When Were the First Continents in the Universe Formed?
Continents are an essential component for supporting life on Earth. They ‘float’ on the Earth’s mantle and are kept from solidifying by heat from the planet’s core. The question is, when did the first continents form in the Universe? Jane Greaves, an astronomy professor at Cardiff University, set out to find the answer. Her research aims to improve the search for habitable planets by identifying locations with continents and plate tectonics.
Plate tectonics play a crucial role in moderating Earth’s temperature, allowing heat to vent from the core and maintaining Earth’s protective magnetosphere. While plate tectonics may not have been active when life first appeared on Earth billions of years ago, they are likely necessary for more complex life forms like humans to evolve. Therefore, the search for habitable planets should prioritize rocky planets with plate tectonics and continents.
Greaves devised a method to trace which planets might have continents by examining their potential for plate tectonics. The production of enough heat in a planet’s core indicates active plate tectonics. This heat is generated by the decay of radioactive isotopes found in the core. These elements, such as Uranium and Thorium, are formed in neutron stars and supernova explosions. By analyzing stellar abundances of chemical elements and combining them with the ages of the stars, Greaves determined when continents may have formed on different types of stars.
Her results show that continents appeared on Earth about 3 billion years ago, approximately 9.5 billion years after the beginning of the Universe. Thin-disk stars, which are younger and have higher metallicity, formed rocky planets with continents about 2 billion years before Earth’s continents. Thick-disk stars, which are older and metal-poor, produced continents even earlier, around 4 to 5 billion years before Earth’s.
Greaves also found a correlation between continents and the iron content in stars. Planets formed continents earlier on stars with lower metallicity compared to our Sun. These stars with sub-solar metallicity may be promising targets for the search for habitable exoplanets with continents.
The upcoming Habitable Worlds Observatory aims to find rocky exoplanets with continents, and Greaves’ research provides valuable insights into potential target stars. Out of the 46 FGK stars on its top-tier target list, 15 of them align with her results. If these findings are accurate, there could be systems with more advanced biospheres than Earth within this sample alone.
The next step is to investigate the abundance of radioactive isotopes like thorium and potassium, which produce radiogenic heat. This could uncover older systems where life on land may predate life on Earth. These elements, along with iron, are critical to a planet’s core size, gravity, and internal temperature, which in turn affect the conditions for plate tectonics, continents, and the viability of life.
While previous research suggests a higher likelihood of Earth-like planets with continents in earlier galactic history, there is still much to learn about exoplanets and their habitability. The search for life and understanding the geophysical conditions necessary for its existence require patience and the continued advancement of telescopes.
In conclusion, the formation of continents in the Universe predates Earth by billions of years. Greaves’ research sheds light on potential targets for finding habitable exoplanets with continents and hints at the possibility of more advanced biospheres than our own. Further investigations into radiogenic heating and stellar abundances will contribute to our understanding of the evolution of planets and the conditions required for life.
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