biology question

Question

Mounds of bacteria once covered young Earth. true or false?

Answer 1

True. Bacteria are ubiquitous, meaning they were everywhere. There are fossil records that indicate that there were mounds of bacteria on young earth.

Answer 2

Dear Justin,

The answer is true in a superficial way but technically false or unknown, so I will elaborate.

During the Archaean Eon (4.0 to 2.5 billion years ago), mats of bacteria trapped and bound fine-grained sediments, then grew through them, and repeated to form mound structures called stromatolites.

Here is where the technicalities come in:

1. Stromatolites are not mounds of pure bacteria. They are almost purely made of layered sediments. Microscopic analyses of fossil stromatolites show that their insides are mostly rock-solid, and fossils of bacteria are absent from them. However, paleontologists infer that they were formed from prehistoric bacteria based on observations of how modern stromatolites (with living bacteria) form. These can be found in the Bahama Banks and Shark Bay, Australia, as seen in the photo from a University of California Museum of Paleontology webpage on the Archean: https://ucmp.berkeley.edu/precambrian/archean_hadean.php
2. Stromatolites are only found in shallow-water environments. It is unknown how prevalent these environments were during the time of Archean stromatolitic bacteria as to say that these stromatolites "covered" young Earth. Reconstructing Archean environments is very challenging given how rare rocks from this time are, as seen in Figure 1 of this publication: https://doi.org/10.1144/SP449.10

I hope that helps and intrigues you!

-Nicholas

Works Cited

Knoll, Andrew Herbert. "The fossil record of microbial life." in Fundamentals of Geobiology. (2012). https://doi.org/10.1002/9781118280874.ch16