Geologic History A Journey Through Time

How long do you think it took to form the Grand Canyon?

How old is the Earth? Scientists have determined the age of the Earth to be about 4.55 billion years old. (4.6*10 9 y.a.) 4.6 b.y. is a tremendous amount of time. So long in fact that humans have only been around for 0.035% of the Earth’s history.

Geologic Time “The study of geologic time allows us to reconstruct Earth’s history, gaining a sense of the world before humans and allow us to possibly predict events and conditions of the future.”

Geologic Time Scale The geologic time scale is a chronological model of the geological history of Earth using divisions of eons, eras, periods, and epochs.

These graphics show how Precambrian time relates to the whole of time. Special note- oxygen was added to our atmosphere after organisms that could use photosynthesis to live evolved. After that more complex cells evolved- oxygen is necessary to carry out complex life processes in larger more organized cells- eukaryotes.

Geologic History of the Earth “in a Nutshell”

Origins of our Solar System

Creation of the Earth

Earth’s Formation Earth formed through the gravitational attraction and accumulation of asteroids and rocky debris This accretion of material generated a tremendous heat causing the planet to be molten The denser materials settled into the interior and the Earth’s layered internal structure formed.

Variations in Fossils and Environments Evidence from the fossil record (preserved in sedimentary rocks) shows that a wide variety of life forms have lived in Earth’s changing environments over time.

Variations in Fossils and Environments The comparisons of fossil remains and current life forms enable scientists to make predictions about the Earth’s past environment. A major reason for changes in Earth’s environment over geologic time has been the movements of plates and their associated landmasses.

The theory of organic evolution states that life forms change through time. As environmental conditions change, variations within a species give certain individuals a greater chance for surviving and reproducing. These variations, along with others get passed on to future generations leading to the creation of a new species. Fossils and the Evolution of Life s

Rates of Evolution The fossil record provides evidence for the theory of organic evolution. This also shows that evolution does not always occur at the same rate. There are times of rapid extinctions and subsequently rapid evolution of new species.

Rates of Evolution An impact event, such as the collision of a comet or asteroid with Earth, may cause catastrophic environmental changes leading to rapid extinctions and evolutions. Such an event probable occurred at 65 m.y. and is associated with a massive extinction of roughly 70% of the Earth’s species.

Life On Earth Throughout Geologic Time Precambrian (4.6 b.y m.y.) – Simple organisms (invertebrates) – “Soft-Bodied” Organisms (Fossils are rare)

Stromatolites Formed from the trapping of sediment in layers by Blue-Green Algae (Cyanobacteria)

Life On Earth Throughout Geologic Time Paleozoic (540 – 245 m.y.a.) –Organisms proliferate and become more complex (vertebrates) –Shelled (mineralized skeletons and shells) organisms develop –(Brachiopods/Trilobites) –Amphibians develop from lobe-finned fish –Era ends with a mass extinction killing off more than 95% of the life on earth

Cambrian Life

Eurypterid (Sea Scorpion) Fossil

Eurypterid in Action

Devonian Life

Phacops Trilobite of the Devonian

Carboniferous Forests – formed extensive coal deposits

Evolution of Amphibian from Lobe-Finned Fish (Devonian)

Mesozoic Life ( mya) – “Age of Reptiles” (dinosaurs, flying reptiles and birds develop) – Modern fauna begins to develop on land – Era ends with a mass extinction killing off dinosaurs, ammonoids, flying reptiles, and some swimming reptiles. Life On Earth Throughout Geologic Time

Triassic Plateosaurs

Iguanodons

Cretaceous T-Rex

Life On Earth Throughout Geologic Time Cenozoic Life (65 m.y.a. – present) – “Age of Mammals” (mammals begin to develop and evolve) – Humans develop from primates (Homo Habilus 1.6 m.y.)

Early Hominids Mastodonts