The scientists analyzed zircons from the Barberton Greenstone Belt in South Africa, which is one of the oldest geological regions on Earth. They found that the zircons contained high levels of uranium and thorium, which are radioactive elements that produce heat when they decay. This heat would have been enough to raise the Earth's surface temperature significantly.
The scientists believe that the high temperatures were caused by a combination of factors, including the sun being hotter in the past, the Earth's atmosphere being thinner, and the Earth's crust being more radioactive. They also suggest that the high temperatures may have been responsible for the formation of the Earth's first continents.
The findings of this study have important implications for our understanding of the early Earth. They suggest that the Earth's climate was much more dynamic and variable than previously thought, and that the high temperatures may have played a key role in the development of life on Earth.
Study abstract:
Zircon is the most abundant U-Th-Pb-bearing mineral in the continental crust and thus has great potential to serve as an archive of past crustal temperatures. Most crustal temperature estimates based on zircon trace element data assume that the trace elements entered the zircon crystal lattice during mineral growth. However, recent experimental studies have shown that radiation damage can also enhance trace element diffusion in zircon, potentially leading to overestimated crustal temperatures for old zircon.
Here, we use a diffusion-advection-reaction model to calculate the effect of radiation damage on the trace element profiles of zircon. Our model results show that radiation damage could significantly affect the trace element profiles of zircon that are older than ∼2 Ga. We compare our model-derived trace element profiles to measured profiles from Paleoproterozoic to Neoarchean zircons from the Barberton Greenstone Belt (BGB), South Africa.
Our forward modeling results suggest that metamorphic temperatures for most of the studied zircon grains are within 50°C of temperatures estimated from conventional methods which assumed that trace elements entered the zircons during mineral growth. However, for some old (>3.2 Ga) zircons, our results suggest metamorphic temperatures that are up to 150°C lower.
Zircon ages suggest that the BGB was metamorphosed at around 3.2–3.5 Ga. Our results suggest that the BGB experienced a rapid increase in temperature from ∼500 to ∼850°C at ∼3.5 Ga, followed by a slow cooling to ∼750°C by 3.2 Ga. These results provide valuable information about the thermal evolution of the BGB and provide new insights into the early evolution of the Earth.
