A fossil site has early dinosaurs dated about 230 Ma. Using the era boundaries on the timeline, in which era does 230 Ma fall?

A rock layer with early shelled organisms is dated about 520 Ma. Which period contains that age?

A plant fossil horizon is dated about 430 Ma. Which Paleozoic period contains that age?

A fossil of an early amphibian is found in rocks dated about 370 Ma. Which period should be assigned to that fossil?

Coal-forming swamp deposits are dated about 310 Ma. Which period on the time scale contains that age?

The earliest definitive dinosaur fossils are about 230 Ma. Which Mesozoic period contains that age?

A dinosaur trackway is dated to 170 Ma. Which period contains the trackway?

Early flowering plant fossils are placed at about 130 Ma. Which period contains that event?

Early primates appear on a timeline shortly after 66 Ma, around 60 Ma. Which Cenozoic period contains that age?

A grassland expansion is dated to 10 Ma. Which Cenozoic period contains that age?

Modern humans appear in the rock and fossil record during the late Cenozoic. Which period contains that event?

Early bacteria and algae are shown about 3500 Ma on a classroom time scale. Which eon contains that age?

Use the timeline. The long blank span from about 4600 Ma to 538.8 Ma comes before the Phanerozoic. What is that span called?

On the timeline, the blank interval runs from about 538.8 Ma to 252.2 Ma. Which era belongs in the blank?

The blank interval on the timeline begins at 252.2 Ma and ends at 66 Ma. What era is missing?

A timeline has a blank era from 66 Ma to the present. Which label completes that interval?

In the Paleozoic part of the timeline, the blank period begins at 538.8 Ma and ends near 486.9 Ma. What is it?

On the timeline, a blank period lies between the Cambrian and the Silurian. Which period is missing?

A blank Paleozoic period starts near 419.2 Ma and ends near 358.9 Ma. Which period should label it?

The blank period on the Mesozoic timeline is between the Triassic and the Cretaceous. What label belongs there?

A Cenozoic timeline leaves the period from 23 Ma to 2.58 Ma blank. Which period is it?

The youngest blank period on the timeline starts at 2.58 Ma and reaches the present. What is it called?

A blank eon begins near 2500 Ma and ends at the start of the Phanerozoic. Which eon is missing?

Order these from oldest to youngest: first dinosaurs, early bacteria and algae, modern humans, first land plants.

Put these boundaries in order from oldest to youngest: start of Cenozoic, present, start of Paleozoic, start of Mesozoic.

Order these Paleozoic events from oldest to youngest: first forests, early shelled organisms, coal-forming swamps, primitive fish.

Arrange the Mesozoic periods from oldest to youngest.

Order the Cenozoic periods from oldest to youngest.

Place these from oldest to youngest: Proterozoic, Hadean, Phanerozoic, Archean.

From oldest to youngest, order these events: complex multicellular organisms, first dinosaurs, Earth forms, early bacteria and algae.

Put these extinction events from oldest to youngest: end Triassic, end Ordovician, end Cretaceous, end Permian.

Sort these from oldest to youngest: first dinosaurs, early primates, first amphibians, first reptiles.

Order these intervals from longest ago to most recent: Jurassic, Quaternary, Cambrian, Permian.

A teacher lists epoch, eon, era, and period. Which rank is the largest division of geologic time in that list?

The Jurassic is one division of the Mesozoic Era. What rank is the Jurassic?

The Cenozoic is one division of the Phanerozoic Eon. What rank is the Cenozoic?

The Holocene is a division within the Quaternary Period. What rank is the Holocene?

In the hierarchy eon → era → period → epoch, what rank comes immediately below era?

The Cambrian, Ordovician, and Silurian are all periods of geologic time. In which era do all three fall?

At 66 Ma, the timeline marks the end of the Cretaceous and the start of the Cenozoic. What major event defines that boundary?

The Paleozoic-Mesozoic boundary is drawn at 252.2 Ma. Which event is used to mark that boundary?

The boundary between the Triassic and Jurassic is at about 201.3 Ma. Which event is shown there on many geologic timelines?

At about 443 Ma, the Ordovician ends and the Silurian begins. Which boundary event fits that horizon?

Near 538.8 Ma, abundant complex animal fossils become common in the rock record. Which boundary is this?

A rock layer contains evidence of the Chicxulub impact and many disappearing species. Which boundary does it most likely record?

Why do many named boundaries on the geologic time scale line up with abrupt fossil changes?

Earth is about 4600 million years old, and the Cenozoic began about 66 million years ago. About what share of Earth history is the Cenozoic?

The Phanerozoic covers about 538.8 million years of Earth's 4600 million years. Rounded to the nearest percent, what share is that?

Precambrian time lasted from about 4600 Ma to 538.8 Ma. About what percent of Earth's history was Precambrian time?

The Mesozoic lasted from about 251.9 Ma to 66 Ma. Compared with Earth's 4600 million years, about what percent of Earth history is that?