1. Unit 10 Lesson 1 What Are Fossils?
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2. Unit 10 Lesson 1 What Are Fossils?
Traces of the Past
The preserved remains or traces of a living thing is called a fossil.
Fossils can be made of an organism’s hard parts, such as bones, teeth, and shells, or soft parts, which are tissues such as skin and organs.
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3. Unit 10 Lesson 1 What Are Fossils?
Traces of the Past
Most fossils are found in sedimentary rock and can be formed in different ways.
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4. Unit 10 Lesson 1 What Are Fossils?
Traces of the Past
Dead animals at the bottom of a body of water can form fossils. Sediment buries the animal, then soft parts decay and hard parts become fossils.
Minerals, like quartz, can also form fossils by replacing the shell or plant material that made up the organism. This is how petrified wood forms.
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5. Unit 10 Lesson 1 What Are Fossils?
Traces of the Past
Mold and cast fossils are made when an organism, such as a leaf, is pressed into soft mud, leaving a hollow space called a mold.
A cast forms if the mold is later filled with mud that hardens.
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6. Unit 10 Lesson 1 What Are Fossils?
Traces of the Past
All living things contain the element carbon. Some plant tissues get preserved as carbon films in rock.
Footprints are examples of trace fossils. These show that an animal was there, even though none of its parts were preserved.
Scientists study many types of fossils to help them learn about ancient life on Earth.
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7. Unit 10 Lesson 1 What Are Fossils?
Fossils That Burn
Coal forms from dead plants that end up at the bottom of a lake or pond. Sediment buries the plants.
Over years, heavy layers of sediment cause the temperature and pressure underground to rise, changing plant material to coal.
A fossil fuel is an energy-rich resource formed from the buried remains of these once-living organisms.
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8. Unit 10 Lesson 1 What Are Fossils?
Fossils That Burn
Oil and natural gas take millions of years to form from tiny, dead sea organisms at the bottom of the ocean, where they are buried by sediment.
The weight of sediment and water cause temperature and pressure to rise. Hydrogen and carbon are left, forming oil and natural gas.
The oil and natural gas are pumped from the ground.
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9. Unit 10 Lesson 1 What Are Fossils?
Fossils That Burn
Fossil fuels form as once-living organisms are subjected to temperature and pressure changes.
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10. Unit 10 Lesson 1 What Are Fossils?
What Fossils Tell Us
Scientists who study fossils to learn what life on Earth was like long ago are called paleontologists.
Fossils show that some types of plants and animals have changed a lot, while others have hardly changed at all.
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11. Unit 10 Lesson 1 What Are Fossils?
What Fossils Tell Us
For example, the gingko tree, which has been around for at least 420 million years, has not changed much.
Organisms that look as if they have not changed much over time can be called living fossils.
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12. Unit 10 Lesson 1 What Are Fossils?
What Fossils Tell Us
Fish have changed a lot over time. The first fish had no jaws. Later fish developed jaws and heavy armor plates. Today, fish have jaws but no armor.
The woolly mammoth, related to elephants, lived during the Ice Age when the climate was very cold. Today, most elephants live in warm climates.
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