Fossils and Earth's Past

Science

Any method of measuring the age of an object, like tree rings or carbon dating

Absolute dating

Any method of measuring the age of an object, like tree rings or carbon dating. Absolute dating. Absolute dating is a scientific technique used to determine the exact age of an object or event in years.

A thin layer of carbon preserved as a fossil

Carbon film

A thin layer of carbon preserved as a fossil. Carbon film. Carbon film is a type of fossil where the outline of an organism is left behind as a thin layer of carbon residue.

A fossil formed when dissolved minerals fill a mold and harden

Cast

A fossil formed when dissolved minerals fill a mold and harden. Cast. In simple terms, a cast is a replica of an organism made when minerals fill a mold left by the organism.

The largest unit of the geologic time scale, it is divided into eras, periods, and epochs

Eon

The largest unit of the geologic time scale, it is divided into eras, periods, and epochs. Eon is a vast span of geological time lasting hundreds of millions to billions of years.

A unit of geologic time longer than an age but shorter than a period

Epoch

A unit of geologic time longer than an age but shorter than a period. Epoch. An epoch is a time span in Earth's history marked by significant events and changes, like shifts in climate or the development of life forms.

The second-longest unit of geologic time, it is divided into periods

Era

The second-longest unit of geologic time, it is divided into periods. Era. An era is a span of time in Earth's history marked by significant events and changes in the planet's climate and life forms.

The change in a species over time

Evolution

The change in a species over time. Evolution. Evolution is the process by which species adapt to their environment over generations through natural selection.

The death of all members of a species

Extinction

The death of all members of a species. extinction. Extinction is when an entire species completely disappears and no longer exists.

The preserved traces and remains of an organism that lived long ago

Fossil

The preserved traces and remains of an organism that lived long ago. Fossil. A fossil is the remains or impression of a plant or animal that lived millions of years ago, found in rocks.

A timeline of Earth's history based on major changes

Geologic time scale

A timeline of Earth's history based on major changes. Geologic time scale. The geologic time scale is a system of chronological dating that relates geological strata to time, used to understand Earth's history.

The time it takes for half the atoms of a radioactive isotope to decay

Half-life

The time it takes for half the atoms of a radioactive isotope to decay. Half-life. Half-life is the time needed for half of a sample of a radioactive substance to break down into another element.

A fossil from an organism that existed for a short time, it is used to determine the age of other fossils

Index fossil

A fossil from an organism that existed for a short time, it is used to determine the age of other fossils. Index fossil. An index fossil helps scientists determine the age of rock layers.

An atom of the same element with a different number of neutrons

Isotope

An atom of the same element with a different number of neutrons. Isotope. Isotopes are variants of the same chemical element that have differing numbers of neutrons, which can affect the element's stability.

The oldest rock layers are at the bottom and youngest are at the top

Law of superposition

The oldest rock layers are at the bottom and youngest are at the top. Law of superposition. This principle means that in undisturbed rock layers, the deeper you go, the older the rocks are.

A rock fossil created when a buried organism dissolves

Mold

A rock fossil created when a buried organism dissolves. Mold. Mold is a type of fungus that grows in the form of multicellular filaments called hyphae.

A unit of geologic time that lasts tens of millions of years, it is longer than an epoch but shorter than an era

Period

a unit of geologic time that lasts tens of millions of years, it is longer than an epoch but shorter than an era

The breakdown of an unstable atomic nucleus, this releases particles and energy

Radioactive decay

The breakdown of an unstable atomic nucleus, this releases particles and energy. Radioactive decay. It's a process where unstable atoms release energy and particles to become more stable.

Comparing the amount of radioactive and nonradioactive isotopes to determine rock age

Radiometric dating

Comparing the amount of radioactive and nonradioactive isotopes to determine rock age. Radiometric dating is a method used to determine the age of rocks and fossils by measuring the decay of radioactive elements within them.

A method of comparing fossils or rocks to determine which is older

Relative dating

A method of comparing fossils or rocks to determine which is older relative dating. Relative dating is figuring out the age of fossils or rocks based on their position in layers, with deeper layers being older.

A fossil formed in soft sedimentary rock, like a footprint

Trace fossil

A fossil formed in soft sedimentary rock, like a footprint. Trace fossil. A trace fossil is a preserved record of the activity or behavior of ancient organisms, such as footprints, burrows, or feeding marks.

A gap in a rock layer caused by erosion or periods without sediment deposition

Unconformity

A gap in a rock layer caused by erosion or periods without sediment deposition. Unconformity. An unconformity is like a missing page in a history book of Earth's layers due to times when no new layers were added or old ones were worn away.

The theory that geologic processes are the same today as they were in the past

Uniformitarianism

The theory that geologic processes are the same today as they were in the past. Uniformitarianism. It is the idea that the Earth's features are shaped by continuous and consistent processes over time.