FTIR (Fourier Transform Infrared Spectroscopy) is a non-destructive method that shines infrared light through a sample to measure how its chemical bonds absorb different frequencies. Each molecule vibrates in characteristic ways, producing absorbance peaks at specific wavelengths. Because each resin-producing plant family has its own chemical structure, these peaks form a kind of spectral fingerprint. By comparing fossil amber spectra with modern reference resins, scientists can identify the likely botanical source of the resin, often down to the family level.

 

The recent discovery of amber from the Hollín Formation in Ecuador has expanded our understanding of South America’s Cretaceous forests. Reported in Communications Earth & Environment (Nature Publishing Group), this finding is remarkable not just because it preserves insects, pollen, and plant matter from 112 million years ago, but also because it offers a chemical window into the trees that produced the resin. Central to the analysis is Fourier Transform Infrared Spectroscopy (FTIR), a method widely used to characterize fossil resins.

 

This article explores how FTIR is applied to amber, what it reveals about resin-producing trees, the discovery of two distinct resin types in Ecuador, and why microscopic and geological context are essential to interpret these results.

 

FTIR and Amber: How It Works

 

FTIR (Fourier Transform Infrared Spectroscopy) is a non-destructive method that measures how a material absorbs infrared light. Each molecule vibrates in characteristic ways, and these vibrations create absorbance peaks at specific wavelengths. In the case of resins and ambers:

 

Conifer resins (gymnosperms, e.g., Araucariaceae, Cupressaceae, Pinaceae) show diagnostic absorption bands linked to C–O stretching (~1150–1175 cm⁻¹), CH₂ bending, and certain aromatic ring vibrations.

 

Angiosperm resins differ by containing more esters and carboxyl groups, giving them distinct spectra.

 

When applied to fossil amber, FTIR provides a chemical fingerprint that can be compared to modern reference resins. In Ecuador’s case, the spectra aligned most closely with modern Araucariaceae, pointing to coniferous trees as the dominant resin source.

 

Two Types of Amber Resins in Ecuadorian Research.

 

One of the most intriguing aspects of the Ecuadorian deposit is that it preserves two distinct modes of resin formation:

Aerial amber – Produced above ground, often exuding from trunks and branches. This resin is typically rich in biological inclusions such as insects, spider webs, and plant fragments. In Ecuador, aerial amber preserved at least six arthropod orders, including flies, beetles, wasps, and even a spider web fragment.

 

Subterranean or root amber – Resin exuded below ground, often from roots. Because it is produced in soil rather than exposed to the open environment, this amber rarely contains inclusions. Instead, it provides a chemical and textural complement to aerial amber.

 

The recognition of these two amber types demonstrates that fossil resin is not a single material but a suite of products formed under different ecological conditions. Together, they broaden our view of how resin circulated within ancient forests.

 

Reliability and Limits of FTIR

 

While FTIR is a trusted method in amber studies, its application has important boundaries:

 

Broad family-level resolution – FTIR is powerful for distinguishing resins from different plant families but rarely identifies genus or species.

 

Aromatic vibrations are not definitive – Aromatic bands can overlap across plant families, and millions of years of polymerization may blur subtle distinctions.

 

Dilution and alteration – Inclusions or later chemical overprints (e.g., petroleum hydrocarbons in surrounding rocks) can mask original resin signals.

 

Thus, while FTIR reliably confirms that the Ecuadorian amber came from conifers, it cannot alone rule out contributions from other trees.

 

Why Microscopy Matters

 

To address these limitations, researchers combined FTIR with microscopic and palynological evidence:

 

Pollen and spores – Sediments from the Hollín Formation contained abundant conifer pollen, particularly from Araucariaceae, along with spores and early angiosperm pollen.

 

Wood fibers – Fibrous plant tissue fragments in the amber and surrounding rock supported the coniferous origin.

 

Inclusion diversity – Arthropods and spider webs embedded in aerial amber point to the ecological richness of these forests.

 

This integration strengthens the botanical interpretation, showing that the resin-producing trees were most likely Araucariaceae conifers living alongside ferns and emerging angiosperms.

 

Geological and Ecological Context

 

The amber formed around 112 million years ago (Albian, Early Cretaceous), a time when South America was part of Gondwana. The forests of the Oriente Basin in Ecuador were humid, fluvial–lacustrine systems, where conifers produced abundant resin that could fossilize.

 

However, the amber record is biased. Resin fossilizes only under special conditions, and not all trees produce resin in large quantities. Thus, even though palynological data show early angiosperms and ferns present in the ecosystem, their contribution to the amber record is minimal. The amber captures a conifer-centric picture of the forest, not its full botanical diversity.

This selective preservation reminds us that amber is both a window and a filter: it preserves exquisite details but never the whole forest

 

Comparing Ancient and Modern Resins

By comparing fossil FTIR spectra to modern resins, researchers build bridges across millions of years. In Ecuador’s case, modern Araucariaceae resins offered the closest match, reinforcing the conifer interpretation. This comparative method also ensures that conclusions are grounded in experimental reality rather than abstract inference.

It also highlights a subtle point: the chemical fingerprints of ancient resins may not perfectly match any living resin. Trees evolve, chemistry shifts, and fossilization alters signals. Thus, FTIR is best used as a comparative guide, supported by paleobotanical evidence.

Broader Implications

The Ecuadorian amber contributes to a larger story known as the “Cretaceous Resinous Interval” (125–72 million years ago), when resin production increased globally. This was also a time of evolutionary experimentation, with angiosperms spreading and gymnosperms retreating to new ecological niches.

The Ecuador discovery fills a major gap in South America’s fossil record, showing that Gondwanan forests participated in these global trends. It demonstrates that:

  • Resin production was significant in equatorial Gondwanan forests.

  • Conifers were dominant resin-producers even as angiosperms were emerging.

  • Amber, though selective, preserves both ecological structure (arthropod diversity) and chemical identity (resin source).

Conclusion

FTIR has proven itself an essential tool for amber studies. In Ecuador, it confirmed the Araucariaceae origin of the resin, especially when paired with pollen, spores, and microscopic evidence. The recognition of both aerial and subterranean amber types reveals the multiple pathways by which resin entered the fossil record.

Yet, FTIR is not a magic bullet. Its reliability is strongest at the family level, not species, and its results must be interpreted in a geological and ecological framework. When combined with microscopy, palynology, and modern reference comparisons, FTIR unlocks the chemical and biological secrets of amber without damaging these rare fossils.

The amber of Ecuador is more than fossilized resin: it is a geochemical archive of forests long vanished. By reading its spectra carefully, we gain not only knowledge of Araucariaceae resin but also a richer understanding of Gondwanan ecosystems at a turning point in Earth’s history.