The Geologic Time Scale

So far… Up to this point in Unit 1 we have talked about: Formation of the Sun, Planets and Earth (Notes 1) How our planet was structured during formation (Notes 2) Most recently we have discussed Earth’s history and the methods we use for putting together the story of our planet.

So Far… What is the method we used to put layers and events in order from oldest to youngest? What is the method we used to figure out if layers found in different regions were the same or different? What is the method that we used to put real ages with the layers and events? How long have we had the ability to do this?

Geologic Time Scale Think about all the units of time we use to measure events in our daily lives. What are they? What units would you use to describe the length of the following events? Sneezing Vacation Class Baseball Game Life Would it make sense to describe a sneeze in years?

Geologic Time Scale The story of Earth’s history is full of events that have taken an extremely long time to an incredibly short time. Because Earth’s history is so much larger than what humans operate on, we need more units.

Geologic Time Scale Largest Smallest Eon Era Period Epoch Age EON eON is ON top “E” “P” “E” + “P”= “EP” Your age is small

Geologic Time Scale The largest division in the time scale. There have only been 4 Eons. They are so large they are not really useful to talk about. We are in the Phanerozoic Eon that contains all non- microscopic life. The first three Eons (Hadean, Archaean, Proterozoic) took the first 4 billion years! Because the first three contain either no life or at the end microscopic life they are referred to together as the Precambrian.

Eras The coolest subdivision of the time scale! The three Eras of the Phanerozoic are all separated by catastrophic extinction events.

Eras Paleozoic Era (ancient life): lasted about 300 million years. Beginning was marked by the appearance of non- microscopic life. Invertebrates Vertebrates (armored fish) Land Plants Fish Trees Amphibians Reptiles

Paleozoic Era Much of the limestone quarried for building and industrial purposes, as well as the coal deposits of western Europe and the eastern United States, were formed during the Paleozoic. The Cambrian (beginning) opened with the breakup of the world-continent Rodinia and closed with the formation of Pangaea, as the Earth's continents came together once again. This event is thought to have caused the climate changes that led to mass extinction event. The Appalachian mountains were formed during this time.

Paleozoic Era At the end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species and 70% of land animals. Possible causes of this Mass Extinction Event Lowering of sea levels when the continents were rejoined as Pangaea (convergent boundary) Increased volcanic activity (ash and dust) Climate changes – cooler climate

Trilobites Lived in Earth’s ancient seas Extinct before the dinosaurs came into existence Cambrian Period is known as the “Age of the Trilobites”

Brachiopods Marine animals that resemble clams.

Early Fish Early fish did not have jaws. Some species of sharks were in existence at this time.

Frilled Shark that was found in Japan in January 2007 Frilled Shark that was found in Japan in January 2007. This shark was considered a “living fossil”

Early Land Plants Mosses Cone bearing plants Ferns

Mesozoic Era – Middle Life At the beginning of this era the continents were joined as Pangaea. Pangaea broke up around the middle of this era. Reptiles became the most abundant animals because of their ability to adapt to the drier climate of the Mesozoic Era. Skin maintains body fluids Embryos live in shells

Mesozoic Era Dinosaurs were also very active in this era. First small dinosaurs appeared in the Triassic Period. Larger and more abundant dinosaurs appeared in the Jurassic Period. Small mammals and birds also appeared during this era. The mammals were small, warm-blooded animals. Hair covering their bodies. These characteristics help them survive in changing environments.

Mesozoic Era The main plant life of this time were Gymnosperms or plants that produce seeds, but no flowers. Pine Trees Flowering plants appeared during the END of this era.

Mesozoic Era This era ended with a mass extinction event about 65 million years ago. Many groups of animals, including the dinosaurs disappeared suddenly at this time. Many scientists believe that this event was caused by a comet or asteroid colliding with the Earth.

Mesozoic Era – Mass Extinction Event Asteroid or Comet collides with Earth. Huge cloud of smoke and dust fills the air Blocks out sunlight Plants die Animals that eat plants die Animals that eat plant-eaters die. However, not all forms of life died during this event. Many animals that you see today are descendants from the survivors of this extinction event.

Dinosaurs

Mesozoic Reptiles

Mesozoic Mammals

Mesozoic Plants Flowering plants evolved towards the end of the Mesozoic Era.

Cenozoic Era – Recent Life Began about 65 million years ago and continues today!!!!! Climate was warm and mild. Marine animals such as whales and dolphins evolved. Mammals began to increase and evolve adaptations that allowed them to live in many different environments – land, air and the sea. Grasses increased and provided a food source for grazing animals Many mountain ranges formed during the Cenozoic Era Alps in Europe and Himalayas in India; Rocky Mountains in the USA

Cenozoic Era Growth of these mountains may have helped to cool down the climate Ice Ages occurred late in the Cenozoic Era (Quaternary Period). As the climate changed, the animals had to adapt to the rise and fall of the oceans caused by melting glaciers. This era is sometimes called the “Age of Mammals”

Cenozoic Era Marine animal examples: Land animal examples: Algae, Mollusks, Fish and Mammals Land animal examples: Bats, Cats, Dogs, Cattle and Humans Humans are thought to have appeared around 3.5 million years ago (during the most recent period – Quaternary). Flowering plants were now the most common plant life.

Cenozoic Mammals

Flowering Plants were common during the Cenozoic Era

Summary Geologic Time Scale requires larger units of time Units of time are Eons – Eras- Periods – Epochs – Ages Eons: Precambrian contains no or microscopic life Phanerozoic contains non-microscopic life (us!) Eras: Each are marked by an explosion of different life and ended with mass extinctions Paleozoic: Age of Trilobites Mesozoic: Age of Dinosaurs Cenozoic: Age of Mammals