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Geological Eras
Montana History
Precambrian Era
4.6 billion – 544 million
years ago
First one-celled
creatures
Montana covered by
a large sea
Covers almost 90% of
the history of Earth
Precambrian Continued
 Different
layers of
sedimentary rock were
settled over millions of
years, creating layers in the
Earth
 Within these layers, we find
fossilized remains of plants
and animals
 The first organisms were
microscopic bacteria,
which lived during this era
Paleozoic Era
 544 million – 245 million
years ago
 Era begins with one
supercontinent breaking
up into multiple
continents
 Fish, clams, snails, and
shellfish developed
 Early plants and forests
grew
Mesozoic Era
 Also called “Middle Life”
 245 million – 65 million
years ago
 Climate warmed,
allowing new plants to
grow (bananas, palms)
 Dinosaurs
Mesozoic Era Continued
 Continental plates
collided, creating the
Rocky Mountains
 This era produced veins
of gold, silver, copper,
lead, zinc, etc.
 Also produced gems
such as Yogo Sapphires
Cenozoic Era
Also called “recent
life”
65 million years ago –
present
Era introduces the first
mammals and
human beings
Cenozoic Era Continued
 First, Earth became dry and
desert-like, then Earth
became cool, wet and
snowy…creating the Ice Age
 After the last Ice Age,
megafauna either adapted or
became extinct.
 New climate helped new
mammals and plants develop