Outside the Sexi village in Peru, a fossilized forest holds the secrets to South America's primeval past. When researchers first came upon the petrified trees in the hills in the outskirts of the village roughly 20 years ago, few details were known about their age and what preserved the trees.

Researchers began by dating rock samples and understanding volcanic processes that could have preserved the fossils. Then the research team pieced together the mysterious story of Peru's petrified forest.

They discovered that roughly 39-million-years-ago a volcanic eruption in Northern Peru engulfed the forests in ash that led to its preservation, the Conversation reported.

Peru's Petrified Forest

On the day of the volcanic eruption, ash poured from the sky, stripping leaves off the trees. Flows of ash materials then moved through, breaking trees and carrying the logs into the river basin where they inevitably became buried and preserved.

Millions of years later, the Andes rose, carrying with it the fossils that were then exposed to the forces of erosion.

The petrified forest, locally known as El Bosque Perificado Piedra Chamana, became the first fossilized forest in the South American tropics. Today, the forests aid paleontologists to better understand the history of the megadiverse forests of the New World and the past climatic and environmental factors that thrived in South America during its primeval past.

Researchers examined thin slices of petrified wood using microscopes and mapped out the mix of flora that thrived in the area before man walked the Earth.

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Petrified Forest Under the Lens

For researchers to identify which trees had grown in the forest before the catastrophic volcanic eruptions, thin samples of petrified materials would need to be studied under the scrutiny of a microscope. It was no simple task due to the volume and diversity of specimens available at the site.

Researchers tried to sample the diversity of wood materials by relying on the flora's observable features or using small hand-held microscopes. Small blocks were cut from the specimen that gave scientists insight into the tree's anatomy. This showed researchers in detail the many features of the trees, including wood fibers, vessels, and living-tissue components.

Clues to South America's Primeval History

Researchers discovered that many of the fossilized trees have present-day close relatives in the lowland tropics of South America.

Some of the samples had defining features of lianas trees, while others would have been large canopy trees. An Avicennia mangrove was discovered, giving clues on the South American tropics during its primeval history. The mangrove discovery suggests that the forest first grew in low elevations near the coast before the Andes began to rise.

Petrified leaves that hand smoothened edges, compared to the toothed edges common in cooler climates, indicated that the forests thrived in warm conditions.  Based on previous studies, researchers knew that as the forest grew in the past million years, the planet was considerably warmer than today. 

Although many similarities were reported between fossilized trees in the petrified forest and trees today, one tree featured anatomical characteristics that are unusual for South American tropics: the Dipterocarpaceae species only had one other representative in South America but is commonplace in South Asian rainforests.

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