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Scientists have developed a model of the history of life on Earth called the

Scientists have developed a model of the history of life on Earth called the geologic time scale . The geological time scale is based on studies of Earth’s geology and the fossil record . Earth’s Geologic Time Scale. • Most of Earth’s changes have occurred

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Scientists have developed a model of the history of life on Earth called the

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  1. Scientists have developed a model of the history of life on Earth called the geologic time scale. • The geological time scale is based on studies of Earth’s geology and the fossil record.

  2. Earth’s Geologic Time Scale • Most of Earth’s changes have occurred slowly, over millions of years. • But some times, Earth’s history has been affected by catastrophes such as massive volcanic eruptions or meteor hitting • These events had a HUGE effect in shaping Earth’s surface and on the evolution of life.

  3. Divisions of the Geologic Time Scale • Paleontologists divide the geologic time scale into different blocks of time. • Largest blocks of time or eons. • Eons are then divided down into smaller blocks of time called eras & periods. • The smallest blocks of time are called epochs. • Eons Eras Periods Epochs

  4. Eons Eras Periods Epochs

  5. Precambrian time 4.6bya-544mya

  6. Precambrian Time • Precambrian Time makes up 88% of Earth’s history, but little is known. • Earth formed 4.6 bya • At first oxygen was absent from the atmosphere. • 1st life forms were single celled, like cyanobacteria. • Oceans formed • 1st invertebrates (Most life forms were soft-bodied)

  7. Precambrian Time • Meteorites crashed on Earth and radiation from the sun bombarded our planet. • Thunderstorms and volcanic eruptions were nonstop. • *After photosynthesis started, oxygen becomes a major gas in Earth’s atmosphere. (bacteria, not plants started using Photosynthesis)

  8. Paleozoic Era (ancient life) 544-245mya

  9. Paleozoic Era (ancient life) • Lots of organisms with hard parts, like shells • Warm, shallow seas covered most of Earth • Lots of marine (sea) organisms • 1st vertebrates appear • 1st land organisms appear • Many mountains formed (Appalachians) & rocks of our continents form! • Pangaea forms • Mass extinction (90% sea life and 70% all life on land)

  10. Mesozoic Era Middle Life 245-65mya

  11. Mesozoic Era (middle life) • Also known as the Age of Reptiles or Dinosaurs • Dinosaurs are the most well-known reptiles of the Mesozoic era and dominated Earth for about 150 million • Tectonic plates were moving VERY fast during this era. • Pangaea breaks apart.

  12. Mesozoic Era (Age of the Reptiles) • 1st birds • 1st mammals (small, mouselike animals) • 1st flowering plants • At the end of the Mesozoic era, 65 mya, geologic evidence indicates that a giant meteor hit Earth creating a humongous dust cloud and worldwide fires.

  13. Cenozoic Era (Recent Life) 65mya-today

  14. Cenozoic Era65mya-today • Fossils from the Cenozoic era are closest to Earth’s surface, making them easier to find. • Therefore, scientists have the most fossil evidence from this era • Earth’s climate cooled& Ice Ages happened! • Mammals evolved adaptations that allowed them to live in many different environments (on land, in water, & in the air)

  15. Cenozoic EraAge of the Mammals • Alps, Andes, & Himalayan Mountains formed • Fossil record suggests that human ancestors first appeared about 4mya (Homo sapiens OR modern humans about 140,000 years ago)

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