Geologic Time Scale

1. Geologic Time Scale 8th science

2. Proof Organisms change over time • Fossils: prove that types of organisms on Earth have changed throughout history (ex. Dinosaurs) • Rocks: proof that the Earth’s plates have moved over time (example: there are sea shell fossils found in the rocks on Mt. Everest) • Ice cores: when scientists drill into polar ice caps, there is evidence that the climate has changed throughout Earth’s history (ex. Ocean temperature being raised as a result of global warming impacts the organisms living in the ocean.)

3. How has the Earth’s surface changed? • Earthquakes • Volcanoes • Erosion • Glaciers & Ice Ages • Meteor Impacts

4. What is the geologic time scale? • The appearance or disappearance of types of organisms throughout Earth’s history marks important occurrences in geologic time. • Paleontologists have been able to divide Earth’s history into time units based on the life forms that lived only during certain periods. • This division of Earth’s history makes up the geologic time scale.

5. Subdivisions of Geologic Time • The oldest rocks on Earth contain no fossils. • Later in Earth’s history came an explosion in the abundance and diversity of organisms. • These organisms left a rich fossil record.

6. Four Major Subdivisions • There are four major subdivisions of geologic time: • Eons: the longest subdivision based on the abundance of certain fossils • Eras: marked by major, striking, and worldwide changes in the types of fossils present • Periods: divide eras up into smaller units characterized by the types of life existing worldwide • Epochs: divide periods up into smaller units characterized by the type of life existing from continent to continent

7. Geologic Time Scale

8. Precambrian time • Precambrian time is the longest part of Earth’s history. • It includes the Hadean, Achaean, and Proterozoic Eons. • It last from 4.5 billion years ago to about 544 million years ago. • The oldest rocks on Earth have been dated to about 4 billion years ago, but they are rare. • There is relatively little known about the organisms that lived during this time. • The rocks are so deeply buried that they have been changed by heat and pressure and fossils cannot stand these conditions.

9. Paleozoic Era • Known as the “Era of Ancient Life” • Began just after the Precambrian Era, about 544 million years ago to about 248 million years ago • Many of the life forms discovered in this time were marine, living in the vast seas that covered the Earth. • Trilobites were common as well as other hard-shelled invertebrates (animals without a backbone). • Vertebrates (animals with backbones) were discovered in this era as well. • The first vertebrates to be discovered were fish-like creatures without jaws. • Some fish discovered in this time had lungs as well as gills, which indicates they could live on land as well as water. • Paleontologists believed amphibians might have evolved from fish with leg-like fins and lungs, and later in this era evolved into reptiles who no longer needed bodies of water to live and survive.

10. Paleozoic Era (con’t.) • The Appalachian Mountains formed during this time. • The formation of mountains occurred in several stages: • Volcanic Islands formed in the Atlantic were pushed against the coast of North America, while at the same time Africa moved toward North America. • The African plate collided with the North American plate, forming mountains on both continents. • About 200 million years ago the Atlantic Ocean opened, separating the two continents. • The end of this era is marked by 90% of all marine species and 70% of all land species having died off. • This mass extinction occurred because of changes in climate, a lowering of the sea level, or a catastrophic event. • The Permian Period, at the end of this era, is when it is suspected that the continental plates came together to form the supercontinent Pangaea.

11. Pangaea • It is believed that glaciers covered the southern part of Pangaea. • The gradual collision of the continents caused mountains to form. • The seas closed and deserts spread over much of North America and Europe. • Many species could not adapt to these changes which led to the mass extinction and the end of the era.

12. Mesozoic Era • Also called the “era of middle life” • All the continents were still joined together as Pangaea • During the Triassic Period Pangaea separated into two landmasses called Laurasia and Gondwanaland. • Later these two landmasses separated into the continents we know today. • The animals that survived the mass extinction at the end of the Paleozoic Era adapted to the changing environments, believed to much drier in the Mesozoic Era.

13. Mesozoic Era: Dinosaurs • The Mesozoic Era is the age of the dinosaurs, specifically beginning in the Triassic Period with small dinosaurs. • The Jurassic and Cretaceous Periods saw larger dinosaurs. • The dinosaurs continued to evolve, adapt and some became extinct during this era. • Paleontologists study fossilized foot prints to calculate how fast dinosaurs walked/ran. • They also study their bone structure and some evidence suggests some species of dinosaurs were actually warm-blooded like modern day mammals.

14. Mesozoic Era: Mammals • The first mammals appeared during the Triassic Period. • The earliest mammals are believed to be small mouse-like creatures. • Remember a mammal is a warm-blooded animal that has hair covering its body, feed their young with milk produced by the mother’s body, and are vertebrates.

15. Mesozoic Era: Birds • Birds first appeared in the Jurassic Period. • Some paleontologists believed birds evolved from small, meat-eating dinosaurs. • The earliest bird, Archaeopteryx, had wings and feathers. • BUT, paleontologists cannot confirm this dinosaur bird is a direct descendent of modern day birds because it also had features not associated with today’s birds.

16. Mesozoic Era: Angiosperms • Angiosperms are flowering plants. • They first evolved during the Cretaceous Period. • Angiosperms produce seeds with hard outer coverings which protect them allowing the angiosperms to live in many environments. • Today angiosperms are the most abundant and diverse plants alive. • Modern day angiosperms include magnolia and oak trees.

17. Mesozoic Era: end • The Mesozoic Era ended approximately 65 million years ago with a mass extinction of land and marine animals. • Many groups of animals, including the dinosaurs, disappeared suddenly. • Paleontologists believe a comet or asteroid collided with the Earth, creating a huge cloud of dust and smoke that blocked the sunlight from reaching the Earth’s surface. • Without sunlight, all the animals and plants that rely on it died. • There is a crater in Mexico and worldwide deposits of ash and iridium (element found in asteroids) that support this hypothesis.

18. Cenozoic Era • Also called the “era of recent life” • This is the era we are currently living in and spans back 65 million years ago. • Many mountain ranges in North and South America and Europe began to form. • The ice ages occurred during this era. • Homo sapiens (or humans) appeared approximately 140,000 years ago and may have caused the extinction of other mammals because early evidence suggests early humans were hunters and competed for food.