Final answer:
Microbial mats are multi-layered biofilms primarily consisting of bacteria and archaea, possibly representing Earth's earliest life forms. They often grow on moist surfaces and exhibit a range of colors due to the diverse metabolic pathways of their composite prokaryotes. These mats can form stromatolites, which are layered sedimentary rocks providing a record of early life.
Step-by-step explanation:
Microbial Mats
Microbial mats are essential biological communities where various prokaryotes, primarily bacteria and archaea, form multi-layered sheets. From fossil records, we know that microbial mats may date back about 3.5 billion years ago, suggesting they represent some of the earliest forms of life on Earth. These mats are just a few centimeters thick and typically found on moist surfaces where different materials interface, such as over hydrothermal vents in regions like the "Pacific Ring of Fire."
Structure and Composition
The layers in a microbial mat consist of different prokaryotes that perform various metabolic pathways, contributing to the mat's array of colors. These prokaryotes are bound together by a sticky substance they secrete, known as the extracellular matrix. This matrix helps to retain microbial nutrients within the mat structure.
Energy Sources and Stromatolites
The oldest microbial mats likely sourced energy from chemicals around hydrothermal vents, but some prokaryotes evolved to harness sunlight through photosynthesis about 3 billion years ago. Microbial mats can become fossilized over time, forming structures called stromatolites, which are layered rocks made of carbonate or silicate. Living stromatolites can still be found in some parts of the world, such as the Anza-Borrego Desert State Park in California.