Earth Science: Geologic Time How Old Is the Earth?
Exploring Earth's 4.6 billion year history
Earth Science: Geologic Time How Old Is the Earth?
Exploring Earth's 4.6 billion year history
Earth Science - Grade 4-5
- 1
Scientists estimate that Earth is about 4.6 billion years old. Write this age in standard form using digits.
One billion is written as 1,000,000,000.
Earth is about 4,600,000,000 years old in standard form. - 2
Explain why scientists use the phrase geologic time when talking about Earth's history.
Scientists use the phrase geologic time because Earth's history is extremely long and includes events that happened millions or billions of years ago. - 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?
Compare the whole timeline to the tiny section near the present.
This tells me that humans have lived on Earth for only a very small part of Earth's long history. - 4
Put these events in order from oldest to most recent: dinosaurs live on Earth, Earth forms, first humans appear, first simple life appears.
The correct order is Earth forms, first simple life appears, dinosaurs live on Earth, and first humans appear. - 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.
Think about stacking papers one at a time on a desk.
The bottom layer is usually the oldest because it was laid down first, and newer layers formed on top of it. - 6
A fossil is found in a very old rock layer. What can the fossil help scientists learn?
The fossil can help scientists learn what kinds of living things existed long ago and what the environment may have been like. - 7
Choose the better unit for measuring the age of Earth: days, years, millions of years, or billions of years. Explain your choice.
Use a unit that makes a very large age easier to understand.
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. - 8
If Earth were represented by a 100-page book, and humans appeared on the last page, what does that model show?
The model shows that humans appeared very late in Earth's history compared with the age of the planet. - 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?
New sediment usually settles on top of older sediment.
Layer B is older because it is below Layer A, and lower layers usually formed before the layers above them. - 10
Describe one reason it is hard for people to imagine 4.6 billion years.
It is hard to imagine 4.6 billion years because human lives are much shorter, and most people only directly experience a few decades. - 11
A fossil of a sea animal is found in rock high in a mountain. What might this suggest about that area long ago?
Think about where sea animals normally live.
This might suggest that the area was once covered by an ocean or shallow sea before it became part of a mountain. - 12
What is the main difference between relative age and exact age in geology?
Relative age tells whether something is older or younger than something else, while exact age gives a number of years. - 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.
For ages of rocks, the larger number usually means the rock formed longer ago.
The 200-million-year-old rock is older because 200 million years is a longer time ago than 50 million years. - 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?
The Mesozoic should be labeled the Age of Dinosaurs because dinosaurs lived during that section of geologic time. - 15
Write a short explanation of how rock layers, fossils, and timelines help scientists understand how old Earth is.
Include all three ideas: rock layers, fossils, and timelines.
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.