Scientists have developed a model of the history of life on Earth called the geologic time scale....
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Transcript of Scientists have developed a model of the history of life on Earth called the geologic time scale....
• Scientists havedeveloped a model of the history
of life on Earth called thegeologic 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 occurredslowly, over millions of years.• But some times, Earth’s history has been affected by catastrophes such asmassive volcanic eruptions or meteorhitting• These events had a HUGE effect inshaping Earth’s surface and on theevolution of life.
Divisions of the Geologic Time Scale
• Paleontologists divide the geologic timescale 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
Eons Eras Periods Epochs
PRECAMBRIAN TIME4.6BYA-544MYA
Precambrian Time• Precambrian Time makes up 88% of Earth’s
history, but little is known.1. 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)
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 usingPhotosynthesis)
PALEOZOIC ERA(ANCIENT LIFE)
544-245MYA
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 and70% all life on land)
Mesozoic EraMiddle Life
245-65mya
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.
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 giantmeteor hit Earth creating a humongous dust
cloud and worldwide fires.
Cenozoic Era(Recent Life)
65mya-today
Cenozoic Era65mya-today
• Fossils from the Cenozoic era are closest toEarth’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)
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)