the preserved remains or traces of living things
the type of rock that is made of hardened sediment
Fossils in which minerals replace all or part of an organism.
a hollow area in sediment in the shape of an organism or part of an organism
a copy of the shape of the organism that made the mold
An extremely thin coating of carbon on rock.
provide evidence of the activities of ancient organisms.
sticky oil that seeps from earth's surface
hardened resin, or sap of evergreen trees. Insects become trapped and covered with resin; sealing it from air and preserving the insect.
another way in which remains can be preserved
information that paleontologists have gathered about the past life
A well tested concept that explains a wide range of observations
the gradual change in living things over long periods of time
No longer in existence
The age of a rock compared to the ages of other rocks.
The number of years since the rock formed
law of superposition
to determine the relative ages of sedimentary rock layers.
lava that hardens on the surface
The magma cools and hardens into a mass of igneous rock.
breaks in the earth's crust
a gap in the geologic record
a fossil that helps geologists match rock layers
Tiny particles that make up matter
When all the atoms of a particular type of matter are the same, the matter is an element.
Over time, these elements break down, or decay, by releasing particles and energy in a process.
when it first hardens to become a rock
The time it takes for half of the atoms of a radioactive element to decay.
Geologists divide the time between the Precambrian Time and the present into three long units called eras.
animals that do not have backbones
began about 544 million years ago, and last for 300 million years. Ancient life
began about 245 million years ago and lasted about 180 million years. Middle life
began about 65 million years ago and continues to present day. Recent life
eras are subdivided into units of geologic time
geologists further subdivide the periods of the Ceozoic Era
an animal that lives part of its life on land and part of its life in water.
at the end of the paleozoic era many kinds of organisms died out
have scaly skin and lay eggs with tough, leathery shells.
a warm-blooded vertebrate that feeds its young milk