14 DAY TRIAL // A paper published in the February 16 issue of the top journal Science suggests that some of the rocks on our planet were extremely slow to change and undergo recycling. These data are now added to a growing body of gaps in our knowledge of how early Earth evolved.
According to the investigation, some of the most sluggish rocks took in excess of 1.5 billion years to reenter the mantle, and then melt into a viscous form. This process occurs naturally, as tectonic plates undergo a process called subduction.
The latter occurs at the boundaries of colliding tectonic plates. One of them moves underneath the other, and is melted under the extreme heat of the mantle. The rocks making it up are liquefied, and eventually make their way back to the surface via rifts in the ocean.
What the new study suggests is that some of the rocks that made their way into the mantle took a very long time to undergo this process, even though they were subjected to intense heat and pressures.
One of the main implications of the research is that Earth's interior is not such a well-mixed system as geologists first thought. Rather, the mantle, and the material it contains, look like a heterogeneous system, Space reports.
The investigation was carried out on volcanic rocks collected from Russia (2.82 billion years old) and South Africa (3.47 billion years old). Fully understanding our planet's geological history may never be possible, due to the fact that no rocks are left from the time it formed, nearly 4.5 billion years ago.
After analyzing the isotopic signature of the various samples, the University of Maryland research team arrived at some interesting conclusions.
“This difference in isotopic composition requires that the Earth formed and separated into a metallic core, silicate mantle, and perhaps crust, well within the first 60 million years of solar system history. In itself this is not new or surprising,” geochemist Mathieu Touboul says.
“What is new and surprising is that a portion of the growing Earth developed the unusual chemical characteristics that could lead to the enrichment in tungsten-182, and also that this portion of the mantle remained distinct from the rest of the mantle for more than 1.5 billion years,” he goes on to say.
The group believes that this portion of the mantle contributed some of the material that makes up the rocks researchers analyzed. What this implies is that the earliest portions of our planet formed just 10 to 20 million years after the solar system coalesced.
“These earliest building blocks for the planet remained distinct until at least 2.8 billion years ago,” Touboul concludes.