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Section 22_3: History of Life on Earth

Page history last edited by Derek Weber 11 years, 2 months ago

Grading Sheet (Anthony)


A. Summary

• Place the appearance of prokaryotic and eukaryotic organisms within the four eons of geologic time.

• List several environmental influences on the emergence and disappearances of species.

• Trace the evolution of single-celled and multicellular eukaryotes through the different eras and periods in the geological time scale.


According to a number of fossilized rocks, dated up to about 3.5 billion years ago, the first prokaryotes were believed to be formed in the early Archaen era. The first kind of prokaryotes were believed to be cyanobacteria, the photosynthetic precursor to the chloroplasts in modern day plant cells. Since oxygen was not yet introduced into the atmosphere, those prokaryotic cells were believed to have used only anaerobic respiration, namely, respiration without oxygen. They used photosynthesis to convert the atmospheres carbon dioxide to oxygen (the equation is 6 CO2(gas) + 12 H2O(liquid) + photons → C6H12O6(aqueous) + 6 O2(gas) + 6 H2O(liquid) for those who need a reminder). In fossils they would form layered structures known as stromatolites, which would be submerged underwater. These cyanobacteria would not only form large numbers of carbon-based molecules from carbon dioxide and prokaryotes with aerobic respiration, but would eventually lead to the first eukaryotes in history on Earth.

The first multicultural eukaryotics originated about 1.5 billion years ago, in the Proterozoic eon. Some believed the first multicellular organism were the result of a symbiotic union, in which a bacterial and an archael cell fused. Others believed it was the result of an endosymbiotic union in which an archael cell engulfed a bacterial cell. Either way, they are the result of a union between bacterial and archael cells. The nucleus, ER, and golgi were formed by the endomembrane system, and the mitochondria and chloroplast were the result of of an endosymbiosis with a bacterium and a cyanobacteria, respectively.

As time went on, these eukaryotes would evolve into animals and plants, the plants being the eukaryotes that formed an endosymbiosis with the cyanobacteria. Three eras marked important points the evolution of these organisms. One major event was the emergence of the first multicellular animals. Life before this consisted of only of invertebrate, spineless organisms. These vertebrae had several distinct advantages, including locomotion, bilateral symmetry, and a front side and back side. Another major event was the rise and fall of the dinosaurs during the mesozoic era. The dinosaurs appearance was due to the atmosphere, which was rich with oxygen, despite the climate being typically hot and dry. Yet another major event was conquest of the mammals and flowering plants during the cenozoic era. The climate was cooler and mammals emerged as the largest terrestrial creatures.


Climate/Temperature: Whether an area is hot or cold, and by how much, greatly influences the kinds of species that live there. Furthermore, the climate dramatically changes over time.


Atmosphere: The types of gases and their amounts in the atmosphere have changed drastically through the years. As early as 2.4 billion years ago, the atmosphere hardly had any oxygen in it at all. But thanks to the appearance of photosynthetic plants and algae. Increasing oxygen levels in the atmosphere are related to the emergence of animals, the increasing size of animals, and the increasing number of anthropods.


Landmasses: As the earth became cooler, a large landmass started to build up and rise out of the ocean, creating land-based and water-based environments. Over the course of billions of years, this landmass split into two, and later, several large landmasses known as continents. The formation of these continents is known as continental drift.


Floods and Glaciation: Massive floods often have profound impacts on the organisms that live there. Even more dramatic is the impact glaciers have on the landscape. On a regular basis they move throughout the land, causing a profound change in the land and the kinds of species that live there. Glaciers are said to be remnants of the sheets of ice that completely covered the Earth 790 to 630 million years ago, according to Joesph Kirschvink's "Snowball Earth hypothesis".


Volcanic Eruptions: Lava and ash from volcanic eruptions can kill organisms and create islands. If the eruption is large enough, the ash could cloud up in the atmosphere, changing global temperatures and solar radiation levels for a while.


Meteorite Impacts: Large meteorites have often introduced new minerals to Earth, as well as alter the environment in various other ways.



B. Useful Materials





These articles provide an adequate description of the appearance of prokaryotes and eukaryotes, and theories as to how the eukaryotes emerged.

Prokaryotes are organisms whose cells do not have a nucleus. There are two major classifications of prokaryotes, bacteria and archaea. Prokaryotes appeared between 3.5 billion years ago and 3.0 billion years ago during the Archean Eon.

Eukaryotes appeared 1.8 billion years ago and 1.5 billion years ago during the Proterozoic Eon. Eukaryotes contain a nucleus and membrane-bound organelles. One theory for the origin of membrane-bound organelles is that they resulted from phagocytosis performed by prokaryotes. It is thought that the Great Oxygenation Event that occurred 2.4 billion years ago created an environment in which eukaryotes could flourish.




This article describes the four eons of geologic time:

  1. PRE-ARCHEAN EON (or HADEAN EON) - 4.6 to 3.8 Billion years

~4.6 BYA -- Formation of Earth and Moon (as indicated by dating of meteorites and rocks from the Moon)

  1. ARCHEAN EON - 3.8 to 2.5 Billion years

The eon of first life


  1. PROTEROZOIC EON - 2.5 Billion to 570 Million years

The eon of the first multicelled life


  1. PHANEROZOIC EON - 570 Million years to the Present

The eon of complex life




These incredibly scholarly articles provide examples as to how the environmental factors mentioned influence the coming and going or species.

Environmental changes can influence the emergence or disappearance of species in a number of ways. Changes in temperature can cause a species to migrate looking for temperatures more conducive to survival. By moving, an important part of the existing food chain may be removed from the remaining species. It is also possible that by removing a predator, one or more remaining species may overrun the ecosystem and cause the extinction of competitors. If the new location does not contain adequate food or living habitat, the migrating species may not survive.


Changing the timing of life-cycle events important to the survival of a species is another way in which environmental changes can cause the disappearance of species is by. An example of this is that species that use temperatures to trigger nesting, breeding, and or birthing season may find that food supplies inadequate if the food supply is reliant on number of hours of sunlight.

Another example of environmental changes impacting the emergence and disappearance of species is the Great Oxygenation Event. This event, considered one of Earth’s most significant climate events, resulted in large amounts of free oxygen building up in the atmosphere. This build-up of oxygen killed off large numbers of anaerobic bacteria and set the stage for oxygen breathing organisms to thrive.



This interesting page lists some major events from the major eons in the geological time scale.


ARCHEAN EON - 3.8 to 2.5 Billion years

First Life (Prokaryotes), photosynthesis – about 3.5 billion years ago


PROTEROZOIC EON - 2.5 Billion to 570 Million years

Eukaryotes - multicellular organisms – about 1.5 billion years ago

Cambrian Explosion, hard-bodied organisms – about 570 million years ago


PHANEROZOIC EON - 570 Million years to the Present

Ordovician Period - 1st fish vertebrates – about 500 million years ago

Millipedes - 1st land animals – 420 million years ago

Devonian Period (Age of Fishes) - about 400 million years ago

1st trees – about 370 million years ago

Mississippian Period - 1st amphibians – about 360 million years ago

Pennsylvanian Period - 1st reptiles – about 300 million years ago

Triassic Period (Age of Dinosaurs), 1st mammals – about 245 million years ago

Roaches and termites have evolved – about 230 million years ago

Jurassic Period, 1st birds – about 208 million years ago

Tertiary Period (Age of Mammals) – about 70 million years ago

End of Dinosaurs – about 65 million years ago

Primitive monkeys – about 50 million years ago

Proconsul, 1st apes – about 25 million years ago

Ramapithecus – about 10 million years ago

Chimpanzee & hominid lines diverge – about 8 million years ago

Hominid line begins – about 4 million years ago

Australopithecus walks upright – about 3.5 million years ago

Australopithecus afarensis (Lucy) makes stone tools – about 3.4 million years ago

1st use of fire for cooking – about 1.9 million years ago

Homo erectus, crafted tools – about 1.6 million years ago

Homo erectus migrates out of Africa – about 1 million years ago

1st artificial shelter, Europe – about 380,000 years ago

Neanderthals – about 230,000 years ago

Neanderthals – about 100,000 years ago


C. Primary Literature


Early cyanobacterial fossil record: preservation, palaeoenvironments and identification





Cyanobacterial fossils are one of the oldest group of organisms dating back to 3500 Ma ago. It has been shown that cyanobacteria has played a significant role in the evolution of plantetary primary production and as a predecessor to plastids in algae and plants. Questions still need to be answered such as did cyanobacteria survive better extinction than eukaryotes before later losing ground? Did genetic changes allow for cyanobacteria to evolve and adapt better than its competitors? Cyanobacteria gradually became more complex and diverse but maintained its morphology to adapt. New analytical techniques have integrated which added information. Research in this field might explain these unanswered questions about the evolution of cyanobacteria.

This area of fossils is important because cynobacteria played a critical role. Long ago it was the main mechanism of the planetary primary production of organic matter which was the initial source of oxygen for the Earth. This allowed for photosynthesis and the proliferation of algae, green plants and animals. Cynobacteria can be free living or part of other eukaryotic phototrophic systems. These microfossils are preferably found preserved in growth position to analyze the surrounding populations of bacteria and sentiment.

Early fossil records are dominated by cyanobacteria because of a favorable environment or the role they played in being a primary producer. They could have been successful because of the ability to nitrogen fix that is critical in extreme environments. The fossil records cover a huge time period of 3500 million years. Diversity is thought to have played an important role in its abundance. However, cyanobacteria evolved very slowly compared to eukaryotes. There still needs to be much researched and understood about this important microfossil which might give scientists a better picture of the beginning of life on earth.


D. Virtual Lectures

Part 1 - Prokaryotes and Eukaryotes


Part 2 - Environmental Influences


Part 3 - Major Events in Evolution


Also disregard my comment at the end of the third, there was an error in my notes. During the quaternary period, many species of mammals, particularly the larger ones, went extinct, which is very significant.

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