<< Chapter < Page Chapter >> Page >

The first microbial mats likely obtained their energy from chemicals found near hydrothermal vents. A hydrothermal vent is a breakage or fissure in the Earth’s surface that releases geothermally heated water. With the evolution of photosynthesis about 3 billion years ago, some prokaryotes in microbial mats came to use a more widely available energy source—sunlight—whereas others were still dependent on chemicals from hydrothermal vents for energy and food.

The part a photo shows a reddish-yellow mound with small chimneys growing out of it. Part b micrograph shows rod-shaped bacteria about two microns long swimming over a thicker mat of bacteria.
This (a) microbial mat, about one meter in diameter, grows over a hydrothermal vent in the Pacific Ocean in a region known as the “Pacific Ring of Fire.” The mat helps retain microbial nutrients. Chimneys such as the one indicated by the arrow allow gases to escape. (b) In this micrograph, bacteria are visualized using fluorescence microscopy. (credit a: modification of work by Dr. Bob Embley, NOAA PMEL, Chief Scientist; credit b: modification of work by Ricardo Murga, Rodney Donlan, CDC; scale-bar data from Matt Russell)

Stromatolites

Fossilized microbial mats represent the earliest record of life on Earth. A stromatolite is a sedimentary structure formed when minerals precipitate out of water by prokaryotes in a microbial mat ( [link] ). Stromatolites form layered rocks made of carbonate or silicate. Although most stromatolites are artifacts from the past, there are places on Earth where stromatolites are still forming. For example, growing stromatolites have been found in the Anza-Borrego Desert State Park in San Diego County, California.

 Photo A shows a mass of gray mounds in shallow water. Photo B shows a swirl patter in white and gray marbled rock.
(a) These living stromatolites are located in Shark Bay, Australia. (b) These fossilized stromatolites, found in Glacier National Park, Montana, are nearly 1.5 billion years old. (credit a: Robert Young; credit b: P. Carrara, NPS)

The ancient atmosphere

Evidence indicates that during the first two billion years of Earth’s existence, the atmosphere was anoxic , meaning that there was no molecular oxygen. Therefore, only those organisms that can grow without oxygen— anaerobic    organisms—were able to live. Autotrophic organisms that convert solar energy into chemical energy are called phototrophs , and they appeared within one billion years of the formation of Earth. Then, cyanobacteria , also known as blue-green algae, evolved from these simple phototrophs one billion years later. Cyanobacteria ( [link] ) began the oxygenation of the atmosphere. Increased atmospheric oxygen allowed the development of more efficient O 2 -utilizing catabolic pathways. It also opened up the land to increased colonization, because some O 2 is converted into O 3 (ozone) and ozone effectively absorbs the ultraviolet light that would otherwise cause lethal mutations in DNA. Ultimately, the increase in O 2 concentrations allowed the evolution of other life forms.

This photo shows a woman squatting next to a stream of green-colored water.
This hot spring in Yellowstone National Park flows toward the foreground. Cyanobacteria in the spring are green, and as water flows down the gradient, the intensity of the color increases as cell density increases. The water is cooler at the edges of the stream than in the center, causing the edges to appear greener. (credit: Graciela Brelles-Mariño)

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ucd bis2a intro to biology v1.2' conversation and receive update notifications?

Ask