The Hadean crust of Hudson Bay
Along the eastern shore of Hudson Bay in northern Quebec lies a sequence of metamorphosed volcanic and sedimentary rocks known as the Nuvvuagittuq Supracrustal Belt (NSB). This remote outcrop contains some of the oldest known rocks on the planet. The age is a subject of scientific debate, but estimates place the formation of these rocks between 3.75 and a staggering 4.28 billion years ago. This geological time frame, the Hadean Eon, means the NSB records Earth's earliest conditions, just a few hundred million years after the planet itself formed.
The rocks were once part of a deep-sea hydrothermal vent system on the ocean floor. Through tectonic activity over billions of years, this section of ancient oceanic crust was lifted and merged with the continental landmass, preserving its unique chemical and physical history. The primary rocks in the belt are metamorphosed mafic volcanic rocks and chemical sedimentary rocks, including banded iron formations. These formations are important to geochemists and astrobiologists searching for the earliest signs of life.
Microbes made of rust
In 2017, researchers examining jasper rock samples from the NSB announced the discovery of microscopic filaments and tubes made of hematite, a form of iron oxide. These structures are morphologically similar to the remains of modern iron-metabolizing bacteria found near today's deep-sea vents. The filaments are tiny, about half the width of a human hair, and up to half a millimeter long. More recent analysis showed even larger and more complex structures, including a centimeter-long stem with parallel branches.
The scientific team, led by Dominic Papineau and Matthew Dodd, presented evidence for a biological origin. The rocks containing the structures also hold minerals like graphite, apatite, and carbonate, which indicate biological matter. The specific isotopic signature of carbon in the samples is consistent with biological processes. If these structures are confirmed as microfossils, they predate the next oldest contenders, found in Western Australia, by at least 300 million years.
The claim is not without controversy. Some scientists suggest that similar tube-like shapes can be formed through non-biological chemical reactions, known as "chemical gardens," in certain hydrothermal settings. Others question the age of the rocks themselves. The debate continues, but if the structures are biological, they show that a variety of microbial life may have existed on a primordial Earth very soon after its formation.