Scientists have uncovered evidence that Earth’s building blocks may come from a single region of the Solar System, overturning assumptions about widespread material mixing.
Credit: Stock
Planetary scientists have long debated the origin of the material that formed Earth. Although our planet sits in the inner Solar System, many researchers have estimated that between 6 and 40 percent of its building material came from beyond Jupiter in the outer Solar System.
For years, scientists believed that outer Solar System material was needed to deliver volatile substances such as water. This idea implied that material must have moved between the outer and inner regions while Earth was forming. But new research is now questioning that assumption.
But is that really true?
“We were truly astonished”
Paolo Sossi and Dan Bower of ETH Zurich compared isotopic data from a wide range of meteorites, including samples linked to Mars and the asteroid Vesta, with Earth’s composition. Isotopes are atoms of the same element that share the same number of protons but differ in mass because they contain different numbers of neutrons.
Using a new analytical approach, the team reached an unexpected conclusion. Earth appears to have formed entirely from material that originated in the inner Solar System.
Material from beyond Jupiter likely makes up less than 2 percent of Earth’s mass, and may not have contributed at all. The findings were published in Nature Astronomy.
Credit: ESO/C. Lawlor, R. F. van Capelleveen et al.
“Our calculations make it clear: the building material of the Earth originates from a single material reservoir,” says Sossi. His colleague Bower adds: “We were truly astonished to find that the Earth is composed entirely of material from the inner Solar System distinct from any combination of existing meteorites.”
To reach this result, the researchers analyzed data from ten different isotopic systems found in meteorites and applied a statistical method not commonly used in geochemistry. Earlier studies typically relied on only two isotopic systems.
“Our studies are actually data science experiments,” says Sossi. “We carried out statistical calculations that are rarely used in geochemistry, even though they are a powerful tool.”
Isotope signature reveals origin
Scientists have long used isotopes in meteorites to identify where celestial materials formed within the Solar System. In the past, this work focused mainly on oxygen isotopes.
In the early 2010s, researchers showed that isotopes of elements such as chromium and titanium could also reveal origins. This led to a classification system that separates meteorites into two groups. Non-carbonaceous meteorites formed in the inner Solar System, while carbonaceous meteorites, which contain more water and carbon, originated farther out.
The new study shows that Earth is made entirely of non-carbonaceous material. It also finds no evidence of the previously proposed mixing between inner and outer Solar System reservoirs.
This suggests that Earth formed in a relatively stable environment, gradually growing by accreting nearby planetary material. It also indicates that volatile elements such as water were likely already present in the inner Solar System.
“Our calculations make it clear: the building material of the Earth originates from a single material reservoir,” says Sossi. His colleague Bower adds: “We were truly astonished to find that the Earth is composed entirely of material from the inner Solar System distinct from any combination of existing meteorites.”
To reach this result, the researchers analyzed data from ten different isotopic systems found in meteorites and applied a statistical method not commonly used in geochemistry. Earlier studies typically relied on only two isotopic systems.
“Our studies are actually data science experiments,” says Sossi. “We carried out statistical calculations that are rarely used in geochemistry, even though they are a powerful tool.”
Isotope signature reveals origin
Scientists have long used isotopes in meteorites to identify where celestial materials formed within the Solar System. In the past, this work focused mainly on oxygen isotopes.
In the early 2010s, researchers showed that isotopes of elements such as chromium and titanium could also reveal origins. This led to a classification system that separates meteorites into two groups. Non-carbonaceous meteorites formed in the inner Solar System, while carbonaceous meteorites, which contain more water and carbon, originated farther out.
The new study shows that Earth is made entirely of non-carbonaceous material. It also finds no evidence of the previously proposed mixing between inner and outer Solar System reservoirs.
This suggests that Earth formed in a relatively stable environment, gradually growing by accreting nearby planetary material. It also indicates that volatile elements such as water were likely already present in the inner Solar System.
Jupiter acts as a material barrier
But why are there two distinct material reservoirs in our Solar System?
Scientists think the Solar System split into two distinct regions early in its history because of Jupiter’s rapid formation. As the gas giant grew, its gravity carved a gap in the protoplanetary disc surrounding the young Sun. These discs are rings of gas and dust where planets form.
Jupiter likely blocked most material from the outer Solar System from moving inward, though how effective this barrier was has been uncertain.
The new analysis indicates that almost no material from beyond Jupiter reached Earth. “Our calculations are very robust and rely solely on the data itself, not on physical assumptions, as these are not yet fully understood,” Bower emphasizes. The results also show that Earth’s composition closely matches that of Mars and Vesta.
The team suggests that Venus and Mercury may share a similar composition. “Based on our analysis, we can theoretically predict the composition of these two planets,” says Sossi. However, this cannot yet be confirmed because no rock samples from these planets are available.
New light on the formation history
“Our results shed new light on the formation history of our Earth and the other rocky planets,” says Sossi.
The researchers plan to investigate how enough water existed in the hot inner Solar System to form Earth’s oceans. They also want to explore whether similar processes occur in planetary systems beyond our own.
“Until then, however, Dan and I will have to engage in many heated debates about the material composition of Earth and its neighboring planets, because the scientific discourse over the building blocks of Earth is far from over, despite the new findings,” says Sossi.
The Life of Earth
https://chuckincardinal.blogspot.com/
astronomy is so full of assumptions sold as facts.
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