earth, delivering large amounts of ice that eventually formed the oceans.

Others suggest Earth's water largely arrived from a colossal impact with a protoplanet named Theia, which also led to the Moon’s formation.

Another theory posits that water was present during Earth's formation from the protoplanetary disk of gas and dust orbiting the young Sun, supported by evidence of significant water trapped deep within Earth's crust and traces found in lunar soil samples matching Earth's isotopic signatures.

A particularly intriguing hypothesis claims some of Earth's water came directly from the Sun in the form of water vapor carried by solar winds, especially from sunspot regions where water vapor is abundant, as suggested by researchers at the University of Glasgow.

Despite these theories, astrophysicists still lack definitive data to pinpoint the exact origin of Earth's oceans.

4. The Mystery of Meat Rain

On March 3, 1876, in Bath County, Kentucky, USA, several pieces of meat reportedly fell from the sky between 11 a.m. and noon. Witnesses, including a local farmer's wife, considered it a divine sign.

Scientists from Transylvania University collected samples, some of which were even tasted, with descriptions ranging from lamb to venison, while a local hunter claimed the meat was from a bear.

Further scientific analysis indicated the samples contained cartilage, muscle tissue, and lung material possibly from a foal or—astonishingly—a human infant, whose lung structure resembles that of a horse.

Similar incidents were recorded in Europe, such as in London on March 12, 1876, where fragments resembling veal also fell.

While various objects have been reported to fall from the sky—including frogs, fish, and even tennis balls—the most common explanation involves tornadoes lifting and transporting objects. Yet, it’s hard to imagine a tornado dismembering large animals before lifting them.

Two main theories attempt to explain the Kentucky meat rain: one suggests the meat was actually colonies of Nostoc—cyanobacteria that inhabit oceans and can be lifted into the atmosphere by typhoons, resembling unappetizing chunks of cartilage.

Another proposes that a passing vulture might have vomited mid-flight due to stress-induced airsickness. Nevertheless, the true cause remains unknown.

5. Could Earth's Ancient Oceans Have Been Purple?

From space, Earth is predominantly blue, green, and white. However, scientists propose that billions of years ago, the planet's oceans may have displayed different colors.

Chlorophyll, the pigment responsible for photosynthesis in plants and algae, is green. But genetic microbiologists from the University of Maryland suggest that around 2.3 billion years ago, Earth's earliest photosynthetic cells might have relied on retinal, a purple or pink pigment more efficient than chlorophyll.

Retinal is also found in the eyes of vertebrates, including humans, where it helps convert light into metabolic energy for vision.

Purple retinal pigments are used by halophilic archaea like halobacteria, some of Earth's most ancient life forms that thrived before oxygen was abundant.

This "Purple Earth" theory speculates that early photosynthetic life resembled these archaea rather than modern green algae. Eventually, green cyanobacteria outcompeted the purple predecessors, becoming dominant. However, fossil evidence for two-billion-year-old bacteria is scarce, making the theory difficult to confirm.

If true, Earth's ancient oceans may have looked like the pink Lake Hillier near Australia’s coast.

6. The Disappearance and Return of the Mediterranean Sea

Approximately 5.96 million years ago during the Miocene epoch, the Mediterranean Sea dried up entirely, transforming into a vast barren valley between 3 and 5 kilometers deep, with only a few small saline lakes remaining. This event is known as the Messinian Salinity Crisis.

Today, thick salt deposits remain on the sea floor—research vessels have found salt layers up to two kilometers thick, a testament to this dramatic event.

The conditions at the time were harsh: extremely salty soils inhospitable to life except for hardy extremophile bacteria, very dry climate, and temperatures soaring up to 80°C—making today's Death Valley seem mild by comparison.

The exact cause of the crisis remains unclear. Possible explanations include tectonic shifts or unusual climate changes. The closure of the Strait of Gibraltar cut off Atlantic water, leading to the sea's evaporation. Some evidence also suggests the Red Sea may have dried out during this time.

About 5.33 million years ago, the Mediterranean gradually refilled through the reopening of the Gibraltar Strait, regaining its modern shape. However, geologists warn the sea could dry up again in the future due to its high salinity causing rapid evaporation and the northward movement of the African tectonic plate.

Eventually, in about a thousand years, a new mountain range may rise where the sea currently lies. So, if you plan to visit the Mediterranean, now is the time!

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