By studying zircon crystals dating back about 3.8 billion years, scientists have gained access to record-old evidence confirming the presence of tectonic plate activity on our planet. What can you learn in this way? The isotopes and elements of such crystals provide information on the conditions under which they were formed. And the collected data suggest that it took place under subduction conditions, due to which one edge of the tectonic plate slides under the edge of the adjacent one. With this knowledge, scientists are able to determine, inter alia, the time frames in which the processes related to the origins of the Earth's tectonics occurred.
Zircon crystals like time capsules
The authors of the research on this issue presented their findings in AGU Advances. Their work is extremely important because tectonic activity most likely translated into creating the conditions for the survival of life on our planet. This was made possible, inter alia, by changing the composition of the oceans and the atmosphere. By understanding the circumstances under which this happened, researchers will be able to determine the exact course of events from billions of years ago, and more effectively search for planets suitable for sustaining life.
The research was led by Nadja Drabon from Harvard University, who, together with her colleagues, analyzed zircons from the so-called green belt. The aim was to reconstruct the circumstances under which these bodies were formed. In the course of the search, it turned out that about 3.8 billion years ago these zirconias contained signatures of hafnium and trace elements that resembled modern rocks formed in subduction zones, i.e. at the edges of tectonic plates.
Reconstructing the geological history of our planet is difficult because the earth's crust is constantly changing, so it is difficult to determine what happened and when. A breakthrough in this case may be a find involving 33 microscopic zircon crystals, dating from 4.15 to 3.3 billion years. They were discovered in the Barberton green belt in South Africa. Due to the wealth of information such crystals can provide, scientists refer to them as time capsules.
Global changes or just local anomalies?
Knowing that the Barberton zircon crystals had formed at the edges of the tectonic plates, Drabon and the rest of her team could confidently conclude that plate tectonics occurred at least 3.8 billion years ago. Geochemical signatures then became surprisingly similar to modern ones, which in turn suggests that the environment began to become more and more friendly to life.
To find out whether the changes at that time were local or global in nature, the scientists compared their findings with data on zircon crystals from the same period from other parts of the world. All indications are that processes such as those observed in the Barberton green belt occurred on a much larger scale. In other words, the Earth began to change, creating conditions conducive to the survival of life.