Earth and Space Quiz #1 Study Guide - Flashcards (Geologic Time & Fossils)

Study flashcards covering geologic time units, Earth's early history, and fossil concepts based on lecture notes.

How old is the Earth?

Approximately 4.56 billion years.

What were the initial conditions on Earth when it first formed?

Very hot with lava, cooling over time, mostly volcanic activity, and little to no oxygen.

Which organisms contributed to the rise of oxygen in Earth's atmosphere?

Photosynthesizing stromatolites (early cyanobacteria).

What is the general progression of Earth’s early history from formation to today?

Cooling lava and volcanic activity → rise of oxygen from stromatolites → appearance of water → life (dinosaurs) → extinction events → today.

List the geologic time units from largest to smallest.

Eons, Eras, Periods, Epochs.

Which geologic time unit is the largest?

Eons.

Which geologic time unit is the smallest?

Epochs.

Why do boundaries between geologic periods begin?

Because of major changes in life forms (biological evolution).

What percent of geologic time does the Precambrian Eon occupy?

About 88%.

What is a fossil?

Remains or traces of prehistoric life preserved in rock.

What conditions are important for fossil formation?

Rapid burial and hard parts to preserve the remains.

What is the difference between unaltered and altered fossils?

Unaltered fossils are preserved with little change; altered fossils have changed over time.

What is a mold fossil?

An impression left in sediment (the outline of the organism, like a cookie cutter).

What is a cast fossil?

A replica formed when sediment fills a mold.

What is a trace fossil?

Evidence of an organism’s activity, such as footprints or feces (coprolites).

What is fossil succession and how is it used to date rock layers?

Lower rock layers are older and higher layers are younger; used to establish relative ages of rocks.

What is an index fossil and what criteria define it?

A fossil that is widely distributed, existed for a relatively short time, and is abundant; used to date rock layers.