Volcanoes and Igneous Activity Earth - Chapter 4

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Chapter 13
Earths History
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13.1 Precambrian Time Vast and Puzzling

• The Precambrian
• encompasses immense geological time
• From Earths distant beginnings 4.56 billion
  years ago until the start of the Cambrian period,
  over 4 billion years later.

? Precambrian Rocks
Shields - large, relatively flat expanses of
ancient metamorphic rock within the stable
continental interior.
Most of our knowledge about Precambrian rocks
comes from ores mined from shields.
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Geologic Time Scale
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Remnants of Precambrian Rocks
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13.1 Precambrian Time Vast and Puzzling
? Earths Atmosphere Evolves
The original atmosphere - gases like those
released in volcanic eruptions todaywater vapor,
carbon dioxide, nitrogen, and several trace
gases, but NO OXYGEN.
Later on, primary plants evolved using
photosynthesis, and oxygen was released. (Iron
mopped up a lot of this early oxygen)
Oxygen began accumulating in the atmosphere
about 2.5 billion years ago.
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13.1 Precambrian Time Vast and Puzzling
? Precambrian Fossils
The most common Precambrian fossils are
stromatolites.
Stromatolites distinctively-layered mounds
or columns of calcium carbonate. They are not the
remains of actual organisms but are the shell
material deposited by algae called diatoms
Many of these ancient fossils are preserved in
cherta hard dense chemical sedimentary rock.
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13.2 Paleozoic Era Life Explodes

• Following the long Precambrian, the most recent
  540 million years of Earths history are divided
  into three eras
• 1) Paleozoic(oldest)
• 2) Mesozoic (middle)
• 3) Cenozoic (newest).

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13.2 Paleozoic Era Life Explodes
? Early Paleozoic History
During the Cambrian, Ordovician, and Silurian
periods, the vast southern continent of Gondwana
encompassed five continents (South America,
Africa, Australia, Antarctica, and part of Asia).
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Gondwana and the Continental Landmasses
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13.2 Paleozoic Era Life Explodes
? Early Paleozoic Life
Life in early Paleozoic time was restricted to
the seas. - Life in the Paleozoic is split into
7 periods - Cambrian - Ordovician -
Silurian - Devonian - Mississippian -
Pennsylvanian - Permian
Invertebrates
Fishes
Amphibians
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Life in the Ordovician Period
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13.2 Paleozoic Era Life Explodes
? Late Paleozoic History
Laurasia is the continental mass that formed
the northern portion of Pangaea, consisting of
present-day North America and Eurasia.
By the end of the Paleozoic, all the
continents had fused into the supercontinent of
Pangaea.
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Late Paleozoic Plate Movements
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13.2 Paleozoic Era Life Explodes
? Late Paleozoic Life
400 million years ago, plants adapted to
survive at the waters edge and began to move
inland, becoming land plants.
The amphibians rapidly diversified because
they had minimal competition from other land
dwellers.
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Armor-Plated Fish
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Model of a Pennsylvanian Coal Swamp
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13.2 Paleozoic Era Life Explodes
? The worlds climate became very seasonal,
probably causing the dramatic extinction of many
species.
? The late Paleozoic extinction was the greatest
of at least five mass extinctions to occur over
the past 500 million years.