Question

How did prokaryotes early in Earth’s history alter the environments on earth?

Answer 1

Prokaryotes are organisms that lack a distinct nucleus and other organelles due to the absence of internal membranes. Bacteria are the best known prokaryotic organisms. The lack of internal membranes distinguishes them from eukaryotes.

Complete answer:
Prokaryotes are found everywhere. They form the majority of living things in all ecosystems. Some prokaryotes thrive in harsh environments that are inhospitable for most living things. Prokaryotes help in recycling of essential nutrient substances such as carbon and nitrogen and they drive the evolution of new ecosystems. Prokaryotes have existed on Earth since long before multicellular life appeared.
Early Earth’s atmosphere was anoxic, meaning that there was no molecular oxygen and was subjected to strong radiation. Therefore, only those organisms that can grow without oxygen, i.e. anaerobic organisms, were able to live. Thus, the first prokaryotes flourished in ocean depths or beneath the surface of the Earth, where they were more protected.
The first prokaryotes obtain their energy from chemicals found near hydrothermal vents. With the evolution of photosynthesis about 3 billion years ago, some prokaryotes such as cyanobacteria discovered how to extract energy from the sun by photosynthesis. This results in the accumulation of oxygen in the oceans which oxidise iron in the ocean to form iron oxide deposits. After all of the iron in the oceans was oxidized, free oxygen started to accumulate in the atmosphere.
An oxygen atmosphere changed the course of biological evolution in favour of organisms who started to use oxygen for metabolism. Prokaryotes were likely the ancestors of eukaryotic cells, which eventually evolved into multicellular organisms.

Note: Blue-green algae, also called cyanobacteria, are a heterogeneous group of prokaryotic, principally photosynthetic organisms. Cyanobacteria have a great resemblance to eukaryotic algae. But, algae have been reclassified as protists, whereas the prokaryotic nature of the blue-green algae has caused them to be classified with bacteria in the prokaryotic kingdom Monera.