|
 |
This is a 2-methylhopane, a biomarker unique to cyanobacteria (Summons et al. Nature 400:556, 1999). These geohopanes are abundant in sediments dating back to 2.7 Ga (Brocks et al. Science 285:1033, 1999). The detection of 2- methylhopanes in these ancient sediments sets a minimum age for the evolution of cyanobacteria. It was within this group of bacteria that the process of oxygenic photosynthesis first evolved, and so detection of these molecular fossils tell us that biogenic oxygen was present very early in Earth' history. Oxygen would have been toxic to the anaerobic bacteria that lived in these early microbial mats. Bacteria would have to learn first to tolerate and then to use oxygen for aerobic respiration and oxygen-requiring biosynthesis of more complex biomolecules. Early Earth's bioshere was somewhat reducing and so it would take more than a billion years for sufficient oxygen to be produced to escape into atmosphere. |
||||||
|
Last Modified December 8, 1999
Created & maintained by: Maria Farmer Responsible NASA Official: Linda Jahnke ljahnke@mail.arc.nasa.gov |
|||||||
