A volcanic eruption 39 million years ago buried a forest in Peru – now the petrified trees are revealing South America’s primeval history

With the proof uncovered by paleontologists, an artist sketched El Bosque Petrificado Piedra Chamana because it might need appeared lengthy earlier than people. Mariah Slovacek/NPS-GIP

In the hills exterior the small village of Sexi, Peru, a fossil forest holds secrets and techniques about South America’s previous thousands and thousands of years ago.

When we first visited these petrified trees greater than 20 years ago, not a lot was identified about their age or how they got here to be preserved. We began by dating the rocks and learning the volcanic processes that preserved the fossils. From there, we started to piece collectively the story of the forest, ranging from the day 39 million years ago when a volcano erupted in northern Peru.

Ash rained down on the forest that day, stripping leaves from the trees. Then flows of ashy materials moved by way of, breaking off the trees and carrying them like logs in a river to the space the place they had been buried and preserved. Millions of years later, after the modern-day Andes rose and carried the fossils with them, the rocks had been uncovered to the forces of abrasion, and the fossil woods and leaves once more noticed the gentle of day.

This petrified forest, El Bosque Perificado Piedra Chamana, is the first fossil forest from the South American tropics to be studied in element. It helps paleontologists like us to grasp the history of the megadiverse forests of the New World tropics and the previous climates and environments of South America.

By analyzing skinny slices of petrified wooden underneath microscopes, we had been in a position to map out the mixture of trees that thrived right here lengthy earlier than people existed.

An artist's illustrations of each of the most common variety of trees found, plus cross-sections of the fossil wood as seen under a microscope

An artist’s illustrations of every of the commonest number of trees discovered, plus cross-sections of the fossil wooden as seen underneath a microscope

Petrified wooden underneath a microscope

To determine the varieties of trees that had been rising in the forest earlier than the eruption, we wanted skinny samples of the petrified wooden that may very well be studied underneath a microscope. That was not really easy due to the quantity and variety of fossil wooden at the website.

We tried to pattern the range of the woods by counting on options that may very well be noticed with the bare eye or with small hand-held microscopes, issues like the association and width of the vessels that carry water upwards inside the tree or the presence of tree rings. Then we lower small blocks from the specimens, and from these we had been in a position to put together petrographic skinny sections in three planes. Each aircraft provides us a totally different view of the tree’s anatomy. They enable us to see many detailed options referring to the vessels, the wooden fibers and the living-tissue element of the wooden.

Three magnified cross-sections from a tree fossil

Three magnified cross-sections from a tree fossil

Based on these options, we had been in a position to seek the advice of previous research and use data in wood databases to seek out out what varieties of trees had been current.

Clues in the woods and leaves

Many of the fossil trees have shut family members in the present-day lowland tropical forests of South America.

One has options typical of lianas, which are woody vines. Others seem to have been massive cover trees, together with family members of recent Ceiba. We additionally discovered trees that are well-known in the forests of South America like Hura, or sandbox tree; Anacardium, a sort of cashew tree; and Ochroma, or balsa. The largest specimen at the Sexi website – a fossil trunk about 2.5 ft (75 cm) in diameter – has options like these of Cynometra, a tree in the legume household.

The discovery of a mangrove, Avicennia, was extra proof that the forest was rising at a low elevation close to the sea earlier than the Andes rose.

The fossil leaves we discovered offered one other clue to the previous. All had clean edges, relatively than the toothed edges or lobes that are extra widespread in the cooler climates of the mid- to excessive latitudes, indicating that the forest skilled fairly heat circumstances. We know the forest was rising at a time in the geologic previous when the Earth was much warmer than as we speak.

Fossilized leaves with clear detail.

Fossilized leaves with clear element.

Although there are many similarities between the petrified forest and present-day Amazonian forests, a few of the fossil trees have anatomical options that are uncommon in the South American tropics. One is a species of Dipterocarpaceae, a group that has only one other representative in South America however that’s widespread as we speak in the rainforests of South Asia.

An artist brings the forest to life

Our idea of what this historic forest was like expanded once we had a chance to collaborate with an artist at Florissant Fossil Beds National Monument in Colorado to reconstruct the forest and panorama. Other areas with fossil trees embody Florissant, which has big petrified redwood stumps, and Petrifed Forest National Park in Arizona.

Working with the artist, Mariah Slovacek, who can be a paleontologist, made us assume critically about many issues: What would the forest have appeared like? Were the trees evergreen or deciduous? Which had been tall and which shorter? What would they’ve appeared like in flower or in fruit?

We knew from our investigation that a lot of the fossil trees had been more likely to have been rising in a streamside or flooded-forest location, however what about the vegetation rising again from the watercourses on larger floor? Would the hills have been forested or supported drier-adapted vegetation? Mariah researched as we speak’s family members of the trees we recognized for clues to what they may have appeared like, equivalent to what form and colour their flowers or fruits might need been.

A large petrified log on open ground with rugged hills in the background

A massive petrified go browsing open floor with rugged hills in the background

No fossils of mammals, birds or reptiles from the similar time interval have been discovered at the Sexi website, however the historic forest actually would have supported a range of wildlife. Birds had diversified by that point, and reptiles in the crocodile household had lengthy swum the tropical seas.

Recent paleontological discoveries discovered that two necessary teams of animals – monkeys and caviomorph rodents, which embody guinea pigs – had arrived on the continent at about the time the fossil forest was rising.

With this data, Mariah was in a position to populate the historic forest. The result is a lush, waterside forest of tall flowering trees and woody vines. Birds swoop by way of the air and a crocodile splashes simply offshore. You can nearly think about that you just had been there in the world of 39 million years ago.

This article is republished from The Conversation, a nonprofit information website devoted to sharing concepts from tutorial consultants. It was written by: Deborah Woodcock, Clark University and Herb Meyer, National Park Service.

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Deborah Woodcock has obtained funding from the American Philosophical Society, the National Science Foundation, and National Geographic.

Herb Meyer has been supported in this undertaking as an worker of the National Park Service, with extra funding offered by The Friends of the Florissant Fossil Beds, the National Science Foundation, and National Geographic.

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