EPOD 20th - Calcite Crystals and Microbial Activity Within the Earth's Crust

September 18, 2020

Press release Deep biosphere (1)

We’re celebrating 20 years of Earth Science Picture of the Day during the month of September! Today’s photo features a popular EPOD from the past. Thanks to all of our followers (on the blog, Facebook, Instagram and Twitter) for supporting us. Thanks also to all of you who’ve submitted your photos. We’re most appreciative. This EPOD was originally published May 18, 2017.

Photographer: Henrik Drake
Summary Author: Henrik Drake

May 2017 Viewers' ChoiceThe photo above features calcite crystals precipitated in response to microbial activity deep within the Earth's crust -- shown in fractured granitic rock in Sweden. These crystals (about 5 mm in height) act to provide an archive for tracking ancient microbial activity. The tweezers are included for scale.

Methane-munching microbes, an analog for extraterrestrial life, have been living in the deep biosphere for some 400 million years. The knowledge about ancient life in the environment deep under our feet is extremely scarce. In numerous cracks down to depths of 1700 m (5,577 ft) that have been partly sealed by crystals growing within them, an international team of researchers led by Dr. Henrik Drake from Linnaeus University, Sweden, have traced fundamental, ancient microbial processes, including the production and consumption of the greenhouse gas, methane. This is thus far the most extensive study on ancient microbial activity in the continental crust, and findings suggest that microbial methane formation and consumption are widespread in the bedrock here.

This new knowledge of a deep source and sink for methane calls for a re-evaluation of the carbon cycling within the vast continental crust and may even be significant in a long-term global warming perspective. Dr. Christine Heim of the University of Göttingen, Germany, a co-author of the study, states that it's intriguing to find biomarkers of ancient organic remains having surface origins (land plants) preserved within calcite at such great depth. The nutrient source for the microbes at least partly seems to have been coming from the surface. This connection to the surface biosphere may explain why the marks of microbial activity abruptly disappear at around 700 to 800 m in depth. So in essence, cracks in the Earth's crust and on other planets, believed to be omnipresent, may be the perfect graveyards for past biologic activities.

Photo Details: Camera: SONY DSC-RX10; Lens: 24-200mm F2.8; Focal Length: 8.8mm (35mm equivalent: 24mm); Aperture: ƒ/2.8; Exposure Time: 0.017 s (1/60); ISO equiv: 125; Software: Adobe Photoshop Lightroom 6.8 (Windows).