fossils

rock layers and the age of fossils

There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought.

textbook_image

textbook_image

textbook_image

the fossil record

Fossils are the preserved remains of animals, plants, and other organisms from the distant past. Examples of fossils include bones, teeth, and impressions. By studying fossils, evidence for evolution is revealed. Paleontologists are scientists who study fossils to learn about life in the past. Fossils allow these scientists to determine the features of extinct species. Paleontologists compare the features of species from different periods in history. With this information, they try to understand how species have evolved over millions of years ( Figure below). Until recently, fossils were the main source of evidence for evolution ( Figure below). Through studying fossils, we now know that todays organisms look much different in many cases than those that were alive in the past. Scientists have also shown that organisms were spread out differently across the planet. Earthquakes, volcanoes, shifting seas, and other movements of the continents have all affected where organisms live and how they adapted to their changing environments.

instructional diagrams

No diagram descriptions associated with this lesson

questions

fossils are the preserved remains of animals, plants, and other organisms from the distant past.

-->  a. true

b. false

fossiltologists are scientists who study fossils to learn about life in the past.

a. true

-->  b. false

which best describes radiometric dating?

a) measures the accumulation of radiometric materials in a sample.

-->  b) measures the breakdown of radioactive materials in a sample.

c) dates material by measuring radiometric samples.

d) dates material by measuring the breakdown of radioactive samples.

which statement describes the order of materials in the fossil record?

a) newer layers form on top of the older layers.

-->  b) newer fossils form on top of the older fossils.

c) older fossils form on top of the newer fossils.

d) older layers form on top of the newer layers.

the oldest rocks on earth are

a) 1 billion years old.

-->  b) 5 billion years old.

c) between 3 and 4 billion years old.

d) between 4 and 5 billion years old.

the fossil record provides evidence for

a) when organisms lived on earth.

b) how some species have gone extinct.

c) how species evolved.

-->  d) all of the above

the oldest fossils on earth are

a) 1 million years old.

b) 1 billion years old

-->  c) between 3 and 4 billion years old.

d) between 4 and 5 billion years old.

diagram questions

No diagram questions associated with this lesson