First Living Organisms Help
Introduction to the First Living Organisms
We will probably never know for sure exactly how life began – Why? The first living things (such as primitive bacteria) left behind no fossil record . Soft-bodied micro-organisms, such as the ancient bacteria, had no hard parts. Hence, their remains were rarely preserved.
Fossil means “to dig.” Thus, the fossil record consists of the remains of ancient living things that have been preserved and “dug” up. With no hard body parts preserved, then, the first living creatures essentially left no fossils to be “dug” up later!
Nevertheless, many ancient soft-bodied bacteria created stromatolites (stroh- MAT -uh- lights ) – “layered rocks.” Even today, huge mounds of bacterial colonies live in shallow ocean water. Fine particles of dirt, calcium, and other minerals in the seawater, collect as sediment upon the colonies. This sediment eventually arranges into thin “layers” ( stromas ) streaking through each bacterial mound. As the layers or stromas become calcified (hardened with calcium sediment), they turn into layered rocks.
Figure 3.2 shows such a stromatolite. Among the oldest-known fossils are narrow, filament (“thread”)-shaped bacteria, preserved within ancient stromatolite rock from Western Australia. They are about 3.5 billion years old.
The First Living Organisms: Tiny Green Threads Without Any “kernels”
In the living stromatolites found on present-day Earth, the bacteria are usually bluish-green in color. This green color indicates that they engage in photosynthesis ( FOH -toe- sin -theh-sis). Photosynthesis is the use of “light” ( photo ) to “place (things) together” ( synthesis ). Specifically, photosynthesis is the process whereby certain types of organisms (usually green) use the energy in sunlight to make sugar molecules for themselves. Thus, the first ancient bacteria probably looked like tiny bluish-green threads or filaments. Further, each of these ancient, threadlike, green bacteria cells lacked a nucleus.
In Greek, the word part for “nucleus” or “kernel” is kary ( KAIR -ee). Consequently, these ancient threadlike bacteria are often called prokaryotes ( proh-KAIR -ee-oats). The reason for this name is that, being extremely ancient, the prokaryotes probably appeared “before” ( pro -) other types of more advanced cells having a “nucleus” ( kary ).
Cells With Nuclei: In Come The “kernels”
For well over a billion-and-a-half years, it appears that the prokaryotes (photosynthetic cells without nuclei) were alone on this planet. All that time, however, these tiny green cells produced abundant amounts of oxygen (O 2 ) molecules, since oxygen is one of the main by-products of photosynthesis. The prokaryotes accomplished the critical task of making Earth’s atmosphere capable of sustaining aerobic (air- OH -bik) metabolism. This is the type of metabolism that “pertains to” (- ic ) “oxygen-or-air-using” ( aer ) “life” ( ob ).
The stage was thus set for the appearance of more complex cells, many of which had aerobic metabolisms dependent upon a ready supply of oxygen. About 2.1 billion years ago, numerous eukaryotes ( yew-KAIR -ee-oats) evolved from the prokaryotes. Each eukaryote cell has a “good” (eu-) “nucleus” (kary) surrounded by its own membrane. In addition, the eukaryote cell contains numerous other organelles, each enclosed within its own individual membrane. Besides the nucleus, another very important membrane-covered organelle is the mitochondrion ( my -toe- KAHN -dree-un). The mitochondrion carries out most of the aerobic (oxygen-using) metabolism within the eukaryote cell.
Figure 3.3 provides a summary of the above information. It shows that there are two basic types of cells – prokaryotes (cells without a nucleus) and eukaryotes (cells having a nucleus and other organelles surrounded by membranes). Further, we see that the major examples of prokaryotes now in existence are the bacteria. The cells of nearly all other organisms besides bacteria, in contrast, are eukaryotes. (A detailed discussion of cell anatomy and physiology will be provided in Chapter 5.)