Geologic Time Chapter 21.1, 22, 23, 24

Organization of Ch 21-24 Ch 21.1 – Describes the geologic time scale Ch 22 – Precambrian Earth Section 1: Early Earth Section 2: Formation of the Crust and Continents Section 3: Formation of the Atmosphere and Oceans Section 4: Early Life on Earth Ch 23 – Paleozoic Era Ch 24 – Mesozoic and Cenozoic Eras

Ch 21.1 Section Assessment Questions, pg 556: 1-7 How did geologists determine the divisions of the geologic time scale? What does the geologic time scale indicate about the change in life-forms over time? What do the names of the three eras of the Phanerozoic mean? What major change occurred in life-forms at the end of the Proterozoic? How were the geologic time periods named? On what basis are they defined? Why is the use of living faunas acceptable for defining the periods and epochs of the Cenozoic Era? Make bar graph showing breakdown of the scale. Fossil record Wide variety of life-forms, most have become extinct Paleo – ancient, zoic – life, Meso – middle, Cenos – recent Hard parts (skeletons, shells) Location where rocks were first studied, distinctive groups that lived nearby, or a geographic feature , defined by the last fossil occurrence of a particular group of organisms Many plans that originated during the Cenozoic era still exist today. Their fossils can be used to define the epochs of the Cenozoic. Precambrian – 90%, Paleozoic – 6%, Mesozoic – 4%, Cenozoic – 1%

Why do we care? By studying the characteristics of rocks and fossils within them, geologists can interpret The environment the rocks were deposited in Reconstruct Earth’s history Possibly predict events or conditions of the future

Geologic Time Scale Defn: record of Earth’s history from its origin to the present used by scientists around the world to correlate: Geologic events Environmental changes Development of life-forms that are preserved in rocks Names of periods don’t change, but the years marking the beg. and end are continually being refined.

Geologic Time Divisions Eon – longest unit, measured in billions Era – next-longest, hundreds of millions to billions “Paleozoic” = old life “Mesozoic” = middle life “Cenozoic” = recent life Period – 10’s to 100’s of millions of years Epoch – smaller divisions, millions to 10’s of millions

Eons Longest unit Measured in billions Three Eons Archean Eon (part 1 Precambrian Time) NO LIFE Proterozoic Eon (part 2 Precambrian Time) SINGLE-CELLED LIFE Phanerozoic Eon (3 Eras) MULTICELLULAR LIFE

Eras Next-longest Hundreds of millions to billions Defined by differences in life-forms found in rock Three Eras “Paleozoic” = old life “Mesozoic” = middle life “Cenozoic” = recent life

Periods Second shortest 10’s to 100’s of millions of years Defined by life-forms that were abundant or became extinct during the time the rocks were deposited

Epochs Smaller divisions Millions to 10’s of millions ONLY IN CENOZOIC…WHY?

Precambrian Time (Early Earth) Makes up the first 90% of geologic time Age of Earth Land Atmosphere Oceans Life

How old is Earth? 4.6 billion years old Evidence? Rock age – 3.96 by (radiometric dating) Zircon minerals – 4.1-2 by (radiometric dating) Meteorites – 4.5-7 by (radiometric dating) Moon rocks – 4.6 by (radiometric dating)

Land How did land form? Earth cooled and crust formed Early crust used to be mainly basalt. Densities of different materials sorted out the layers of earth (differentiation) Melting of basaltic crust and then recrystallization formed granitic crust. Why is the iron and nickel outer core liquid but inner core solid? More pressure in inner core increases its melting point. Less pressure in outer core. Early Earth  molten rock Present  continents

Atmosphere Early Earth  Present Earth  Carbon dioxide (CO2), N2, Methane (CH4), Water vapor (H2O), Carbon monoxide (CO), Ammonia (NH3) HOT TEMPS Present Earth  N2 (71%), O2 (21%), Ar (0.9%), CO2 How?! Stromatolites! Evidence?! Red beds! Avg global temp is 25 degrees Celsius

Oceans Early Earth  NO OCEANS Present Earth  71% OCEANS! HOW?! Meteorites and comets brought water Volcanoes released during Archaean Eon (outgassing) LOTS OF RAIN

Resources Climate Resource  http://www.scotese.com/climate.htm Landmass Resource  http://www.scotese.com/earth.htm

ERAS Landforms Flora (plants) Fauna (animals) Extinctions Climate

Paleozoic Era - Landforms - First supercontinent “Rodinia” had just broken apart - Plate tectonics, mountain building

Paleozoic Era - Flora - Rainforests covered the earth - Vascular plants appeared (allowed for taller, stronger plants) - Ferns

Paleozoic Era - Fauna - Reptiles appear - Amphibians - Fishes w/backbones (vert) - Trilobites (org w/hard parts) - Marine life!! - (Stromatolites in Precambrian)

Paleozoic Era - Extinctions - End of Paleozoic Era was the Permian Extinction (more than 90% of species died) - 1st mass extinction ended the Ordovican period (marine life)

Paleozoic Era - Climate - Global cooling continued - Ranged from temperate to cold to steamy swamp

Mesozoic Era - Landforms - Breakup of “Pangaea” - Tectonic activity, mountain building - Sea levels rose

Mesozoic Era - Flora - Flowering plants first evolved

Mesozoic Era - Fauna - Birds evolve - Dinosaurs, Crocodiles, early mammals evolve, ocean/air reptiles evolve

Mesozoic Era - Extinctions - Cretaceous extinction ended Mesozoic era and rid dinosaurs

Mesozoic Era - Climate - Sandy, desert interior - Poles moist, temperate - Mild

Cenozoic Era - Landforms - Major tectonic activity, continents moved to their current positions

Cenozoic Era - Flora - Grasslands spread - Many more flowering plants

Cenozoic Era - Fauna - Hominids, humans, cats, whales, bats

Cenozoic Era - Extinctions - Due to changes in CO2, we could be entering the world’s next extinction? - Just like the extinction that killed the dinosaurs?

Cenozoic Era - Climate - Most recent ice age - Climate changed back and forth, warmer and cooler