Which explains why oxygen was absent from Earth's early atmosphere?

Which gas most likely was not part of Earth's early atmosphere?

What is the name of the first eon in Earth's history?

During which time period of Earth's history did mammals become more abundant on land?

Which time period did dinosaurs first emerge in?

Preserved the body parts of a mosquito in tree sap is called what type of fossil?

Created an impression of an extinct trilobite.

Preserved a line formed in wet sand by a dinosaur dragging its tail.

A tree trunk that has slowly been filled in with minerals such as calcium, petrifying the wood.

Which of the following best describes the Paleozoic era?

Which era does the Earth form and the first life forms appear?

Mammals appear in which period?

Humans appear during which period?

A scientist who travels to Argentina to explore a field of newly discovered dinosaur bones is called ___________.

A one million-year-old layer of sandstone lying on top of a 1.5 million-year-old layer of granite is an example of the _________________.

The model that expresses the major geological and biological events during Earth's history is called the ____________.

What geologic time period are we currently in?

Which describes what scientists think the conditions of Earth were like 4.5 billion years ago?

Which was the original source of atmospheric oxygen?

Which fossil will reveal the skin color of a 90 million year old frog?

A mass extinction that included the disappearance of dinosaur species occurred during which period?

Most scientists agree that...

What are radioactive isotopes?

Preserved evidence of an organism is called ________.

The use of radioactive potassium-40 to date a granite rock fragment is called _______.

Eras are divided into lengths of time called _________.

The theory that the continents are drifting on large plates across Earth's surface is called ____________.

Where did the gases that make up the atmosphere most likely come from?