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.

History of the EarthHistory of the Earth

Chapter 12Chapter 12

How Old is the Earth?How Old is the Earth?

Early Earth4.5 Billion Years OldBefore 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 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 DecayRadioactive Decay

Radioactive DecayRadioactive isotopes are unstable isotopes that

break down giving off energy in the form of radiation.

The Evidence of EvolutionThe 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 EvolutionEvidence 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 LifeEvolution 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 LifeEvolution 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 LifeEvolution 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 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 LifeEvolution 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 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 LifeEvolution 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 LifeEvolution 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.