Download 13.1 Precambrian Time

13.1 Precambrian Time
-Earth formed 4.56 b.y.a. (billion
years ago)
-atmosphere formed
-ocean formed
-tectonic plates began to build up
continental land
Earth Forms
-Gravity pulled dust, rock, & ice in
-Gravity increased, pulling in more of these
-High-velocity impact of rocks from space
caused planet to melt
-Dense materials (iron & nickel) sank
toward center (core)
-Less dense materials (silicates) “floated”
forming layers (mantle & crust)
Atmosphere Evolves
-Earth’s original atmosphere was
similar to gases released in volcanic
eruption: water vapor, carbon dioxide,
nitrogen, & trace gases (NO oxygen)
-Earliest life forms began to change
atmosphere by using carbon dioxide
and releasing oxygen
-Slowly OXYGEN increased
Oceans Form
-As planet cooled, water vapor
condensed to form clouds and great
rains began
-This sped up the cooling of Earth’s
surface
-Torrential rains slowly filled low areas
= OCEANS
Continents Develop
-mantle convection drove the process of plate
tectonics
-Rock Cycle began
-early continents were granitic igneous
rocks
-weathering & erosion led to
sedimentary rock formation
-tectonic forces & volcanic activity
helped form metamorphic rock
Shields
-large, relatively flat expanse of
ancient metamorphic rock within the
stable continent interior
-shaped like a warrior’s shield
Precambrian Life
-earliest life probably evolved in
oceans
-near hydrothermal vents
-one-celled organisms evolved that
use photosynthesis (Prokaryotes)
-similar to cyanobacteria
-photosynthesis- use CO₂ and
sunlight to make food (carbohydrates)
Stromatolites
-trace fossils left by cyanobacteria
(Precambrian time)
-are layered mounds of calcium carbonate
deposited by cyanobacteria
Prokaryotes & Eukaryotes
-Prokaryotes- cell that lacks a nucleus
-one celled
Eukaryotes
- Cells that have a nucleus
-more complex multi-cellular organisms
evolved
Eukaryotes with soft bodies evolved.
-can be multi-cellular
Multicelled Organisms
Ediacaran fossils (Australia)
-molds and casts of soft bodied animals
-resemble worms, jellyfish, coral
*To be preserved as fossils, they must
have been rapidly buried in fine sediment