Science Chapter 10 - terms
describe the process by which fossils form
A living thing dies and is buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. They are usually found in sedimentary rock.
carbon-14 dating
A radioactive form of carbon is carbon-14. All plants and animals contain carbon and some carbon 14. As plants and animals grow, carbon atoms are added to their tissues. Once they die, no more carbon is added and the carbon-14 in the organism's body decays. It changes to stable nitrogen-14. Scientists measure the amount of carbon-14 that is left in the organism's remains to determine the absolute age of the organism. Can only date materials from organisms that lived up to 50,000 years ago because carbon-14 only has a half life of 5,730 years.
geologic time scale
A record of the life forms and geologic events in Earth's history.
What is a cast fossil and how does it form?
A solid copy of the shape of an organism. It forms when water carrying dissolved minerals and sediment seep into the empty space of a mold and deposits minerals and sediment there. A cast is the opposite of its mold.
How does a carbon film form?
All living things are made of carbon. When sediment buries an organism, some of the materials that make up the organism evaporate or become gases. These gases escape from the sediment leaving carbon behind. Over time, only a thin layer of carbon remains. This process can preserve delicate parts of plant leaves and insects.
fossil record
All of the information that paleontologists have gathered about the past life of an organism. It provides evidence about the history of life and past environments on Earth. It also shows that different groups of organisms have changed over time.
What are most fossils formed from
Animals or plants that once lived in or near quiet water such as swamps, lakes, or shallow seas where sediments build up.
What are the hard parts of a fossil organism made up of
Bones, shells, teeth, seeds and woody stems
Carbon films
A fossil with an extremely thin coating of carbon on rock.
What is a mold fossil and how does it form?
A hollow area in sediment in the shape of an organism or part of an organism. It forms when the hard part of the organism such as a shell is buried in sediment.
Precambrian Time
Covers 88% of Earth's history and ended 544 million years ago.
periods
Eras are subdivided into these units of geologic time
What is the name of the theory that describes and explains the change of organisms over time
Evolution
What things expose a fossil at the surface
weathering and erosion
extinct
when a type of organism no longer exists and will never live on Earth again
element
when all atoms in a particular type of matter are the same the matter is this
Why do only hard parts of an organism generally leave fossils
Soft parts of an organism decay quickly or are eaten by animals when an organism dies. It is rare that a soft part of an organism becomes a fossil.
preserved remains
Some organisms are preserved by their remains being trapped in tar (sticky oil that seeps from Earth's surface), some are preserved in amber (the hardened resin or sap of evergreen trees), and some are preserved in ice by water freezing.
What is a petrified fossil
Fossils in which minerals replace all or part of an organism. An example is petrified tree trunks.
index fossil
Fossils of widely distributed (come from many different areas) organisms that lived briefly during only one short period. They help geologists match rock layers.
trace fossils
Fossils that provide evidence of the activities of ancient organisms. An example is a fossilized footprint of a dinosaur, a trail or burrow.
How do geologists find the relative age of a fault
Geologists find the relative age of the youngest layer cut by the fault
half life
In a radioactive element, the time it takes for half of the radioactive atoms to decay. The rate of decay is constant and never changes in each radioactive element.
When did the Paleozoic Era begin
It began 544 million years ago and lasted for 300 million years.
When did the Mesozoic Era begin
It began about 245 million years ago and lasted about 180 million years. People called this era the Age of Reptiles.
When did the Cenozoic Era begin
It began about 66 million years ago and continues to the present. Mammals became common during this time
What does the fossil record show us about how organisms changed over time
It shows us about past environments, the past climate of a region, and changes in the Earth's surface.
Name the kinds of fossils
Molds and casts, petrified fossils, carbon films, trace fossils, or preserved remains
When did Earth form
Scientist hypothesize that Earth formed at the same time of the other planets and the sun , about 4.6 billion years ago
potassium-argon dating
Scientists date rocks using this. This form of potassium decays to stable argon 40 and has a half life of 1.3 billion years. It is useful in dating the most ancient rocks because of its long half-life.
continental drift
Scientists have found that the continents move very slowly over Earth's surface because of forces inside the Earth.
What is necessary for a fossil to form?
The remains or traces of an organism must be protected from decay. Several processes may cause a fossil to form that include fossils found in rocks such as molds and casts, petrified fossils, carbon films, and trace fossils. Other fossils form when the remains of organisms are preserved in substances such as tar, amber, and ice.
Why does radioactive dating work well for igneous rock but not sedimentary rock
The rock particles in sedimentary rocks are from other rocks all of different ages. Radioactive dating would provide the age of the particles but would not provide the age of the sedimentary rock.
Eras
The time between Precambrian Time and the present. Geologists divide this time into three of these.
Why are 2 reasons why ammonite fossils make good index fossils
They are widely distributed and many different types of ammonites evolved and then became extinct after a few million years
When do scientists believe life began on Earth
They cannot pinpoint when or where life began on Earth. They have found fossils of single celled organisms in rocks that formed about 3.5 billion years ago. These earliest life forms were probably similar to present day bacteria.
What do paleontologists do
They collect fossils from sedimentary rocks all over the world. They use this information to determine what past life forms were like. They try to learn what these organisms ate, what ate them, and in what type of environment they lived. They also classify organisms and group similar organisms together and arrange organisms in the order in which they lived.
How do scientists date sedimentary rock layers?
They date the igneous intrusions and extrusions near the sedimentary rock layers.
What characteristics must a fossil have to be useful as an index fossil?
To be useful as an index fossil a fossil must be widely distributed (come from any different areas) and represent a type of organism that existed or lived only briefly.
What are 3 ways that the remains of an organism can be preserved with little change?
Trapped in tar, amber, or in ice (freezing)
Radioactive dating
What geologists use to determine the absolute ages of rocks. Scientists first determine the amount of a radioactive element in a rock. Then they compare that amount with the amount of the stable element into which the radioactive element decays.
radioactive decay
When some elements that exist in an unstable form break down or decay by releasing particles and energy in this process. During this process the atoms of one element break down to form atoms of another element.
comet
a ball of dust and ice that orbits the sun
fault
a break in the Earth's crust. It is always younger than the rock it cuts through.
scientific theory
a well tested concept that explains a wide range of observations
Give an example of a good index fossil
ammonite fossils
paleo means
ancient or early
intrusion
beneath the surface magma may push into bodies of rock, the magma cools and hardens there into a mass of igneous rock. This is always younger than the rock layers around and beneath it.
What do both mold and casts preserve
details of the animal or plants structure
What are the basic units of the geologic time scale after the Precambrian time
eras and periods
What 2 processes must take place before unconformity can form
folding and erosion
law of superposition
in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it. Geologists use this method to find a rock's relative age.
Where do radioactive elements occur naturally
in igneous rocks
extrusion
lava that hardens on the surface
continents
less dense rock at Earth's surface formed these large land masses
zoic means
life
atoms
matter is made up of these tiny particles
meso means
middle
What are the most common fossils?
molds and casts
what do fossils do
provide evidence of how life has changed over time, help scientists infer how Earth's surface has changed, are clues to what past environments are like
ceno means
recent
examples of sedimentary rock
sandstone, limestone and coal
paleontologists
scientists who study fossils
What are the 3 eras that geologist divide the time between Precambrian Time and the present into
the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era
What are the 3 periods the Mesozoic Era is divided into
the Triassic Period, the Jurassic Period, and the Cretaceous Period
relative age
the age of a rock compared to other rocks
Evolution
the gradual change in living things over long periods of time
sediment
the material removed by erosion and is made up of rock particles or the remains of living things.
absolute age
the number of years since the rock formed
What clues do scientists use to determine the relative age of rocks?
the position of rock layers, extrusions and intrusions of igneous rock, faults and gaps in the geologic record
fossils
the preserved remains or traces of living things.
unconformity
the surface where new rock layers meet a much older rock surface beneath them. Erosion wears away layers of sedimentary rock.
sedimentary rock
the type of rock that is made of hardened sediment.
petrified means
turned into stone
