Transcript History of the Earth

History of the Earth
Chapter 12
How Old is the Earth?
Early Earth
4.5 Billion Years Old
Before then it was a fiery ball of molten rock.
The water vapor from the atmosphere cooled
and formed vast oceans.
How Old is the Earth?
How do we know?
Evidence of the earth’s age can be found in
rock.
Radiometric Dating
The estimation of age of an object by measuring
its content of radioactive isotopes.
Radioactive Decay
Radioactive Decay
Radioactive isotopes are unstable isotopes that
break down giving off energy in the form of
radiation.
The Evidence of Evolution
•
Fossils
–
–
Preserved or
mineralized remains
or imprint of
organism that lived
long ago
Show a pattern of
development form
early ancestors to
now
Evidence of Evolution
• Most scientists agree that:
1.Earth is about 4.5 billion years old
2.Organisms have inhabited Earth for most of its history
3.All organisms living today share common ancestry with
earlier, simpler life-forms.
Evolution of Cellular Life
• Precambrian Era
– The first bacteria have been found to have lived 2.5
billion years ago during this era
– Cyanobacteria
•
•
•
•
First prokaryotes
First organisms to live on earth
Photosynthetic bacteria
Released oxygen into the atmosphere
– Protists
• First Eukaryotes
• Large group of unicellular and multicellular organisms
Evolution of Cellular Life
• Cambrian Period
– About 1 billion years
ago
– The first animals
probably originated
from this period
– This great
diversification of
animals is called the
“Cambrian Explosion”
Evolution of Cellular Life
• Ordovician Period
– About 505 to 438 million years ago
– This is the time when animal diversity
abounds and the first jawless fishes swam the
seas
– The appearance of more sea animals occurs
during this period
• Mass Extinction
– During this period a large percentage life on
earth went extinct
Evolution of Cellular Life
• Silurian Period (437 million years ago)
– During this period Plants, arthropods, and fungi invade
the land
• May have been the first multicellular organisms to actually live
on land.
• Jawed fishes appear in the seas
• Devonian Period (405 million years ago)
– During this period bony fishes become abundant
– Amphibians
• The first vertebrates to leave the sea
– Second Mass Extinction
Evolution of Cellular Life
• Carboniferous Period (360 million years ago)
– Reptiles who evolved from amphibians have
begun to inhabit the earth
• Permian Period (290 million years ago)
– Third Mass Extinction
• Triassic Period (250 million years ago)
– The first dinosaurs and Mammals appear
– Fourth Mass Extinction
Evolution of Cellular Life
• Jurassic Period (210
million years ago)
• Cretaceous Period
(150 million years
ago)
– This period is marked
by the appearance of
flowering plants
– Fifth mass extinction
Evolution of Life
• Tertiary Period (65
million years ago)
– Due to the continents
drifting birds and
Mammals spread
– Major mammal groups
evolve and become
abundant on land
– Appearance of
Australopithecus
Evolution of Cellular Life
• Quarternary Period (5
million years ago–today)
– During this period the
first Homo sapiens
walked the land and
continue to this day.