Fossils
In the Generation
Genius video above, you will examine specimens from the fossil record and formulate claims based on evidence about how
organisms have changed over time.
Why
Fossils Matter
Watch the video below, then complete the
following questions in your science journal.
In your science
journal,
answer the following questions.
1. How do we know so much about plants and
animals that lived millions of years ago?
2. What is the definition of a
"fossil?"
3. What is the study of
ancient beings?
Fossil and chemical analysis establish the
Earth's age at about 4.6 billion years.
Fossils are the remains of ancient life
preserved in Earth's crust. Most
people think of fossils as preserved bones or shells of primitive animals.
However, there are many forms of fossils. Scientists have even found fossil
impressions of early forms of bacteria.
The term fossil derives
from a Latin word meaning "to dig." The scientific study of fossils
is called paleontology from the
Greek meaning the science of very old existing things.
In this unit, you will learn how fossils provide
important evidence of how life and environmental conditions have changed.
Let's Practice
What is
the Fossil Record?
Fossil-containing
strata
Fossils help geologists
establish the ages of layers of rock. In this diagram, sections A and B
represent rock layers 200 miles (320 km) apart. Their ages can be established
by comparing the fossils in each layer.
A fossil is a trace of an organism from the past, such as a
skeleton of a fish or a leaf imprint, embedded and preserved in Earth's crust.
Earth's crust is its outermost layer made of rock.
Most fossils are dug up from sedimentary rock layers. Sedimentary
rock is formed from sediment, like sand, mud, or small pieces of rock. Over
long periods, sediment is squeezed together as they are buried under more
layers that pile up. Eventually, those sediments are compressed into
sedimentary rock. The layers father down in Earth's crust are older than the
upper layers.
Layers of sedimentary
rock.
In your science
journal, answer the following
questions using the image above.
1. Which fossils are the
oldest?
2. Which fossils are the youngest?
Many fossils are formed from the hard part of
an organism's body, like bones and teeth. Fossil
formation begins when an organism's body is quickly covered in sediment
from an event like a mudslide. Over time, more and more sediments cover the remains.
The body parts that do not rot are buried under layers of sediments. After a
long time, the organic compounds in the body parts are replaced with rock-like
minerals. This process results in a heavy, rock-like copy of the original
object --- a fossil.
Fossils are evidence of past life. Fossils
found and placed in chronological order are part of "The Fossil Record." Scientists examine the fossil record for
patterns that indicate when ancient organisms lived and how they are related.
Fossils found in rock at the bottom of a sequence of layers are older than the
fossils found near the top of the sequence.
Let's Practice
Watch the Generation
Genius video at the top of this unit, then complete the Let's Practice.
What is
the Geologic Time Scale?
Scientists have developed a model of the
history of life on Earth called the geologic time scale.
The geologic time scale.
In your science
journal,
answer the following questions based on the geologic time scale image.
1. What is the oldest era on the geological time
scale?
2. What is the current era on the geological time
scale?
3. Why is it important for scientists to use a
geological time scale?
The geologic time scale is based on studies of
Earth's geology and the fossil record.
The geologic time scale is divided from longer
to shorter lengths of time, from eons
to eras to periods. Most time scales commonly name eras and periods.
·
Eras are determined by the dominant life forms
present at the time.
·
Periods are smaller blocks of time based on eras;
periods are based on types of fossils found within each era.
The video below communicates the history of
Earth in terms of its geologic time scale. The segment identifies the history
of Earth into the Precambrian, Paleozoic, Mesozoic, and Cenozoic Eras.
|
Era |
Years Ago |
Characteristics |
|
Cenozoic |
65 million – current |
·
Scientists
have the most information about life in this era ·
Called
the Age of Mammals |
|
Mesozoic |
251 million – 65 million |
·
Called
the Age of Reptiles (Dinosaurs) ·
Flowering
plants evolved ·
Geological
evidence indicates an asteroid may have hit the Earth, causing extinctions. |
|
Paleozoic |
542 million – 251
million |
·
Fossils
of snails, clams, and corals ·
Glaciers
covered the Earth ·
Fishes
with backbones appeared ·
Plants
and air-breathing animals began to populate the land |
|
Precambrian |
4.6 billion – 542
million |
·
The
first prokaryotic cells appeared ·
Photosynthetic
bacteria evolved and began to add oxygen to Earth's atmosphere ·
The
ozone layer blocked harmful radiation from the sun allowing life to move out
of the water and onto dry land |