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Secrets of the Ancient Earth: Why is the carbon isotope deviation so surprising between 230 and 210 million years ago?
The changes in carbon isotopes throughout the Earth's history are an important indicator for studying the global carbon cycle. In particular, the Lomagundi-Jatuli carbon isotope event (LJE) that occurred between 230 and 210 million years ago showed an astonishing carbon isotope deviation, revealing many mysteries of the ancient Earth. During this period, δ13C values in marine carbonate rocks ranged from +5 to +30‰, which is very different from the carbon isotope trends we have observed so far.
During this period, the amount of buried organic carbon may have increased two to three times, and the entire process spanned millions of years.
Scientists analyze the δ13C values in ocean carbonate rocks to gain insight into the evolution of the global carbon cycle. The flow of carbon not only involves the interaction between the atmosphere, ocean and land, but also reflects the importance of processes such as photosynthesis, respiration and mineral dissolution in this event. As we gain a better understanding of carbon mobility, we are becoming more aware of its impact on the concentration of carbon dioxide in the Earth's atmosphere, which in turn affects the Earth's climate.
Initial studies suggested that the high δ13C values of the LJE were due only to local increases in organic carbon at certain locations, but many marine carbonate rocks around the world have shown similar increases over time. This changes the nature of the event to a global increase.
Region and time range
According to the study, the duration of this event was approximately between 249±9 million years and 128±9.4 million years, involving all continents in the world except Antarctica. During this period, the changes in δ13C values found in the Ranemosa Group and Funai area have made the scope of LJE no longer limited to a specific region. During this period, the profile can be tens of meters thick, providing us with a glimpse into the grandeur of the carbon cycle at the time.
Research Methods
In geology, choosing the right method for dating stratigraphic layers is crucial. For the age dating of marine carbonate rocks, commonly used techniques include thermal ionization mass spectrometry (TIMS) and isotope dilution-thermal ionization mass spectrometry (ID-TIMS). These techniques are crucial for assessing the accuracy of carbon data and can control the measurement error of δ13C values to within 1‰.
These methods can effectively separate and measure different isotopes by vaporizing samples at high temperatures, further revealing the ratio of lead to uranium in the rock and thus determining the age of the rock.
Causes of LJE
The scientific community has proposed a variety of hypotheses about the causes of LJE. One of the theories is that the LJE is related to the Great Oxygenation Event (GOE), in which the carbon storage of alternative processes changed the balance of the carbon cycle, thereby releasing more oxygen. In addition, the process of oxidizing iron carbonate has also been proposed to explain this phenomenon, because the amount of carbon dioxide released by this process far exceeds the amount of oxygen consumed, further promoting the burial of organic matter.
Another hypothesis proposes that major tectonic changes may have led to increased release of volcanic carbon dioxide, which also contributed to the deposition of carbonates and organic matter.
Impacts of climate change
As LJE conducts in-depth research, we gradually realize that this event not only affected the early carbon cycle of the Earth, but also laid the foundation for subsequent climate change. How this high-carbon isotope event may affect the climate change issues we are currently facing in the future is worthy of our in-depth exploration and thinking.
As we gain a deeper understanding of LJE, can we uncover more secrets of the ancient Earth and gain some warnings and inspiration for today’s climate change?
