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Ch. 8 - Lesson 1: How fossils help us know about Earth's history.
Transcript of Ch. 8 - Lesson 1: How fossils help us know about Earth's history.
Fossils of animals and
plant remains help us
understand Earth's history. Lesson 1 Essential Question:
What do fossils
show about Earth's history and how
are they formed? Scientists believe that the Earth
formed about 4.5 billion years ago.
Over time the outer layer of Earth
has hardened, forming the crust.
Volcanoes have spewed lava, ash and gases all over the planet. The atmosphere contained no oxygen and oceans began to form. Scientists also theorize
that about 3.5 billion years
ago, the first living things
appeared here on Earth. Over millions of years, other organisms
developed. Many of these no longer exist,
so how do we know about them? We know many details about
Earth's history from clues scientist
have taken from fossils. A fossil is the preserved remains
or traces of a living thing. Fossils show us how
organisms and Earth
itself have change over time. Fossil Formation When organisms die, they
usually are eaten or decay quickly. Sometimes remains are buried in sediment, ice or tree sap. These remains may become fossils. Sometimes organisms or parts of
organisms become petrified. Molds and cast preserve
the shape of organisms.
Both begin when hard
remains are buried in sediment.
The sediment hardens into rock,
and the hard remains dissolve. A mold is the hollow space that is
left when sediment hardens around
the remains of an organism and
the remains then dissolve. A cast is a fossil that is formed when
dissolved minerals fill a mold and harden. Sometimes an entire animal is preserved. Insects, spiders, and even lizards have been trapped in tree sap. The tree sap hardened into amber. Scientists
have found huge mammoths buried in ice and snow.
The ice preserved their bodies. Trace fossils are evidence
of an animals's activities. 1st The animal makes tracks
or burrows. 2nd The tracks
or burrows harden in mud. 3rd The mud becomes rock
over millions of years. Scientists use trace fossils to
estimate the size of an animal. A carbon film is an extremely
thin coating of carbon. A carbon film forms when heat
and pressure force out most of
the remains of a buried organism. What is left is a thin film
of carbon that shows the
organism or some part
of it in fine detail. An index fossil helps scientist
find the age of a rock layer. Index fossils come from
organisms that lived in may
places around the world
during a brief period of time. Each type of index fossil
formed at only one particular
time. So index fossils provide
a way to match rocks of
the same age found
in different places. Index fossils can help scientists determine the absolute age(age of the rock in years)
of a rock. Since each type of index
fossil formed at only one time, the
rock around such a fossil must have
formed around that same time. Scientists examine the elements
found in different rocks and fossils.
Some of these elements change in
form or amount over a long period of
time. By knowing how long these
changes take, scientists can find
the absolute age of a rock or fossil. Fun Facts Mary Anning
"She sells seashells by the seashore." Have you ever tried to say that three times fast?
Mary Anning, who inspired that tounge twister, grew up in the early 1800's on the coast of England. She noticed that fossil collectors were selling fossil shells for high prices, so she began collecting shells to sell in her father's souvenir shop.
Mary was only 12 when she discovered her first skeleton (a dolphinlike reptile called an ichthyosaur). The skeletons of prehistorice marine fossils that Mary Anning found are now on display in museums all over the world. The Misnamed Dino
Sometimes paleontologists do put skeletons together incorrectly. In 1879, famous fossil hunter O.C. Marsh found parts of a huge skeleton in Wyoming. He was in a big hurry to put it together and name it before his rival, Edward Drinker Cope, found out. But it was missing a lot of pieces, including the skull. Marsh drew a picture of the complete skeleton, adding a head found not very far away that looked as if it would fit with the body. He then named this new dinosaur Brontosaurus.
About 25 years later, another paleontologist
showed that the Brontosaurus was actually
same species of dinosaur as the Apatosaurus,
which Marsh had discovered and named two
years earlier. Many people still incorrectly
refer to the Apatosaurus as Brontosaurus.
In the 1970's paleontologist Jack McIntosh
realized that Marsh had used the head of the
Camarasaurus. This mistake has been corrected,
but for about 100 years, models were shown in
museums with the wrong head!!!
(There is no dinosaur called Brontosaurus.) Fossils show us how Earth itself has changed. For example, similiar fossils have been found on both sides of the Atlantic Ocean. Many of the organisms that left these fossils could not have crossed the ocean. The finding of these fossils
in distant places supports the
theory of continental drift. Continental drift is the theory
that the continents have
been slowly drifting apart
for millions of years. According to this theory, about
225 million years ago, all of Earth's
landmasses were joined. This huge landmass is now
called Pangea (pan-jee-uh)