Unit 2 Lesson 1: Geologic Change Over Time

Geologic Change Over Time

How do we learn about Earth's history?

Poll

True or False: Once rock forms it never changes.

• True

• False

Poll

True or False: Fossils can tell us which animals lived at a certain time.

• True

• False

Poll

True or False: The climate is exactly the same all over the world.

• True

• False

Poll

True or False: A volcano erupting is an example of a geologic process.

• True

• False

Open Ended

What can you infer about the environment in which this fossil probably formed?

The idea that erosion has occurred the same way throughout Earth's history is an example of uniformitarianism.

• What does this term mean?

Uniformitarianism

States that geologic processes that happened in the past can be explained by current geologic processes.

Open Ended

How do these two images show the principle of uniformitarianism?

How do organisms become preserved as fossils?

• FOSSILS are the trace (or remains) of an organism that lived long ago.

• Most commonly found in sedimentary rock.

• Fossils can be shells, skeletons, body parts, burrows, or ancient coral reefs.

Trapped in Amber

• Organisms get stuck in soft sticky tree sap that hardens and gets buried and preserved.

• Some of the best fossils are formed this way.

Trapped in Asphalt

• Asphalt ("tar") wells up to Earth's surface in certain spots.

• Organisms get caught in the thick, sticky goo.

Buried In Rock

• Most of the time organisms die and are quickly decomposed or eaten by other organisms.

• Getting buried slows decay, and the hard parts of the organism eventually become part of the rock.

• "Bone" is no longer present, but the minerals remain.

Frozen

• Freezing temperatures slow down decay, so organisms that get frozen may get preserved by the ice.

• Ötzi, also called the Iceman, is the natural mummy of a man who lived between 3400 and 3100 BCE, discovered in September 1991 in the Ötztal Alps (hence the nickname "Ötzi") on the border between Austria and Italy.

Petrification

• Happens when an organism's tissues are replaced by minerals.

Trace Fossils

• A fossilized structure that formed in sedimentary rock by animal activity.

• A "trace" or sign of the organism that it left behind, not the organism itself.

• Tracks, burrows, trails, or waste (called dung or coprolite).

Multiple Choice

What might a trace fossil tell you about an organism?

• What they did no. 2

• How they behaved

• What they ate

• How they moved

Multiple Select

Which methods seem to preserve fossils in a way that provide the best information about the organism?

• Amber

• Asphalt

• Buried in Rock

• Frozen

• Pertification

What can fossils tell us?

The FOSSIL RECORD contains all of the fossils found on Earth.

It shows PART of the history of life on Earth.

Open Ended

Why isn't the fossil record a complete history of all life on the planet?

Open Ended

What are two types of changes on Earth fossils can give information about?

Fossils also tell us about environmental changes over time.

• Fish fossils indicate there was once water where there is now dry land.

• Fossils of trees and dinosaurs have been found in Antarctica.

• Palm fronds indicate a tropical environment.

The Atacama desert is the driest place on Earth (currently).

Fossils can tell us how life forms have changed over time

• Changing conditions on Earth influence an organisms survival and the adaptations that are selected.

• The relationships between living organisms and fossils as well as between different fossils.

How does sedimentary rock show Earth's history?

• Rock and mineral fragments that are weathered move from one place to another by erosion.

• Eventually, sediment is deposited in LAYERS.

• New layers cover older layers, which become compacted.

• Dissolved minerals, such as calcite and quartz, separate from water that passes through the sediment, forming a natural cement.

• Deposition --> Compaction --> Cementation --> Sedimentary Rock

Multiple Select

Which process(es) can produce sediments?

• physical weathering

• chemical weathering

• death and decay of organisms

• cementation

• deposition

Multiple Choice

Which is the correct order of steps in forming sedimentary rock?

• compaction, deposition, cementation

• deposition, compaction, cementation

• cementation, deposition, compaction

• all of the above

Scientists use different characteristics to classify sedimentary rock...

• This provides evidence of the environment the rock formed in.

• Also tells us what it's made of.

Composition

• Shows the source of the sediment that makes up the rock.

• Sandstone = sand grains get cemented together.

• Limestone = remains of dead plants and animals

• Coal = partially decomposed plant material buried beneath sediment.

Texture

• Can show how the material was carried and deposited, providing clues about the environment at the time.

• Layers can differ from one another; kind of material, color, and size of sediments.

Special Features

• "Ripple Marks" record motion of wind or water waves over sediment.

• "Mud Cracks" form when fine-grained sediments covered by water are suddenly exposed to air and dry out quickly.

Studying sedimentary rocks on Mars

Multiple Choice

What kind of environment may have been present if ripple marks are found?

• a hot dry environment

• a shallow body of water

• a deep ocean

• fast moving water

Multiple Choice

Mud cracks in sedimentary rock have been found on Mars. This suggests that

• deep water may have remained on Mars for a very long time.

• Mars was affected by glacial activity.

• a lot of wind erosion has occurred on Mars.

• a shallow body of water may have dried very rapidly.

What do earth's surface features tell us?

• Earth's surface is ALWAYS changing.

• TECTONIC PLATES are divisions of the Earth's surface (the lithosphere).

• They move, causing the continents to change position over time.

Earth's Tectonic Plates

At one time, the continents formed a single land mass called PANGEA.

Pangea broke apart about 200 million years ago.

• Movement hasn't stopped.

Earth in 200 million years

Evidence of Pangea

• Distribution of rock types, mountains, and fossils.

• E.g. Appalachian and Atlas Mountains

Landforms Change Over Time

• When plates pull apart, magma can be released in volcanic eruptions.

• When plates collide, volcanoes and mountains can be created.

• When plates grind past one another, breaks in Earth's surface form, causing earthquakes.

Multiple Choice

What kind of movement may have occurred to form this landform?

• Plates are separating

• Plates are sliding past one another quickly

• Plates are colliding with one another

Weathering and erosion break down landforms.

• For example high, jagged mountains become more rounded over time.

• This can provide clues about the geologic history of the mountains.

Multiple Choice

Are these mountains most likely "old" or "young"?

• Old

• Young

What can other materials tell us about Earth's climate history?

• The CLIMATE of an area describes the weather conditions in the area over a long period of time.

• Mainly temperature and precipitation averages

Trees

• When trees grow a new layer of wood is added each year/season.

• They can tell the age, as well as how the environment was when it grew. ("Dendrochronology")

• Thick ring = lots of water/sunlight/warmth

• Thin ring = poor growing conditions

Multiple Choice

Which side of this tree do you think was getting the most sun?

• Top

• Bottom

• Left Side

• Right Side

Multiple Choice

How would you describe the growth of this tree when it was forming the darker rings?

• Growth is increasing and it is most likely summer

• Growth is increasing and it is most likely fall

• Growth is slowing and it is most likely fall and winter

• Growth is slowing and it is most likely summer

Open Ended

How does studying growth rings in trees limit what we can learn about Earth's changes over time?

Clastic Sediments

Seafloor sediments are "clastic sediments", which are particles that have been eroded and broken down from other rocks and combined with a lot of organic material—skeletons, shells and other remains from creatures that either lived in the water column of the ocean or on the seafloor.

Sediment core samples in storage.

Open Ended

Why do you think scientists want to keep the ocean sediment samples that they collect? Give at least TWO reasons.

Ice

As new snow falls, layers are created for each snow event.

As the layers build they compress on the layers below, eventually compacting into ice layers (like when you make a snow ball).

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Gas bubbles, organisms/traces, chemicals, pollen, dust, volcanic ash, etc... can all be trapped in these layers.

Multiple Choice

What might the thickness of a band tell scientists studying ice cores?

• thick bands may indicate low amounts of precipitation

• thick bands may indicate higher amounts of precipitation

Open Ended

Observe the layers. Notice how they alternate light and dark? Why might the layers of snow/ice be different colors?

• 24 hours of sunlight during the summer, and warmer temperatures, contrasted with 24 hours of darkness and colder temperatures change the texture/color of the ice.

• The "summer ice" is lighter in color than the clear, dark "winter ice".

Gas bubbles provide samples of atmospheric conditions.

National Ice Core Laboratory in Denver, CO

Multiple Choice

A scientist finds fossils of shark teeth in a layer of rock high in the mountains. What could it mean?

• Sharks most likely evolved from land-dwelling mountain animals.

• The fossils were moved there by cavemen.

• The mountain was once under water.

• The shark teeth were carried there by erosion.

Multiple Choice

Upon studying an ice core, a scientist finds that a particular band is very wide. What might explain this?

• Very little precipitation fell that winter.

• Temperatures were colder than normal that year.

• A high amount of precipitation fell that year.

Multiple Choice

The rings in a usually fast-growing type of tree are very close. What does this tell us about the environment that the tree grew in?

• it was an environment with plenty of sunlight, mild temperatures, and moderate precipitation

• it was an environment with colder temperatures, moderate to low sunlight, and little precipitation

Open Ended

How are ice and sediment cores similar to growth rings in a tree?

Multiple Choice

Which of the following would be least helpful for determining the properties of the atmosphere long ago?

• analysis of gas bubbles trapped in sea ice

• analysis of the chemical composition of ocean sediments

• measuring the width of growth rings in a piece of petrified wood

• studying the stomach contents of a frozen/ mummified mastodon