Lesson 5 Changes in Geology over Time - Delaware Valley ... · Overtime the sap hardens and ......

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Lesson 5 Changes in Geology over Time

Transcript of Lesson 5 Changes in Geology over Time - Delaware Valley ... · Overtime the sap hardens and ......

Lesson 5

Changes in Geology over Time

Distinguish between relative age and absolute age.

Discuss the future of Earth’s life and geologic structures.

Earth’s geologic history is determined by studying the relative and absolute ages of rock and fossils.

relative age – a rock layer’s age compared to other rock layers

fossil – any trace, imprint, or remains of a living thing preserved in earth’s crust

half-life – the time it takes for half the mass of a radioactive element to decay into other elements

absolute age - is a rock layer’s age in years

era – long stretches of time used to measure Earth’s geological history

period – one of the primary divisions of a geologic era

Original horizontality is the idea that sedimentary rocks form in horizontal layers.

Superposition is the idea that in a series of rock layers, the bottom layer is the oldest and the top layer is the youngest.

The two ideas together explain the rocks age.

Relative age is the age compared to other rock layers.

By looking at rock layers in an exposed hill or canyon wall,

Scientist can tell which layers are older than others.

Scientists use relative age to tell which layers are older than others.

By comparing rock layers across a large region, scientists can make a geologic column.

A listing of Earth’s rock layers from oldest to youngest.

Earth’s plates move and volcanoes erupt.

Layers of rock are pushed up or pulled down.

These changes are what makes relative ages of rock so interesting.

Conglomerate is rock composed of gravel, pebbles, and stone.

The following are events and circumstances that lead to rock layers and their changes (diagram page 299):

1. horizontal layers of rock forming,

2. layers tilting upward,

3. tops eroding,

4. or they are buried under more layers.

Infer

Cross sections of rock layers on each side of a large highway are the same.

What can you infer?

The rocks probably have the same relative age.

Critical Thinking

What processes might put younger rock beneath older rock?

Magma can rise up and harden into new igneous rock under older rock layers or seismic activity can cause areas of rock to turn and shift.

Fossils are the remains, traces, or imprints of living things preserved in Earth’s crust.

Rock layers often contain fossils.

Fossil Formation (diagram page 300)

1. A fish or another organism dies.

2. Then sediment buries the remains.

3. Impressions as well as hard body parts such as shells, teeth, or bone can be preserved as fossil.

4. Finally uplift and erosion can change the location of the fossil.

Fossils can form in many ways.

One way is if an insect gets trapped by flowing sap.

Overtime the sap hardens and becomes amber.

Fossils of foot prints are made when an animal walks on sand or wet soil.

If the footprint or fossil dries quickly then the fossil is preserved.

Plants can do the same thing.

If a plant gets stuck in mud or sand then they can leave an imprint of a fossil.

Because fossils are found in rock layers, we can determine their relative ages based on the layers in which they are found.

Index fossils are remains of living things that were wide spread but lived during a relatively short part of Earth’s history.

Fossils give clues on how Earth may have looked like in the past.

In the coal deposits of Pennsylvania and West Virginia there are fossils of fern plants.

These ferns grow in moist and warm weather.

This helps us to infer that West Virginia and Pennsylvania were both somewhat tropical a long time ago.

Infer

Explain how scientists can determine the kind of climate a place had long ago.

They can examine the fossil record to determine the kinds of plants and animals that lived at the time.

Critical Thinking

How can fossils give us clues about ancient environments?

Fossils can give us information about water levels and temperature changes by showing us what kinds of plants and animals were present in the area.

Each radioactive element has its own half-life.

Scientists can learn how long the process has been going on by comparing the original element with the decayed product.

Through this process they can figure out the absolute age of the rock.

The radioactive element uranium 235, or U-235 has a half-life of 700 million years.

You find out that the ratio of original element to decay product is 1:4.

That means 25% of the original is left.

One fourth is half of one half so it’s been two half-lives since the rock was created.

The age of the rock is 2 x 700 million years.

Scientist use fossil clues, the ages of rock layers, and evidence of crustal motion to tell the story of Earth’s geologic history.

Each era is described by the kinds of life that were dominant in that era.

They are split into periods.

Periods often are associated with major changes in Earth’s crust.

By looking at a geologic time scale you can compare eras and periods.

You can also see major events and life-forms on Earth using this scale.

Our knowledge of the dating of eras are all based off of fossils we find.

EON ERA PERIOD

P.

H

A

N

E

R

O

Z

O

I

C

540 mya

through today

CENOZOIC

Quarternary 1.8 mya-today

First humans, mammoths, mastodons, saber-toothed cats.

Neogene 24-1.8 mya

Australopithecus appears. First sheep, cattle, modern whales, bears, mice, rats, apes,

monkeys, dogs, modern birds appear.

Paleogene 65-24 mya

First deer, cats, pigs, tapirs, and rhinos, elephants, horses, owls, shrews, hedgehogs, and

rabbits evolve.

MESOZOIC

Cretaceous 146 to 65 mya

First flowering plants, snakes, crocodilians. K-T mass extinction at end kills dinosaurs, and

others

Jurassic 208 to 146 mya

Abundant dinosaurs, first birds.

Triassic 245 to 208 mya

First mammals, dinosaurs, frogs, turtles, crocodyloformes.

PALEOZOIC

Permian 280 to 245 mya

Sail-back reptiles. Amphibians abundant. Pangaea forms. Ends with mass extinction.

Carboniferous 360 to 280 mya

Widespread coal swamps. First reptiles, winged insects.

Devonian 408 to 360 mya

First amphibians, sharks, bony fish, ammonoids, and spiders. Many fish.

Silurian 438 to 408 mya

First insects, vascular plants on land.

Ordovician 505 to 438 mya

First land plants, corals, Nautiloids. Ends in mass extinction.

Cambrian 540 to 500 mya

Explosion of life forms. First shellfish, primitive fish, trilobites, corals, mollusks.

PROTERO-

ZOIC

2.5 billion

years ago to

540 mya

- Vendian 600 to 540 mya

Sponges, multi-celled animals appear. Supercontinent Rodinia.

- Early Proterozoic 2.5 billion years to 600 mya

Oxygen build-up on Earth. First multi-cellular life.

Infer

Trilobites disappeared from the fossil record 450 million years ago.

What can you infer from this information?

Something must have happened 450 million years ago that caused trilobites to become extinct, such as a change in climate or ocean temperatures.

Critical Thinking

What evidence is there that ice ages come and go?

The moraines of ancient ice ages support their existence. Furthermore, geologic columns and ice columns indicate past changes in weather patterns and climate, and these changes support the idea of recurring ice ages.

Earth is always changing.

An island called Surtsey near Iceland formed in 1963 by volcanic eruptions.

A new Hawaiian island is slowly building up.

In 1883 the volcano Krakatau on the island of Indonesia erupted destroying most of the island.

Today a volcano called Anak Krakatau is forming in this area.

The life on Earth's crust is changing, just like Earth’s surface.

New organisms appear and some become extinct because they couldn't adapt to new conditions.

Some became extinct due to human behaviors.

At times certain animals are thought to be extinct.

In 2005 scientist saw a wood pecker in Arkansas which they believed to be extinct but they weren't.

New species are being discovered every year.

In 1977 scientists studying the sea discovered a previously unknown kind of life: tube worms, which live on the ocean floor near hot geothermal vents.

Later, they discovered organisms living off the minerals emitted by these vents.

In the 1990's another new kind of life was discovered living near the mouths of lobsters.

Infer

What effect might environmental changes have on organisms?

Organisms might not be able to find food or other resources, or they might not be suited for changes in climate.

Critical Thinking

How could global warming change Earth’s surface?

Melting ice from changing climates could raise sea levels and flooding of low lying areas could occur.