Ancient Asteroid Impact in Sweden Reveals Potential for Subsurface Life
A massive impact crater hidden beneath the picturesque landscapes of Sweden is yielding new insights into the potential for ancient life, as scientists continue to unravel the mysteries of the Siljan Ring. This remarkable geological feature, formed approximately 380 million years ago, is not only the largest known impact structure in Europe but also a promising site for astrobiological research.
Impact craters are a ubiquitous feature of every continent on Earth, though many have been erased by erosion or concealed by geological processes. This week, a renewed focus on satellite imagery highlights some of the planet’s most compelling impact sites. The images and information discussed here were originally published on July 21, 2021.
Sweden’s “Miniature” Landscape Hides a Cosmic Secret
Dalarna County, often referred to as “Sweden in miniature” due to its diverse terrain of lakes, forests, and mountains, is a popular destination for those seeking idyllic scenery and cultural experiences. However, beneath this tranquil facade lies evidence of a cataclysmic event from the Late Devonian period.
Around 380 million years ago, a large asteroid collided with the land that now comprises south-central Sweden. The impact was so forceful that it left a lasting impression on the landscape, one that remains visible even after hundreds of millions of years of weathering. The structure is particularly prominent when viewed from space.
The Siljan Ring: A Giant Among Impact Craters
The Siljan impact structure, also known as the “Siljan Ring,” was captured in detail on June 24, 2020, by the Operational Land Imager (OLI) on Landsat 8. Spanning more than 50 kilometers (30 miles) in diameter, Siljan ranks among the top 20 largest impact structures on Earth.
Geological surveys reveal that the center of the crater exhibits a slight uplift, while the surrounding area is characterized by a ring-like graben, or depression. This depression is partially filled with water, forming Lake Siljan, the largest lake within the crater, which connects to Lake Orsa through a small river.
Uncovering a Hidden History
For millennia, local populations lived near the crater without understanding its cosmic origins. It wasn’t until the late 1960s that scientists, utilizing drill cores, began to uncover the complex geological history buried deep beneath the surface.
Ongoing research continues to shed light on the crater’s unique characteristics. A 2019 study indicated that the deeply fractured rocks within the crater could potentially harbor ancient life. This hypothesis was further supported by a 2021 paper detailing the discovery of fossilized remains of fungi at a depth exceeding 500 meters.
The Siljan Ring serves as a compelling reminder of Earth’s dynamic history and the potential for life to exist in unexpected environments. As research progresses, this ancient impact site promises to yield even more profound insights into our planet’s past and the possibilities for life beyond Earth.
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen.
