Fossils Fossil Record

Fossil Evidence and

Geologic Time Scale​

By Karen Lolli

Earth's early history

The Earth contains clues, which give us information its formation

• Earth formed 4.5 billion years ago

• Covered in volcanoes and lava

• Atmosphere full of toxic gases

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Life could not have survived the intense heat & lack of O₂ on the early Earth

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Estimated that life formed ~3.5 billion years ago, after the Earth cooled​

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Multiple Choice

How long ago did the Earth form?

• 4.5 billion years

• 3.5 billion years

• 4.5 million years

• 3.5 million years

Multiple Choice

How long ago did life first form on Earth ?

• 4.5 billion years

• 3.5 billion years

• 4.5 million years

• 3.5 million years

fossils

​Fossil - any preserved evidence of an organism

• plants, animals, bacteria, footprints, leaves

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99% of all species to ever live on Earth are extinct

• ​most decompose before they can become fossils

• only a small percent are preserved in fossils​

  • the organism must be buried in sediment quickly after dying

  • occurs more with organisms living in water

Multiple Choice

Most ancient organisms.....

• become fossils

• decompose and do not become fossils

Multiple Choice

____% of all organisms that lived on Earth are extinct

• 99

• 89

• 49

• 29

Fossil formation

Fossils can only form in sedimentary rock

1. organism dies

2. covered by sediment (mud/dirt)

3. minerals fill in the holes in the bones OR the bones leave an impression in the sediment

4. sediment hardens into rock

5. erosion uncovers the fossil millions of years later​

Multiple Choice

Fossils can only form in ____________ rock

• sedimentary

• igneous

• metamorphic

The fossil record - 6 types of fossils

1. Trace fossil - indirect evidence of an organism, like a footprint

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2. Molds and casts​ - an impression of an organism (mold), sometimes filled in with sediment (cast)

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3. Replacement - original material from an organism is replaced with mineral crystals​

Multiple Choice

A dinosaur footprint is an example of a ________ fossil

• mold

• cast

• replacement

• trace

Multiple Choice

An impression left in sediment, filled in with sediment is called a ______________ fossil

• trace

• mold

• cast

• replacement

The Fossil record - 6 types of fossils

5. Petrified - empty holes in wood are filled in with minerals

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6. Amber - an organism is preserved in tree sap

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5. Original material - natural mummification or freezing​ preserves the original organism

Multiple Choice

A ancient bug trapped in tree sap is called ____________ fossil

• petrified

• amber

• original material

Multiple Choice

An ancient animal that is frozen in ice, preserving its entire body, is called ____________ fossil

• petrified

• amber

• original material

Analyzing fossils

Paleontologist - scientist who studies fossils

• ​diet of the animal

• environment it lived in

• image of original organism

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​Geologist - scientist who studies rocks

• rock layers of the same age, on different parts of Earth, contain same kind of fossils

Multiple Choice

Paleontologists study fossils, and geologists study rocks

• True

• False

dating fossils

Relative dating - determines the age of rocks by comparing them to other layers of rock

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Law of Superposition - young rocks on top, older rocks deeper

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Radiometric dating - uses the decay of radioactive isotopes to measure the age of rocks

• cannot be used on sedimentary rocks

• geologist use this method to measure age of rocks above and below the fossil (like in the virtual lab)

  • provides a range of dates, but not an exact date of the fossil

Multiple Choice

The Law of Superposition says that older rocks are found

• in the deeper rock layers

• in the rock layer on top

Multiple Choice

Radiometric dating provides a(n) ________________ of a fossil found in sedimentary rock

• range of dates

• exact age

Geologic Time Scale

A record of Earth's history based on geological and biological evidence

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GTS is broken down into sub-divisions

• Eon - billions of years

• Era - 100s of millions of years

• Period - 10s of millions of years

• Epoch - several million years​

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Geologic Time Scale

Fill in the Blanks

On the Geologic Time Scale, what is the longest length of time called?

Multiple Choice

About how long is an Era?

• billions of years

• 100s of millions of years

• 10s of millions of years

• several million years

Precambrian

First 4 billion years of Earth's history (90% of total time)

• ​From the formation of Earth to 542 million years ago

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Life first appeared​

• ​autotrophic prokaryotic cells

• eukaryotic cells​

• ​ocean creatures

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Multiple Choice

About how long does the Pre-Cambrian last for?

• 1 billion years

• 2 billion years

• 3 billion years

• 4 billion years

Multiple Choice

During the Pre-Cambrian, life first appeared on earth

• true

• false

Paleozoic Era

488-251 million years ago

Ancestors of most major animal groups emerged = Cambrian Explosion = explosion of diversity of life

• ​Major changes in ocean life​

  • sharks, fish, coral

• ​Land organisms emerged​

  • plants, bugs, vertebrates, amphibians, reptiles​

Paleozoic Era

Had 2 mass extinctions - ~60-70% of species became extinct in a short time​

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Ended with another mass extinction​ ~90% ocean life

• due to volcanic activity​

Multiple Choice

The Cambrian Explosion refers to an "explosion" of _____________

• rocks

• life

• oxygen

• ocean water

Multiple Choice

A mass extinction is when the majority of species ______________

• adapt

• die

• migrate

• reproduce

Multiple Choice

About _____% of ocean species went extinct at the end of the Paleozoic Era

• 90

• 80

• 70

• 60

Mesozoic Era

250-65 million years ago

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Dominated by dinosaurs, flowering plants, birds, reptiles

• early mammals first appeared​

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​Ended with mass extinction from meteorite impact on Earth

• Layer of rock called the KT Boundary contains iridium - mineral rare on Earth but common in meteorites

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Continents shifted greatly, also causing extinctions

Multiple Choice

The Mesozoic Era was dominated by

• dinosaurs

• bugs

• humans

• mammals

Multiple Choice

The Mesozoic Era ended with a mass extinction, mainly cause by ___________

• a meteorite

• volcanic activity

• ice age

Cenozoic era

65 million years ago to present

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Dominated by land mammals​

• wooly mammoth, saber tooth tiger, primates

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Humans appear at the very end ~​ 11,000 years ago, after the last ice age

Multiple Choice

Which type of organisms dominated the Cenozoic Era?

• ocean creatures

• dinosaurs

• land mammals

• birds

Multiple Choice

Humans appeared on the Geologic Time Scale about ____________ years ago

• 11 million

• 110,000

• 11,000

• 1,100