Earth Science: Geologic Time How Old Is the Earth? Worksheet

Question 1

Scientists estimate that Earth is about 4.6 billion years old. Write this age in standard form using digits.

Accepted Answer

Earth is about 4,600,000,000 years old in standard form.

Question 2

Explain why scientists use the phrase geologic time when talking about Earth's history.

Accepted Answer

Scientists use the phrase geologic time because Earth's history is extremely long and includes events that happened millions or billions of years ago.

Question 3

A timeline shows Earth forming 4.6 billion years ago and the first humans appearing much closer to today. What does this tell you about humans in Earth's history?

Accepted Answer

This tells me that humans have lived on Earth for only a very small part of Earth's long history.

Question 4

Put these events in order from oldest to most recent: dinosaurs live on Earth, Earth forms, first humans appear, first simple life appears.

Accepted Answer

The correct order is Earth forms, first simple life appears, dinosaurs live on Earth, and first humans appear.

Question 5

Rock layers are often stacked on top of each other. In an undisturbed stack of rock layers, which layer is usually the oldest: the top layer or the bottom layer? Explain.

Accepted Answer

The bottom layer is usually the oldest because it was laid down first, and newer layers formed on top of it.

Question 6

A fossil is found in a very old rock layer. What can the fossil help scientists learn?

Accepted Answer

The fossil can help scientists learn what kinds of living things existed long ago and what the environment may have been like.

Question 7

Choose the better unit for measuring the age of Earth: days, years, millions of years, or billions of years. Explain your choice.

Accepted Answer

Billions of years is the better unit because Earth is so old that smaller units like days or regular years would make the number very large.

Question 8

If Earth were represented by a 100-page book, and humans appeared on the last page, what does that model show?

Accepted Answer

The model shows that humans appeared very late in Earth's history compared with the age of the planet.

Question 9

A scientist finds two rock layers. Layer A is above Layer B. The layers have not been folded or flipped. Which layer is older, and why?

Accepted Answer

Layer B is older because it is below Layer A, and lower layers usually formed before the layers above them.

Question 10

Describe one reason it is hard for people to imagine 4.6 billion years.

Accepted Answer

It is hard to imagine 4.6 billion years because human lives are much shorter, and most people only directly experience a few decades.

Question 11

A fossil of a sea animal is found in rock high in a mountain. What might this suggest about that area long ago?

Accepted Answer

This might suggest that the area was once covered by an ocean or shallow sea before it became part of a mountain.

Question 12

What is the main difference between relative age and exact age in geology?

Accepted Answer

Relative age tells whether something is older or younger than something else, while exact age gives a number of years.

Question 13

A rock sample is 200 million years old. Is it older or younger than a rock sample that is 50 million years old? Explain.

Accepted Answer

The 200-million-year-old rock is older because 200 million years is a longer time ago than 50 million years.

Question 14

Look at a geologic time scale with four sections: Precambrian, Paleozoic, Mesozoic, and Cenozoic. Dinosaurs lived during the Mesozoic. Which section should be labeled the Age of Dinosaurs?

Accepted Answer

The Mesozoic should be labeled the Age of Dinosaurs because dinosaurs lived during that section of geologic time.

Question 15

Write a short explanation of how rock layers, fossils, and timelines help scientists understand how old Earth is.

Accepted Answer

Rock layers show the order of events, fossils show what life existed in the past, and timelines organize these clues to help scientists understand Earth's very long history.

Earth Science: Geologic Time How Old Is the Earth?

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