Download The History of Life On Earth

McDougall Littell
The History Of Life
 Fossils provide evidence about the history of life on
Earth.
 Most fossils are hard body parts or bone. Others form
when minerals replace the remains of organisms.
 Fossils also include prints left by organisms, such as
footprints.
 Very rarely, a fossil is the preserved remains of an
organism, such as a wooly mammoth in ice or an insect
preserved in sap.
The History of Life
 Relative age is how old a rock or fossil is compared to
other rocks or fossils.
 Ancient organisms settled to the bottom of a body of
water in layers of mud and sand that later formed
rock.
 A fossil found in a deeper layer of rock is usually older
than a fossil found in a layer of rock near the top.
The History of Life
 Absolute age is the actual age of the rock or fossil.
 To measure the absolute age of a fossil, scientists
measure its radioactivity.
 Over time, radioactive material disappears.
 The older the fossil, the less radioactive material it has.
The History of Life
 The fossil record is all of the information that can be
gathered from the fossils in a particular location.
 Scientists can then use the record to identify which
species lived and died during different periods of time.
The History of Life
 Scientists can use technology to dig deep into the
ground to recover fossils and other information to
reconstruct the ancient past.
 http://www.classzone.com/books/earth_science/terc/
content/visualizations/es2901/es2901page01.cfm
More Complex Organisms Developed Over the
Course of Earth's History.
 Unicellular organisms, made of only one cell, were the
first living things on Earth.
 They appeared about 3.8 billion years ago.
 The atmosphere then did not have as much oxygen as
it does now.
 Some of the early organisms added oxygen to the
atmosphere.
More complex organisms developed over the
course of Earth's history.
 Multicellular organisms began to live in Earth's oceans
about 1.2 billion years ago.
 Multicellular organisms have many cells that perform
different tasks within the same body.
 The fossil record shows that the earliest multicellular
organisms were tiny seaweeds.
 The earliest animals were similar to jellyfish.
The History of Life
 Life appeared on land about 500 million years ago.
Before that, all living things met their needs while
living in water.
 Simple plants were the first land-dwelling organisms,
getting water from the soil through roots.
 The plants in turn provided food and shelter to the
first fungi and insects on land.
 After insects, amphibians and reptiles began to live on
land, followed by birds and mammals.
The History of Life
 A species becomes extinct when all members of the
species have died.
 Many species have only been seen as fossils because
they became extinct long ago.
 A mass extinction is a period when a large number of
species become extinct in a very short time.
The History of Life
 The Permian Extinction occurred about 250 million
years ago.
 Approximately 90 percent of the species in the ocean,
as well as many land-dwelling animals, became
extinct.
 This mass extinction may have been caused by climate
change due to all of Earth's landmasses joining
together to form a single, enormous continent.
The History of Life
 The Cretaceous Extinction occurred about 65 million
years ago.
 More than half of all the species on Earth, including
dinosaurs, became extinct.
 This mass extinction may have been caused by a
meteorite, a giant space object, colliding with Earth.
The meteorite left a
200 km-wide crater
off the Yucatán
peninsula in Mexico
The History of Life
 Mass extinctions are often followed by the appearance
of a large number of new species.
 For example, the extinction of dinosaurs may have
allowed new species of mammals to develop and
thrive.