The Geologic Time Scale Began When Earth Was Formed and Goes on Until the Present. at The
11,000 years ago-present / Modern humans appear
65-54 million years ago / Mammals become abundant
146-65 million years ago / Flowering plants
208-146 million years ago / Birds take flight
245-208 million years ago / First dinosaurs and small mammals
360-286 million years ago / First reptiles to live only on land
410-360 million years ago / First amphibians develop
440-410 million years ago / First insects appear on land near the water’s edge
505-440 million years ago / First fish develop
544-505 million years ago / Explosion of multi-celled organism in the oceans
2500-544 million years ago / First muliticelled life forms in the oceans
3800-2500 million years ago / Single celled organisms form in the oceans
Geological Time Scale
Follow Up:
The geologic time scale began when Earth was formed and goes on until the present. At the end of each era a mass extinction occurred, many kinds of organisms died out, although there were other extinctions going on during each period of geologic time. Using the fossil record, paleontologists have created an idea of the different types of common organisms in each geologic period.
1. Infer: After a mass extinction of 90% of all organisms died. How did this benefit the organisms that survived?
o Precambrian Era
§ The Precambrian Era is Earth's first era of time. It began with the creation of the Earth around 4.6 billion years ago.
§ 5 major events occurred during this era: (1) the formation of the Sun and light, (2) the creation of the Earth, (3) the creation of the atmosphere through volcanic out-gassing, (4) the creation of the oceans, and (5) the creation of life.
§ Began with simple life forms such as bacteria and simple algae.
§ There was a rise of simple organisms such as jellyfish and sea worms by the end of the era.
§ Few fossils because the life forms were soft-bodied and had no hard skeleton.
2. Why did simple life forms like bacteria and jelly fish evolve first? Think back to the structure of bacteria.
3. Explain in detail relating back to how a fossil forms and explain why very little fossil types survive this era?
o Paleozoic Era
§ Began with the early invertebrates (organisms with no spine), such as trilobites and brachiopods; continued to develop
§ then early vertebrate (with spines) fish,
§ then Arachnids (spider like) and insects developed
§Later came the first amphibians, and near the era’s end the reptiles became dominant.
§ Early land plants included simple mosses, ferns, and then cone-bearing plants.
§ By the end of the era, seed plants were common.
§ The mass extinction that ended the era caused most marine invertebrates as well as amphibians to disappear.
1. Why did invertebrate organism develop before vertebra organisms?
2. Why were early plants very small and simple?
o Mesozoic Era
§ Reptiles were the dominant animals of this era, including the various dinosaurs.
§ Small mammals and birds also appeared.
§ Toward the end of the era, flowering plants appeared and the some types of mammals increased.
§ The mass extinction that ended the era caused the dinosaurs to become extinct. Most likely a severe climatic change event caused a dramatic drop in temperature.
1. Why were reptiles able to become the dominate species after a majority of the amphibians died?
2. Why did mammals remain small during this era?
3. Why did birds evolve so late in Earth’s history?
o Cenozoic Era
§ New and larger mammals appeared while others became extinct.
§ The diversity of life forms increased.
§ Flowering plants became most common.
§ Humans are also part of the most recent period of this era.
1. Why were larger mammals and humans able to develop during this era?