Earth's only natural satellite, Moon, has been the topic of many theories for a long time. The question about Moon's origin has been extensively researched upon by a number of scientists and astronomers. Now, a group of scientists claim to have found the evidence of Moon's origin, right here on Earth.
Moon, My Muse
The beautiful whitish circular structure in the night sky known as the moon has been a topic of interest for humans. The moon has inspired a plethora of art and continues to do so. To think that the Earth has her very own personal companion is almost adorable. Moon is referred to as a sacred entity and is worshipped across many cultures.
As humans evolved and became more practical over the years, many theories were formulated related to the moon. One of the ridiculous ideas of all time has to be that the Apollo Moon Landing, the most historical event ever, was fake! Honestly, why would you say that? The people that accused NASA of this believed that the technology wasn’t so advanced for astronauts to go to the moon and come back safely. If the technology wasn’t so advanced back in 1969 to safely go to the moon, how could they live telecast.
Theia, The Giant Impact?
There are numerous theories about the origin of the moon. One of the theories is by George Darwin, who said that in the beginning, the Earth was spinning so fast that a part of the planet broke away and was tethered by Earth’s gravity. Another theory was that the moon originated in the Milky Way, travelled near Earth, and got trapped due to Earth’s gravity. The next theory is the Co-Accretion theory which states that Earth and moon were formed together while orbiting a black hole. The last theory is the Giant Impact Hypothesis, and the special thing about this theory is that we might have evidence supporting this hypothesis.
According to the Giant Impact Hypothesis, a Mars-sized object came in contact with a newly formed, young Earth 4.5 billion years ago. That object was named “Theia” by scientists inspired by Greek Mythology, where Theia is Selene’s mother, the moon goddess. According to this theory, Theia hit Earth, and a part of the planet chipped off and hardened into the moon. This is a better theory than the rest because this theory explains the similar chemical compositions between Earth and the moon. The ‘how’ of the similarities between Earth and Moon were unknown for a long time, but a team of scientists have proposed a theory where evidence of the moon’s creation lies within Earth.
Evidence Found Deep in Earth's Mantle
According to these scientists, Theia’s remains can be found deep within Earth’s mantle. Seismologists have been observing two blob-like structures which are found under West Africa and the Pacific Ocean. These blobs are 1000 kilometres tall and very wide. Qian Yuan, a PhD student in geodynamics, studying at Arizona State University (ASU), said, “They are the largest thing in the Earth’s mantle.”
The waves caused due to the earthquakes seems to slow down abruptly as they pass through the layers. This happens due to the layers surrounding the mantle rock are much denser and chemically different. Seismologists call these layers the Large Low-Shear Velocity Provinces (LLSVPs). They are believed to have crystallized from the depths of Earth’s primordial magma ocean. They could also be a part of the primitive mantle rock that may have survived the Moon-forming impact. Due to the new isotopic evidence, Yuan believes that these are a part of the Theia and presented this hypothesis at the Lunar and Planetary Science Conference.
Multi-Layered Protoplanet Collision Theory, the Most Probable
A geochemist named Sujoy Mukhopadhyay, from the University of California (UC), Davis, says that evidence from Iceland and Samoa suggest that LLSVPs existed since the so-called Moon-forming impact. He considers Yuan’s theory to be true but also says that it is open to other theories. Mukhopadhyay and some others have witnessed evidence that lavas on the islands contain records of radioactive elements formed at the beginning of Earth.
Yuan isn’t the only one who believed the Theia theory. ASU Tempe astrophysicist, Steven Desch who was studying the Apollo Moon rocks along with some colleagues, measured the ratios of hydrogen to deuterium. It was found that light hydrogen particles were present abundantly in the moon samples than in Earth’s rocks. In order to contain so much light hydrogen that a whole moon is formed, Theia must have been pretty big. Such a large protoplanet would have eventually separated into many layers with an iron-depleted core and an iron-rich mantle which is 2% to 2.5% denser than present-day Earth.
Deep Inside, Lies the Secret
Desch had already started modelling Theia’s fate according to the density estimated by him. His model shows that the mantle rocks were 1.5% to 3.5% denser than Earth’s and ended up as piles near Earth’s core. This Theia theory also explains the amount of LLSVPs, that contains six times more mass than the moon. Yuan said that only an impactor as massive as Theia could have delivered these rocks.
Many more remnants like that of Theia may lie deep in Earth’s mantle. Seismologists frequently find small, ultra-dense pockets of material in the Earth’s mantle, about a hundred kilometres near the edges of LLVPs. Jennifer Jenkins, a seismologist at Durham University, says that there may be other remnants of iron-rich cores from several other protoplanets that may have hit Earth in her early days.