Fossil leaves reveal high levels of atmospheric carbon 23 million years ago

Hyperaxion Aug 22, 2020

The findings shed light on the possible consequences of the increase in carbon dioxide in the atmosphere today.

After analyzing leaves from a 23 million-year-old forest, scientists at the University of Otago in New Zealand and the University of Connecticut in the United States found an association between high levels of atmospheric carbon dioxide (CO2) and increased plant growth on the planet, what they called “global greening”.

The results were published this week in the journal Climate of the Past.

Fossil leaves reveal high levels of atmospheric carbon 23 million years ago
(Credit: Jennifer Bannister / University of Otago).

The discovery sheds light on how the increase in CO2 in the atmosphere affects plant growth and the consequences this will bring in the coming decades, when carbon dioxide levels will be close to those of millions of years ago.

The researchers collected leaves from a region of New Zealand that contains fossils of plants, algae, spiders, beetles, flies, fungi, and other living things from the early Miocene – between 23 and 5.3 million years ago.

Before this study was published, it was already widely accepted in the scientific community that CO2 was high at that time, and that some plants could collect it more efficiently to perform photosynthesis.

The researchers analyzed carbon isotopes in the leaves of six species of trees found in the region and were able to identify the concentration of atmospheric carbon at that time.

They found that atmospheric CO2 levels were not 300 parts per million (ppm), as previous studies suggested, but 450 ppm.

Scientists also noted that the trees were super-efficient at sucking carbon without losing much water. This allowed them to grow in very dry areas.

“The amazing thing is that these leaves are basically mummified, so we have their original chemical compositions, and can see all their fine features under a microscope,” said Tammo Reichgelt, a professor of geosciences at the University of Connecticut and lead author of the study.

Previous studies have shown that when CO2 levels rise, many plants increase their rate of photosynthesis, because they can remove carbon from the air more efficiently and conserve water by doing so.

A Foulden fossil leaf magnified 400x.
A Foulden fossil leaf magnified 400x. (Credit: Tammo Reichgelt/University of Connecticut).

In fact, a 2016 study based on satellite data shows an effect of “global greening”: almost half of the planet’s vegetated lands have seen an increase in leaf volume since 1980.

This trend is expected to continue with the increase in CO2 levels, mainly as a result of human activity.

Also, not all plants can take advantage of the increase in CO2 in the atmosphere, and among those that do, the results may vary depending on the temperature and availability of water or nutrients.

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