Earths History The Earth is estimated to by

Earth’s History The Earth is estimated to by around 4. 5 billion years old. – Most information about the age of the Earth comes from studying the rocks in the crust. – We can aso study fossils. • Explore the following link for more info on fossils: http: //www. ucmp. berkeley. edu/education/explorations/tours/fossil/guide. html

Rocks

Evidence of Change Life • • • Fossils Ice cores Composition of sedimentary rocks Faults Igneous rock formations

Fossils • provide important evidence of how life and environmental conditions have changed • the preserved remains or traces of an organism that lived in the past • different types of fossils based on how they were formed

Types of Fossils • Mold fossil – forms when sediments bury an organism and the sediments change into rock; the organism decays leaving a cavity in the shape of the organism • Cast fossil – forms when a mold is filled with sand or mud that hardens into the shape of the organism.

Types of Fossils • Petrified fossil (permineralized fossil) – forms when minerals soak into the buried remains, replacing the remains, and changing them into rock. • Preserved fossil – forms when entire organisms or parts of organisms are prevented from decaying by being trapped in rock, ice, tar, or amber

Types of Fossils • Carbonized fossil – forms when organisms or parts, like leaves, stems, flowers, fish, are pressed between layers of soft mud or clay that hardens squeezing almost all the decaying organism away leaving the carbon imprint in the rock. • Trace fossil – forms when the mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind.

Ice Cores • Ice cores- cylinders of ice that are drilled out of glaciers and polar ice sheets. • When snow falls it carries with it the compounds that are in the air at the time. • A record of the atmosphere at the time that the snow creating the ice layers fell.

Sedimentary Rock • 75% of the rocks on the Earth’s surface. • form on the surface of the Earth, anywhere that sand, mud, or other types of sediment collect. • Scientists can gain an understanding of Earth’s climate, biological, and geologic history by examining the contents of different layers of sedimentary rock.

Principles of Stratigraphy 1. Uniformitarianism The processes that formed rocks in the past are the same as those we observe on Earth today.

Principles of Stratigraphy 2. Law of Original Horizontality Sediments are deposited in horizontal layers that are parallel to Earth’s surface. Geological processes change the angle AFTER the rocks have been deposited.

Principles of Stratigraphy 3. Law of Superposition The oldest layers of rock are on the bottom. The youngest are on top.

Principles of Stratigraphy 4. The Law of Cross-Cutting Relationships Any igneous rock or fault must be younger than the rock layer it is in.

Principles of Stratigraphy 5. Unconformities Gaps in the rock record. Formed when part or all of a layer is missing.

Principles of Stratigraphy 6. Correlation The matching of rock layers from different locations. • Index fossils are fossils that are known to come from a specific time period. (Very useful in correlating rocks on different continents)

Igneous Rock • Sedimentary rock layers can be disturbed by igneous rock when molten rock forces it way up through the layers above it. • Sedimentary rock layers must be there first, so igneous rock intrusions are younger • Igneous rock is always younger than rock layers it cuts through.

Faults • a break in the rocks that make up the Earth’s crust that is formed due to the movement of rock on either side of the fault • two main types of faults involve dip slips and strike slips.

Dip Slips • two pieces of land change their vertical position compared to one another • one side of the fault is higher than the other Strike Slips -two pieces of land move horizontally

Two Ways to Determine Rock Age 1. Relative dating-compares ages of different rock layers and fossils. 2. Absolute dating gives the actual age of the rock. Radioactive dating-used for absolute dating.

Radioactive Dating • Radioactive decay- unstable elements in the Earth’s crust will decay into smaller elements at a constant and predicable rate – The half-life-time it takes for one half of a sample to decay.

Radioactive Dating • Since radioactive decay is constant, amounts of original and decayed elements are compared. • Determines the age of the substance. • Parent atom = radioactive • Daughter atom = stable atom

Relative Dating • The Earth’s surface has changed over time. • Geologist’s use the rock record to interpret past events. • Stratigraphy -study of structure, fossil content, origin, history, and age relationships of rock formations.

Plate Techtonics • The movements of Earth’s continental and oceanic plates have caused mountains and deep ocean trenches to form and continually change the shape of Earth’s crust throughout time. • Sea level changes over time have expanded and contracted continental shelves, created and destroyed inland seas and shaped the surface of land. • Sea level changes as plate tectonics cause the volume of the oceans and the height of land to change, as ice caps on land melt or enlarge and/or as sea water expands when ocean water warms and cools. • The evolution of Earth’s living things is strongly linked to the movements of the lithospheric plates. • The movements of the plates cause changes in climate, in geographic features such as mountains, and in the types of living things in particular places.

Geologic Time The geologic time scale is divided into eras marked by important events in the rock record. Eras can be divided into periods, and periods can be further divided into epochs. • Listed youngest to oldest

Geologic Time • Precambrian Era: – Oldest and Longest (about 4 billion years) – Little is known about this era. The Earth formed during this era, and the first life developed. • Paleozoic Era: – Organisms became more complex; Biodiversity exploded – The first mass extinction occurred at the end of this era. • Mesozoic Era: – Age of the Dinosaurs • Cenozoic Era: – Age of Mammals

What is the Earth’s time scale? • The Geological time scale is a record of the life forms and geological events in Earth’s history. • Scientists developed the time scale by studying rock layers and fossils world wide. • Radioactive dating helped determine the absolute divisions in the time scale.

Divisions of Geologic Time • Eras are subdivided into periods. . . periods are subdivided into epochs. Era Period Epoch E + P = EP

FOUR Eras… • PRECAMBRIAN – 88% of earth’s history • Paleozoic (ancient life) – 544 million years ago…lasted 300 million years • Mesozoic (middle life) – 245 million years ago…lasted 180 million years • Cenozoic (recent life) – 65 million years ago…continues through present day

Precambrian Era • 5 major events occurred during this era: 1. The formation of the Sun and light. Creation of 2. Earth 3. atmosphere through volcanic outgassing. 4. Oceans 5. Life

Precambrian Era • 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.

Paleozoic Era (Ancient Life) • The Cambrian period is the 1 st period of the Paleozoic Era. “Age of the Trilobites” • Explosion of life in the oceans began during this era. • Most of the continents were covered in warm, shallow seas. – Invertebrates were dominate - Trilobites – Fish emerged – Fish led to the arrival of amphibians • The end of the Paleozoic era is called the “Age of Amphibians” – Early land plants including mosses, ferns and cone-bearing plants. – The early coal forming forests were also formed during this time.

Trilobites • Lived in Earth’s ancient seas • Extinct before the dinosaurs came into existence • Cambrian Period is know as the “Age of the Trilobites” • Body has 3 sections • Good index fossil

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

Brachiopods • Marine animals that resemble clams.

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

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 plant-eaters die.

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: – 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.

Today… • Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic Era. Which unit is the largest? Which unit is the smallest?