Fossils and Rock Dating and Geological Time Scale

Geologic Time Scale

The Fossil Record!

Fossils

• The surface of Earth is made of layers of rock.

• Each separate layer contains different fossils.

Relative Dating

• Relative dating: "the deeper a fossil is, the older it is"

Absolute Dating

• Absolute dating estimates the age of a fossil in years.

• The age is determined from radioactive chemicals in nearby rocks.

• Method is called "radioactive dating"

Multiple Choice

"Fossil A existed 120 million years ago."

• Absolute dating

• Relative dating

Multiple Choice

"Fossil A is older than Fossil B."

• Absolute Dating

• Relative Dating

Multiple Choice

A 30,000-year-old skull fossil for a saber-tooth tiger was found.

Which process was required in determining the exact age of the fossil?

• radioactive dating

• recrystallization

• relative dating

• superposition

Fossil Record

• All of the fossils that have ever been discovered make up the fossil record.

• Scientists use the fossil record to learn about the species that have existed on earth in the past

• Example: scientists learned about the existence of dinosaurs through the fossil record

Let's look at some examples of what we can learn from the fossil record...

Fossil Record

• The fossil record shows how some populations change over generations.

• For example, fossils show the gradual change in the bodies of horses such as the ones shown to the right (oldest at the bottom, most recent at the top).

Fossil Record

• The fossil record can also show us which species haven't evolved much over time.

• The hard-plated horseshoe crab, for example, has changed little over the last 350 million years.​

Fossil Record

• The fossil record gives evidence of mass extinctions.

• We talked about what it means for a species to go extinct. What do you think a mass extinction is?

Fossil Record

• Mass extinction: when a large number of species goes extinct within a short period of time

• Caused by environmental change (like global warming) or catastrophic events (like an asteroid hitting the earth)

Multiple Choice

The ________ is the total collection of all fossils that have ever been discovered.

• Fossil list

• Fossil record

• Fossil category

• Fossil collection

Fossil Record

• As we discussed, scientists use the fossil record to figure out how organisms have changed since earth was formed, 4.6 billion years ago.

• That's a long time! To organize the different time periods in earth's history, scientists use the geologic time scale.

Geologic Time Scale

• The largest divisions of the geologic time scale are eons. Eons are divided into eras. Eras are further divided into periods, and periods are divided into epochs.

Multiple Choice

How old do Paleontologists believe the Earth is?

• Over 4 billion years

• Over 4 million years

• Over 400,000 years

• Over 4,000 years

1: Precambrian Eon

• Precambrian time covers all of the time from the formation of Earth’s crust to the about 542 million years ago. This represents more than 80 percent of all geologic time.

1: Precambrian Eon

• Covers about 80% of earth's history.

• The very first form of life on earth appeared: bacteria.

• The bacteria used sunlight to make oxygen, which was released into the environment. This allowed other life forms to evolve.

Multiple Choice

The Precambrian Eon represents ____ of all geologic time.

• 10%

• 20%

• 40%

• 80%

2: Phanerozoic Eon

• The Phanerozoic eon stretches from about 542 million years ago to the present. It is divided into three major eras: the Paleozoic, the Mesozoic, and the Cenozoic.

Paleozoic Era

• Animals and plants began to move onto land.

• "Cambrian Explosion" = many new forms of life appeared

• At the end of the era, the largest known mass extinction occurred, wiping out 96% of species in the ocean.

Mesozoic Era

• Called the Age of Reptiles because reptiles dominated the land.

• Dinosaurs appeared during this era, as did birds and small mammals.

• At the end of the Mesozoic, another mass extinction occurred, likely due to an asteroid hitting earth and causing giant dust clouds and wildfires.

Cenozoic Era

• Began about 65.5 million years ago and continues into the present.

• The Age of Mammals - saw the development of early forms of many mammals, including horses and cattle.

• The first human ancestors also appeared.

That was a lot of info! Summary:

• Life began in the ocean (fish were the first animals to exist).

• Eventually, animals and plants began to evolve on land.

• After large dinosaurs went extinct, smaller mammals began to become more dominant.

• Humans ancestors evolved relatively recently.

Multiple Choice

According to fossil evidence, which life form appeared first on Earth?

• amphibians

• fish

• insects

• reptiles

Multiple Choice

During which era did birds and small mammals first appear?

• Cenozoic

• Mesozoic

• Paleozoic

• Proterozoic

Multiple Choice

The table shows details of a portion of the Paleozoic Era.

What can be concluded about the Paleozoic Era?

• During this era, a large diversity of life forms appeared.

• In the middle of this era, period extinction of life forms occurred.

• At the beginning of this era, organisms were able to make their own food.

• During this era, invertebrates were the dominant group of organisms.

Multiple Choice

A paleontologist is having difficulty discovering the fossils of the earliest cnidarians, which include present-day organisms such as sea anemones, coral, jellyfish, box jellies, and hydra, from about 580 million years ago. What is the likely reason the paleontologist is having difficulty finding fossils of the earliest cnidarians?

• The earliest cnidarians did not live in aquatic environments.

• The earliest cnidarians might not have developed mineralized hard parts that fossilize easily.

• The population of early cnidarians was lower than in present day.

• The oceans lacked enough sediments for fossil formation of early cnidarians to occur.

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