ERAS OF THE GEOLOGIC TIME SCALE

SCIENTISTS HAVE DIVIDED THE EARTH’S HISTORY INTO 4 MAJOR PARTS:

THE GEOLOGIC TIME SCALE

Scientists have divided geologic history into 4 main parts:

Precambrian TimePaleozoic EraMesozoic EraCenozoic Era

Precambrian Time

4.6 billion – 543 million years ago Life began during this time Atmosphere made of water vapor, CO2 & N2

Volcanic eruptions, meteorites, violent storms & intense solar radiation

Origin of Life?

• Extraterrestrial• Life came from outside the planet(i.e. meteor)

• Creation• Divine forces created life

• Non-Living Matter• Spontaneous assembly of molecules

4 billion years ago - Earth began to cool

Water condensed and fell as rain

Atmosphere of early Earth Hydrogen (H2) Volcanic gas

(i.e. methane (CH4), ammonia (NH3), CO, SO2, N2, CO2)

No free oxygen or ozone

Energy stimulated chemical reactions

=ProteinsNucleic AcidsLipidsCarbohydrates

UV

+

How Did Life Begin?

In the oceans Energy from radiation

and storms caused simple chemicals in the oceans & atmosphere to react

More complex molecules were made Molecules joined to form cells Prokaryotes: single-celled organisms

(without a nucleus) that did not need O2 to survive

Photosynthesis & Oxygen Cyanobacteria (type of prokaryotic

organism) appears over 3 bya Uses sunlight to produce food

Photosynthesis & Oxygen Oxygen gas is released into oceans & air Oxygen molecules react to form Ozone,

which absorbs harmful radiation form the sun

Now possible for life to exist on Earth’s surface

Photosynthesis & Oxygen

VOCs Volatile organic compounds

NOx Nitrogen-oxygen compounds

Multicellular Organisms

Eukaryotes appear in the fossil record Organism that contain a nucleus Will evolve into organisms composed of many

cells

Paleozoic Era (543 – 248 mya)

“Old life” or “Ancient life” Large fossil record

Sponges, coral, squid, clams, trilobites, fish, sharks

Reptiles, amphibians, fish, worms, & ferns first appear

Paleozoic Era – Life on Land

Plants, fungi, & air-breathing animals slowly colonized land Crawling insects first animals to live on land Reptiles & winged insects appear near the end

of era LARGEST Mass extinction marks end of

era 90% of species extinct Oceans completely changed

Mesozoic Era (248 – 65 mya)

“Middle Life” or “Age of Reptiles” Dinosaurs dominate Earth for 150 million

yrs First birds appear Conifers appear Flowering plants appear late in era

End of Mesozoic Era

Mass Extinction Dinosaurs Many other plant & animal species Meteorite hit Earth

Dust, smoke, fires Temperatures dropped

for many years

Cenozoic Era (65 mya – today)

“Recent Life” or “Age of Mammals” Many mammals, birds, insects &

flowering plants Saber-toothed cats,

camels, small horses

Cenozoic Era Today

Era we are currently living in Climate changed many times during era

Periods of ice ages Animals migrate, adapt, or become extinct