1. Carlos Isaac Monsalvo Jasso #11 11A
Click on the name and you’ll be taken to the Era, feel free to click the periods and it
should take you there.
Paleozoic Era Cenozoic Era
Precrambian
Mesozoic Era

2. Precrambian Time
* It takes over 650 – 544 millions of years ago.
During this time, 90% of Earth’s history occurred
here.
* Anaerobic structures appeared with
photosynthetic methods, adding oxygen to the
atmosphere and allowing evolution.
*There are few fossils since animals were soft
bodied, and during this time life only existed in the
sea.
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3. Paleozoic Era
* This period was from 544 to 290 millions years ago.
* Early in the Paleozoic Era, fossil record became
rich with evidence of many types of marine life.
* This fossil evidence shows that life was highly
diverse by the first part of the Paleozoic Era.
* This era is divided into 4 periods: Cambrian
Period, Ordovician & Silurian Periods, Devonian Period
and Carboniferous & Permian Periods.
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4. Cambrian Period
* According to Paleontologists, this is the
period in which diversification of life
existed, “Cambrian Explosion”.
* In this period, organisms finally had hard
structures (shells and exoskeletons).
* In this period there were invertebrates like
jellyfishes which drifted through the
water, crawled in the surface or attached
themselves to ocean floors; trilobites were
common as well.
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5. Ordovician & Silurian Periods
* Fist vertebrates to appear were jawless
fishes. During these periods, the ancestors of
modern octopi and squid appeared.
* Some animals in this time grew to the length of
13M.
* During these periods, insects
appeared, plants evolved and grew low to the
ground in damp areas.
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6. Devonian Period
* Several plants during this period adapted to
drier areas, which enabled them to invade more
habitats.
* In this period many groups of fishes were
present in the ocean; and sharks appeared in the
later times.
* During the Devonian period, animals began to
invade the land. Some fish developed the ability
to crawl on leg like fins and eventually evolved
into amphibians.
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7. Carboniferous & Permian Periods
* During this period, life expanded over Earth’s
continents.
* Several animals evolved from amphibians (i.e.
reptiles).
* Remains of ancient plants formed deposits of
sediment that became coal.
* At the end of the Paleozoic era, many organisms
died due to a mass extinction: 95% of the complex
life in oceans disappeared.
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8. Mesozoic Era
* It lasted about 180 million years ago.
* During this period there was an increasing
dominance of dinosaurs. The Mesozoic Era is
marked by the appearance of flowering plants.
* This Era was divided into three periods: Triassic
Period, Jurassic Period and Cretaceous Period.
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9. Triassic Period
* Organisms that survived the mass extinction
became the main forms of life early in this
period.
* Important organisms that survived:
fishes, insects, reptiles and cone bearing plants.
This era is commonly called “Age of the Reptiles”.
* About 225 million years ago, the first dinosaurs
appeared, and the first Mammals appeared at late
Triassic period, which resembled mouse or shrew.
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10. Jurassic Period
* Dinosaurs became the dominant animals on land in
this period.
* Dinosaurs “ruled” for about 150 million years but
there were different types in different times.
* One of the first birds appeared during this
time, which made paleontologists think that birds
are relatives of dinosaurs.
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11. Cretaceous Period
* Reptiles still were the dominant vertebrates
throughout this period.
* Meat eating dinosaurs dominated land
ecosystems, while flying reptiles and birds soared
the sky.
* The Cretaceous period brought new forms of
life: leafy threes, shrubs, and small flowering
plants which produced seeds.
* There was another mass extinction, which wiped
half of all plant and animals groups, including
dinosaurs.
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12. Cenozoic Era
* This era lasts from 65 million years ago to
present days.
* During this era, early mammals competed with
dinosaurs for food and places to live.
* During the Cenozoic era, mammals evolved
adaptations that allowed them to live in various
environments.
* This era is often called the “Age of Mammals”.
* This era is divided into two periods: Quaternary
Period & Tertiary Period.
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13. Tertiary Period
* Earth’s climate was warm and mild.
* In oceans, marine mammals like whales and
dolphins evolved; on land, flowering plants and
insects flourished, providing food source for
grazing mammals.
* Some mammals became very large during this
period.
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14. Quaternary Period
* Mammals that had evolved in the Tertiary
Period had to face a changing environment during
this period.
* In this period, Earth’s climate went into a series
of ice ages.
* About 20.000 years ago Earth’s climate began
to warm up, melting glaciers over time.
* During this time, the Homo Sapiens might have
evolved as early as 100.000 years ago in Africa.
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