Earliest life and the carbon cycle

After it was formed 4.6 billion years ago, the Earth was subjected to a heavy bombardment by meteorites, which decreased after about 700 million years. This allowed the Earth’s crust to stabilise, and just 100 million years later life in the form of plankton had colonised the oceans. Traces of these planktonic organisms are found today as biogenic carbon in the world’s oldest rocks at Isua in the Godthåb Fjord region. The exciting aspect of these early organisms is that they might have contributed to reducing the quantity of the greenhouse gas CO₂in the atmosphere in an early phase of the Earth’s geological development, thus helping reduce the Earth’s temperature at a time when radiation from the Sun underwent a pronounced increase. It has not yet been determined whether this is the case, but one or more factors must have prevented total evaporation of the early seas and consequent desiccation of the planet. The project will focus on the 3.8-billion-year-old marine metasediments from Isua; geochemical and geological studies will focus on the incipient interplay between the Earth and its living organisms. An international research team will look for signs of microbial decomposition of the seafloor some 3.8 billion years ago. The project will similarly try to determine the origin of water on Earth, and how the water cycle functioned in the early history of the Earth.

In order to establish a modern analogy to these early sediments found at Isua, Holocene carbon cycles in the West Greenland fjord systems will be studied. At a depth of several metres below the seabed, large quantities of methane gas are produced as a result of the decomposition of organic matter. Methane, like carbon dioxide, is both an important component of the carbon cycle and an important greenhouse gas. There is concern about increased methane release from Arctic areas, since this may be linked to, and result in, increased rates of global warming. In this context, the decomposition of organic material and methane release from the seabed will be examined in the most recent parts of the sediment cores in order to increase our understanding of the carbon cycle in the Arctic marine environment, including the link to present as well as past climate change.