Fossils & History of Life

Chapter 12 Biology

Science 101

• United streaming—fossils 59sec clip

VestigialStructures

Comparative

Anatomy

Convergent

EvolutionFossilRecord

This is the Home Page

From the Home Page, you can investigate several lines of evidence that support the Theory of

Evolution.

Click any box to enter that area.Fossil Record is a

good place to start

Embryological

Development

MolecularComparison

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Evidence ofEvolution

Evidence ofEvolution

MolecularComparison

s Embryological

Development

Convergent

EvolutionFossilRecord

Comparative

Anatomy

VestigialStructures

KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.

Fossil Record

• Fossil Facts:– A fossil is any part or trace of a once-living organism.

• It may be bones, but there are other types of fossils.– Click one of the items below to learn more about the different

types of fossils.

Trace FossilsAmber

Molds/CastingsPetrified Wood

Frozen Organisms

Imprints

Fossilized Bones

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• Fossil Record

Fossils can form in several ways.

• Permineralization occurs when minerals carried by water are deposited around a hard structure.

Molds/Castings

• Molds and castings form when the hard shell or exoskeleton of an organism is buried in sediment.

• The sediment hardens around the body, then the body dissolves or decomposes, leaving a void or mold.

• The mold can fill with minerals to form a cast in the shape of the mold.

Casting of a fossil trilobite

Trace fossils include burrows, tracks, even fossilized poop!

Fossil burrows Dinosaur tracks Dinosaur & Fish Poop

• Trace fossils record the activity of an organism.

Imprint Fossils• When plants and animals fall in fine sediments, their bodies can sometimes

leave an imprint that shows up when the resulting rock layers are split apart.

Clockwise from left - The imprints of feathers can be seen in the Archaeopteryx fossil. A dragonfly imprint in the same fine sediment bed. The delicate imprint of an extinct fern’s frond.

• A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

Fossil Bones• Bones and teeth of vertebrates are resistant enough to remain intact when

the rest of the body has decayed. • Dinosaur skeletons are among the most spectacular fossils ever found.

A 12,000 year old mammoth skeletonSue, the largest, most complete T. rex fossil ever found. It resides at the Field Museum in Chicago.

• Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

Amber• Amber is fossilized tree sap. It often traps pollen, insects and other small

animals.

Insects trapped in amber.

Petrified Wood• When wood is buried in ash or sandy sediments, silica can form within the

wood structure, eventually replacing the organic material.

These petrified logs are found at Petrified Forest National Park in Arizona.

• Preserved remains form when an entire organism becomes encased in material such as ice.

Frozen Organisms• In some places, animals and plants get trapped in snow and are preserved for

thousands of years. • This obviously happens only in cold mountainous and polar areas.

Above - Otzi, the famous “Ice Man” found frozen in the Italian Alps

Left - Dima, a baby mammoth found preserved in the Siberian permafrost by Russian miners.

• Specific conditions are needed for fossilization.• Only a tiny percentage of living things became fossils.

Radiometric dating provides an accurate way to estimate the age of fossils.

• Relative dating estimates the time during which an organism lived.– It compares the placement

of fossils in layers of rock.– Scientists infer the order in

which species existed.

• Radiometric dating uses decay of unstable isotopes.– Isotopes are atoms of an element that differ in their number of

neutrons.

neutrons protrons

– A half-life is the amount of time it takes for half of the isotope to decay.

• Radiometric dating uses decay of unstable isotopes.

– Isotopes are atoms of an element that differ in their number of neutrons.

Index fossils are another tool to determine the age of rock layers.

• Index fossils can provide the relative age of a rock layer. – existed only during specific spans of time– occurred in large geographic areas

• Index fossils include fusulinids and trilobites.

If evolution had not occurred, click the statement below that should be true about the fossil record.

• Different rock layers should contain different fossil species.

• Younger (shallower) rock layers should contain fossils that look more like modern organisms.

• Most rock layers should contain fossils of species that are not alive today.

• Every rock layer should contain fossils that look exactly the same.

That’s right.

• If every species had always been present in its current form, then we should be able to find fossils of all modern species -- from bacteria to bats -- in every layer of rock.

• It wouldn’t matter how deep you dig -- if modern species were living from the very beginning of earth’s history, then some fossil evidence should exist even in the oldest rocks. It doesn’t.

• By itself, the fossil record provides strong evidence that evolution has occurred.

Actually, this statement should be correct if evolution has occurred.• Think about what it means for things to evolve.

• Evolution refers to the change that happens in species over time.

• Go back and try to pick out the statement that should be true if things NEVER changed.

Conclusion:• The fossil record shows a progression from simple life forms to more complex,

modern-looking forms.

• The only logical explanation is that life has evolved from a single life form into the diversity we see here today.

View flim clip biology textbook

• Geologic Time

The geologic time scale organizes Earth’s history.

• The history of Earth is represented in the geologic time scale.

100250

550

1000

2000

PRECAMBRIAN TIME

Cyanobacteria

This time span makes up the vast majority of Earth’s history. It includes the oldest known rocks and fossils, the origin of eukaryotes, and the oldest animal fossils.

• Eras last tens to hundreds of millions of years.– consist of two or more periods– three eras: Cenozoic, Mesozoic, Paleozoic

• Periods last tens of millions of years.– most commonly used units of time on time scale– associated with rock systems.

• Epochs last several million years.

Palazoic film clip

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