The Geologic Time Scale . . Video: Land Formation Geologic Time Scale Geologic Time Scale: the record of the life forms and geologic events in the Earth’s history. Since the span of time is so great from the formation of the Earth to now, scientists can’t use a normal calendar to describe times. Geologic Time Scale Cenozoic Era 65mya The geologic time Mammals scale is broken into Mesozoic Era 248mya 4 eras. These are Reptiles characterized by the type of animal Paleozoic Era 540mya that dominated that Amphibians period of time. Precambrian 4.6bya Video: Geologic Time Scale Single celled to none Extinctions Extinct: When an animal or plant species dies out completely. Mass Extinction: When a large number of species dies out at the same time. Video: Extinction Reasons for Extinctions Movements of continents. Meteorites hitting the Earth. Ice ages. Major changes in the climate. The Four Eras Scientists have divided the geologic history into four eras. – Precambrian Time. – Paleozoic Era. – Mesozoic Era. – Cenozoic Era. Precambrian Time Precambrian Time: 540 mya to the beginning of the Earth. Only very prehistoric organisms lived. Baicalia= bacteria The Early Earth Scientists hypothesize that Earth was a place of great chaos. Meteorites crashed into Earth. Constant violent thunder storms. Volcanic eruptions. Intense radiation from the sun. The Early Earth Video: Precambrian How Life Began Scientists hypothesize that life developed 3.5 billion years ago from nonliving matter that already existed. This matter included water, clay, minerals in the ocean and gases in the atmosphere. The energy present in the early Earth caused these chemicals to react and form DNA like material. Early Life Bacteria Life Evolves For millions of years these DNA like molecules floated in the oceans reacting with each other to make more complex molecules. The reactions of these molecules may have led to the first cells, prokaryotic. Prokaryotic Cells Prokaryotic Cells: cells without a nucleus. Oxygen=Pollution? Early life did not need oxygen to survive. They made their own food from carbon dioxide through photosynthesis and gave off oxygen as waste. Evolution Again? As the atmosphere took on more oxygen, it formed a shield to protect Earth from the sun’s rays called the ozone layer. This helped keep oxygen in the air and allowed early life to evolve to breathe the oxygen in the air. These new organisms are now called eukaryotes, or cells with a nucleus. Eukaryotes The first eukaryotes evolved over 2 billion years ago. Nucleus Prokaryote Eukaryote Paleozoic Era Paleozoic Era: 248mya-540mya, means “ancient life”. Rocks from this era are rich in fossils of animals such as sponges, corals, snails, clams, squids, trilobites, and early fish and sharks. Paleozoic Era The Paleozoic era begins with the Cambrian Explosion, in which many different kinds of organisms evolved. The Cambrian Explosion was a time of a great number of new species evolving. Paleozoic Life Snails Corals Sponges Clams Squids Trilobites Video: Paleozoic Era During the Paleozoic Era, plants, fungi, and air-breathing animals colonized dry land. Plants provided the first land animals with food and shelter. Giant Ferns Conifers Horsetails Fossils indicate that crawling insects were some of the first land animals. Near the end of the era, reptiles, winged insects, cockroaches, and dragonflies appeared. Reptiles Dragonflies Cockroaches Permian Extinction The largest mass extinction known occurred at the end of the Paleozoic era, about 90% of all marine species died out. Video: Ice Age Mesozoic Era Mesozoic Era: 65mya-248mya, means “middle life”, also called the age of reptiles. After the Paleozoic mass extinction scientists think there was a burst of evolution resulting in many new and different species. Video: Mesozoic Era Mesozoic Life Birds Flowers Dinosaurs K-T Extinction K-T Extinction: At the end of the Mesozoic era, an asteroid is believed to have hit the earth causing a mass extinction. It is believed a large asteroid hit the Earth, caused dust to block the sun killing all of the plants, the animals had nothing to eat so they died. Temperatures also dropped very low. Song: Do The Dinosaur Video: Extinction Cenozoic Era Cenozoic Era: 65mya-now, means “recent life”, also called the age of mammals. We have the most fossil information from this era because the fossils from this era are closest to the surface. Video: Cenozoic Era Cenozoic Life Saber-toothed Cat Camels Mastodon and Cro-Magnon man Cenozoic Life Modern humans or Homo sapiens may have evolved as early as 100,000 years ago.