Earth's history

Geology

DEFINITION

GEOLOGYGreek Earth

Geology = The study of Earth

The study of

The Earth’s Four Spheres

The Geospher eThe solid earth, consisting of

the entire planet from the center of the core to the outer crust.

Geosphere

INNER CORE- HOT!!!! –

Thought to be as hot as the surface of the Sun!

- Solid

- Composed of Iron and Nickel

OUTER CORE• HOT!

(but not as hot as the inner core)

• Liquid

• Composed of Iron and Nickel

MANTLE• Still hot! – but

not as hot as the core!

• Largest layer

• Composed of various materials

• Solid and liquid

CRUST• Cool

• Where we live on

• Composed of rocks, various materials make up the crust

• Solid or Liquid?

Even though 70% of the Earth’s surface is water, there is crust under the water. The water sits on top of the crust!

LithosphereThe cool, rigid outer part of Earth, about 100

kilometers thick, which includes the crust and the upper most mantle.

According to the theory develop in 1960s, the lithosphere is broken down into seven major segments called TECTONIC PLATES. These tectonic plates float on the weak, plastic, mantle rock , called ASTHENOSPHERE beneath, and glide across earth.

-The Earth’s crust moves!!!!!-The continents have not always been arranged like they are today.

- The Earth’s crust is divided into segments called plates.

Pangaea• Supercontinent that existed 250 million

years ago• All the land made up 1 continent until its

split into the modern day configuration of the continents.

• Discovered by Alfred Wegner in 1912, but not accepted by the public until after his death in the 1950’s.

The HydrosphereIncludes all of earth’s water, which

circulates among oceans, continents, glaciers and the atmosphere.

Earth’s Water Percentage

Oceans 97.5 %

Glaciers 1.8 %

Groundwater 0.63 %

Streams and lakes 0.01 %

Atmosphere 0.001 %

OCEANS cover 71 % of earth and contain 97.5 % of its water.Ocean currents transport heat across vast distances, altering global climate.

GLACIERS cover 10 % earth’s land surface and about 1.8 % of earth’s water.

Only 0.64 % of Earth’s total water exists on the continents as liquid. Although it is a small proportion FRESHWATER is essential to life on earth.Lakes , rivers, water and streams are the most visible reservoirs of continental water but they constitute only 0.01 % of earth’s water.

GROUNDWATER which saturates rock and soil of the upper few kilometers of the geosphere is much more abundant and accounts for 0.63 % of Earth’s water.

Water located in the gaps and pores in rocks below earth’s surface.

Water gets there because the soil in places is permeable which means water can easily pass through.

It can collect in large underground lakes called aquifers.

Wells can be dug to access groundwater.

Only a miniscule amount, 0.001 % , EXISTS IN THE ATMOSPHERE, but because this water is so mobile , it profoundly affects both weather and climate of the planet.

The total amount of water on the Earth remains fairly constant.

The water moves above, across, and through Earth’s crust and ecosystems.

The Water Cycle

The Sun

• Heat energy from the sun drives the water cycle.

• Heat reaches the Earth by radiation.

Evaporation

• The process of liquid water changing into water vapor.

• Oceans contribute about 80% of all the water vapor in the air.

Transpiration

• The process by which plants release water vapor into the air through their leaves

Condensation

• The process in which water vapor changes into liquid water as the water vapor rises into the air and cools.

• When water vapor condenses on particles in the air and tiny water droplets or ice crystals form, a cloud is visible.

Precipitation

• Solid or liquid water that falls from the air to Earth• Rain, snow, sleet, and hail are forms of

precipitation.• Form when drops of condensation in clouds come

together and grow too large to remain suspended• Precipitation always “runs” downward due to

gravity

All precipitation starts as snow!

• Snow falls into warm air and melts = rain• Snow falls into cold air and never melts on

the way down=snow • Snow falls, melts, and refreezes as it travels

through cold air=sleet• Snow falls, melts, refreezes and becomes

the “seed” kept suspended by updrafts until it gets too heavy and falls=hail

Where does precipitation go?

• Most falls back into the ocean

• Some falls on the ground and soaks in

• Some falls on the ground and runs off the surface into tributaries (streams and small rivers that feed into a main river)

The Atmosphere

Mixture of gases, mostly nitrogen and oxygen, with smaller amounts of Argon, CO2 and other gases.

Held to earth by gravity and thins rapidly with altitude.Ninety nine percent is concentrated in the first 30 kilometers , but a few traces remain as far as 10,000 km above earth’s surface.

The BiosphereThe zone of earth comprising all

forms of life in the sea , on land and in the air.

Geologic Time:A story in the rocks

IT IS ESTIMATED THAT THE EARTH FORMED ALONG WITH THE SOLAR SYSTEM 4.6 BILLION YEARS AGO (4,600 MYA)

GEOLOGIC TIME SCALE

A SUMMARY OF THE MAJOR EVENTS IN EARTH’S HISTORY

EON – largest segment of geologic time

ERA

PERIOD

EPOCH – smallest segment of geologic time

RELATIVE TIME VS. ABSOLUTE TIME

PLACES EVENTS IN A SEQUENCE BUT DOES NOT IDENTIFY THEIR ACTUAL DATE OF OCCURRENCE

IDENTIFIES THE ACTUAL DATES OF GEOLOGIC EVENTS

EXAMPLE

A LIST IN CHRONOLOGICAL ORDER OF WHAT YOU HAVE DONE TODAY UP UNTIL THIS TIME

THE EXACT TIMES AT WHICH YOU DID THESE THINGS

Principle of Original Principle of Original HorizontalityHorizontality

• The principle of original horizontalityprinciple of original horizontality states that sediments are deposited in horizontal layers that are parallel to the surface on which they were deposited.

• This implies that tilted or folded layers indicate that the crust has been deformed.

LAW OF SUPERPOSITION- IN UNDISTURBED SEDIMENTARY ROCKS THE OLDEST ROCK LAYERS ARE AT THE BOTTOM AND THE YOUNGEST ARE AT THE TOP.

LAW OF CROSS-CUTTING RELATIONSHIPS-

The obvious principle that a rock or feature must first exist before anything can happen to it.

Igneous Intrusions and ExtrusionsIgneous Intrusions and Extrusions

When magma forces its way into cracks or crevices in crustal rock and solidifies, it forms a mass of igneous rock called an intrusionintrusion.

When lava solidifies at the surface it forms a mass of igneous rock called an extrusionextrusion.

Since the rock thatrock that the magma moved through, or over, existed existed priorprior to the intrusion, (or extrusion), it must be oldermust be older.

Evolution

The biological theory that life forms have changed in their physical and genetic characteristics overtime.

The Principle of Faunal Succession

States that species succeeded one another through time in a definite and recognizable order and that the relative ages of sedimentary rocks can therefore be recognized from their fossils.

UnconformityAn interruption in sediment deposits or

a break between eroded igneous and overlying sedimentary layers, causing a gap in the geological record for that place.

UNCONFORMITY- A PLACE IN THE ROCK RECORD WHERE LAYERS OF ROCK ARE MISSING BECAUSE OF UPLIFT AND EROSION. THE RESULT CAN BE A LARGE AGE DIFFERENCE BETWEEN THE ROCKS ABOVE AND THOSE BELOW THE EROSIONAL SURFACE (IT APPEARS LIKE A SQUIGGLY LINE IN A CROSS-SECTION)

MATCHING OF ROCK LAYERS THAT CAN BE SEEN AT THE EARTH’S SURFACE, OVER A LARGE AREA

A KEY BED IS A THIN, WIDESPREAD LAYER, USUALLY OF VOLCANIC ASH, THAT CAN BE USED TO CORRELATE AN EXACT POINT OF TIME

• BedrockBedrock is the solid, unbroken rock of the crust.

• An outcropoutcrop is bedrock that is exposed at the Earth’s surface.

– OutcropsOutcrops provide opportunity for geologists to directly study the layers of the bedrock, tracing them from one location to another – called “walking an “walking an outcrop”.outcrop”.

A FOSSIL IS ANY EVIDENCE OF EARLIER LIFE PRESERVED IN THE ROCK

ORIGINAL REMAINS (RARE) – THE ACTUAL UNCHANGED REMAINS OF THE PLANT OR ANIMAL ARE PRESERVED.

REPLACED REMAINS – THE SOFT PARTS OF THE ORIGINAL ANIMAL HAVE DISAPPEARED AND THE HARD PARTS HAVE BEEN REPLACED BY MINERAL MATERIAL. (PETRIFIED WOOD)

TRACE FOSSILS – EVIDENCE OF LIFE OTHER THEN REMAINS, WHICH INCLUDES ANY IMPRESSIONS LEFT IN THE ROCK. (TRAILS, FOOTPRINTS, TRACKS, BURROWS)

MOLDS AND CASTS – FOSSIL SHELLS OR BONES ARE DISSOLVED COMPLETELY OUT OF THE ROCK LEAVING A HOLLOW DEPRESSION IN THE ROCK. NEW MINERAL MATERIAL FILLS THE MOLD IT FORMS A CAST OF THE ORIGINAL FOSSIL.

• Index fossilsIndex fossils are fossils or organisms that lived over an extensive area, preferably over the entire Earth, for relatively short periods of time.

• Index fossilsIndex fossils are useful in correlating the sedimentary rocks in which they are found.

INDEX FOSSIL

INDEX FOSSILS

Fossil CorrelationFossil Correlation

Volcanic Time MarkersVolcanic Time Markers

• Severe volcanic eruptions can deposit a thin layer of volcanic ashvolcanic ash over the surface of the entire Earth.

• These layers within a rock sequence may remain distinguishable and provide a time provide a time markermarker. (Similar to index fossils)

MEASURING ABSOLUTE TIME

EACH RING REPRESENTS A SINGLE YEAR (SPRING/FALL) THE WIDTH OF THE RING DEPENDS UPON THE TEMPERATURE AND RAINFALL

TREE RINGS

GLACIAL LAKE DEPOSITS. A THICK LIGHT COLORED LAYER IN THE SUMMER AND A THIN DARK LAYER IN THE WINTER

VARVES

RADIOACTIVE DATING

RADIOACTIVE ISOTOPES ARE ATOMS OF ELEMENTS THAT GIVE OFF RADIATION FROM THEIR NUCLEI

RADIOACTIVE DECAY IS THE PROCESS BY WHICH A RADIOACTIVE ISOTOPE CHANGES INTO A NEW STABLE ELEMENT

USED TO DATE FAR BACK IN TIME. CERTAIN ROCKS CONTAIN RADIOACTIVE ISOTOPES

THE RATE AT WHICH A RADIOACTIVE ELEMENT DECAYS. IT IS THE TIME IT TAKES FOR HALF OF THE ATOMS OF THE RADIOACTIVE ELEMENT TO DECAY TO A STABLE END PRODUCT (SEE PAGE 1 OF THE ESRT)

AT THE END OF EACH HALF-LIFE, HALF OF THE RADIOACTIVE MATERIAL REMAINS

DAUGHTER ISOTOPE = THE STABLE ISOTOPE THAT HAS BEEN CHANGED

PARENT ISOTOPE = THE RADIOACTIVE ISOTOPE THAT BEGINS

RADIOCARBON DATING USES THE RADIOACTIVE ISOTOPE CARBON-14 FOUND IN ALL LIVING THINGS. BECAUSE CARBON-14 IS CONTINUALLY ABSORBED BY FOOD AND WATER IT STAYS CONSTANT IN LIVING THINGS.

WHEN THE LIVING THING DIES THE PERCENTAGE OF CARBON-14 DECREASES AT THE RATE OF ITS HALF-LIFE. CAN BE USED TO DATE BACK ABOUT 100,000 YEARS

URANIUM LEAD METHOD IS USEFUL TO DATE ROCKS OLDER THAN 10 MILLION YEARS. CAN BE USED ONLY ON IGNEOUS ROCKS THAT CONTAIN THE RIGHT KIND OF URANIUM

RUBIDIUM-STRONTIUM METHOD CAN ALSO BE USED TO DATE OLDER ROCKS BECAUSE OF ITS LONG HALF-LIFE. IT IS ALSO VERY COMMONLY FOUND IN IGNEOUS ROCKS.

POTASSIUM-ARGON METHOD IS VERY USEFUL SINCE POTASSIUM-40 CAN BE FOUND IN METAMORPHIC, SEDIMENTARY, AND IGNEOUS ROCKS. IT CAN DATE OLDER ROCKS BUT MAY ALSO DATE ROCKS AS YOUNG AS 50,000 YEARS

Geologic Time ScaleGeologic Time Scale• Geologic time is subdivided divided into units

based on fossil evidence.• There are 4 major divisions:

– PrecambrianPrecambrian – represents the first 85% of Earth’s history (mostly devoid of fossils).

– Paleozoic EraPaleozoic Era – represents ~ 8.5% of Earth’s history (invertebrates, fishes, amphibians, vertebrates and land plants first appear).

– Mesozoic EraMesozoic Era – rep. ~ 3.5% of Earth’s history (dinosaurs, earliest birds, and mammals).

– Cenozoic EraCenozoic Era – rep. ~ 1.4% of Earth’s history (humanoids show up late ~0.04% of history).

What is the Earth’s time scale?

• The Geological time scale is a record of the life forms and geological events in Earth’s history.

• Scientists developed the time scale by studying rock layers and fossils world wide.

• Radioactive dating helped determine the absolute divisions in the time scale.

Divisions of Geologic Time• Eras are subdivided into periods...periods are

subdivided into epochs.Era

Period

Epoch

E + P = EP

Divisions of Geologic Time

• Geological time begins with Precambrian Time. Precambrian time covers approximately 88% of Earth’s history.

FOUR Eras…

• PRE-CAMBRIAN – 88% of earth’s history

• Paleozoic (ancient life)– 544 million years ago…lasted 300 million yrs

• Mesozoic (middle life)– 245 million years ago…lasted 180 million yrs

• Cenozoic (recent life)– 65 million years ago…continues through present day

Today…

• Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic Era.

Which unit is the largest?

Which unit is the smallest?

Paleozoic Era (Ancient Life)• The Cambrian period is the 1st period of the Paleozoic Era.

“Age of the Trilobites”• Explosion of life in the oceans began during this era. • Most of the continents were covered in warm, shallow seas.

– Invertebrates were dominate - Trilobites– Fish emerged during this time– Fish led to the arrival of amphibians

• The end of the Paleozoic era is called the “Age of Amphibians”

– Early land plants including mosses, ferns and cone-bearing plants.– The early coal forming forests were also formed during this time.

Paleozoic Era• Much of the limestone quarried for building and

industrial purposes, as well as the coal deposits of western Europe and the eastern United States, were formed during the Paleozoic.

• The Cambrian (beginning) opened with the breakup of the world-continent Rodinia and closed with the formation of Pangaea, as the Earth's continents came together once again. – This event is thought to have caused the climate

changes that led to mass extinction event.• The Appalachian mountains were formed during this

time.

Paleozoic Era

• At the end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species and 70% of land animals.– Possible causes of this Mass Extinction Event

• Lowering of sea levels when the continents were rejoined as Pangaea (convergent boundary)

• Increased volcanic activity (ash and dust)• Climate changes – cooler climate

Trilobites

• Lived in Earth’s ancient seas• Extinct before the dinosaurs came

into existence• Cambrian Period is know as the

“Age of the Trilobites”

Brachiopods

• Marine animals that resemble clams.

Early Fish

Early fish did not have jaws.

Some species of sharks were in existence at this time.

Frilled Shark that was found in Japan in January 2007. This shark was considered a “living fossil”

Early Land Plants

Cone bearing plants

Ferns

Mosses

Mesozoic Era – Middle Life• At the beginning of this era the continents

were joined as Pangaea. • Pangaea broke up around the middle of this

era.• Reptiles became the most abundant animals

because of their ability to adapt to the drier climate of the Mesozoic Era.– Skin maintains body fluids– Embryos live in shells

Mesozoic Era

• Dinosaurs were also very active in this era.– First small dinosaurs appeared in the Triassic

Period.– Larger and more abundant dinosaurs appeared in

the Jurassic Period.

• Small mammals and birds also appeared during this era.– The mammals were small, warm-blooded animals.

Hair covering their bodies.• These characteristics help them survive in changing

environments.

Mesozoic Era• The main plant life of this time were

Gymnosperms or plants that produce seeds, but no flowers. – Pine Trees

• Flowering plants appeared during the END of this era.

Mesozoic Era• This era ended with a mass extinction event about

65 million years ago.– Many groups of animals, including the dinosaurs

disappeared suddenly at this time.

• Many scientists believe that this event was caused by a comet or asteroid colliding with the Earth.

Mesozoic Era – Mass Extinction Event

• Asteroid or Comet collides with Earth.

– Huge cloud of smoke and dust fills the air– Blocks out sunlight– Plants die– Animals that eat plants die– Animals that eat plant-eaters die.

• However, not all forms of life died during this event. Many animals that you see today are descendants from the survivors of this extinction event.

Dinosaurs

Mesozoic Reptiles

Mesozoic Mammals

Mesozoic Plants

Flowering plants evolved towards the end of the Mesozoic Era.

Cenozoic Era – Recent Life• Began about 65 million years ago and continues today!!!!!

– Climate was warm and mild.– Marine animals such as whales and dolphins evolved.

• Mammals began to increase and evolve adaptations that allowed them to live in many different environments – land, air and the sea.– Grasses increased and provided a food source for grazing animals

• Many mountain ranges formed during the Cenozoic Era– Alps in Europe and Himalayas in India; Rocky Mountains in the

USA

Cenozoic Era• Growth of these mountains may have helped to cool

down the climate– Ice Ages occurred late in the Cenozoic Era (Quaternary

Period).

• As the climate changed, the animals had to adapt to the rise and fall of the oceans caused by melting glaciers.

• This era is sometimes called the “Age of Mammals”

Cenozoic Era• Marine animal examples:

– Algae, Mollusks, Fish and Mammals

• Land animal examples:– Bats, Cats, Dogs, Cattle and Humans– Humans are thought to have appeared around 3.5 million

years ago (during the most recent period – Quaternary).

• Flowering plants were now the most common plant life.

Cenozoic Mammals

Flowering Plants were common during the Cenozoic Era