Fossils

How old is the Earth?

Approximately 4.5 billion years old

What unit is commonly used to describe deep geological time?

Billions of years (Byrs)

What are the four eons of Earth history?

Hadean, Archean, Proterozoic, Phanerozoic

What does the name Hadean refer to?

Hades; extreme early Earth conditions

What characterizes the Archean eon?

Origin of life and early microbial fossils

What does Proterozoic mean?

“Earlier” or “first” life

What defines the Phanerozoic eon?

“Visible life” with abundant fossils

What is the leading hypothesis for the origin of Earth’s water?

Delivery by asteroids and solar-wind interactions

How did solar wind contribute to Earth’s water?

H⁺ ions reacted with silicate minerals to form OH and H₂O

What asteroid provided evidence for this hypothesis?

Itokawa asteroid

What did scientists find in Itokawa asteroid samples?

Significant amounts of water

What evidence suggests early Earth was a “water world”?

Oxygen isotope ratios in ancient ocean crust

Where was key evidence for a water world found?

Panorama district, Northwestern Australia

What isotope ratio indicates ancient seawater composition?

δ¹⁸O / δ¹⁶O

What does enriched δ¹⁸O suggest about early continents?

Few or no continents were present

When is the earliest evidence of life on Earth?

Approximately 4.1 billion years ago

Where is the earliest evidence of life found?

In the oldest rocks capable of preserving fossils

What form of evidence supports early life at 4.1 Byrs?

Potentially biogenic carbon in zircon crystals

What organisms formed stromatolites?

Cyanobacteria

What are stromatolites?

Layered microbial structures in carbonate sediments

How old are the oldest stromatolites?

Approximately 3.4–3.5 billion years old

What major metabolic process did cyanobacteria invent?

Photosynthesis

What event marks the rise of oxygen in Earth’s atmosphere?

The Great Oxidation Event (GOE)

When did the Great Oxidation Event occur?

Approximately 2.4 billion years ago

What happened to iron during the GOE?

Dissolved iron oxidized and precipitated

What geological feature records this process?

Banded iron formations

What famous iron formation preserves early fossils?

The Gunflint Formation

When did eukaryotes first appear?

Approximately 2.7 billion years ago

When did complex multicellular life emerge?

Approximately 2.1 billion years ago

What was Snowball Earth?

A period of global glaciation

What may have triggered Snowball Earth?

Photosynthesis removed CO₂, reducing greenhouse warming

What gas decreased dramatically during Snowball Earth?

Carbon dioxide

What gas increased prior to Snowball Earth?

Oxygen

What is the Ediacaran Period?

A time of early complex multicellular life

When did the Ediacaran occur?

Approximately 630–542 million years ago

What characterizes Ediacaran organisms?

Soft-bodied, non-predatory forms

Why did Ediacaran organisms lack armor?

Predation had not yet evolved

What is Dickinsonia?

An Ediacaran fossil organism

What is Charnia?

One of the first accepted complex Precambrian organisms

What major evolutionary event followed the Ediacaran?

The Cambrian Explosion

When did the Cambrian Explosion occur?

Approximately 540 million years ago

What defines the Cambrian Explosion?

Rapid evolution of hard body parts and major animal phyla

What famous fossil site documents the Cambrian Explosion?

The Burgess Shale

Name a Cambrian predator

Anomalocaris

Name a bizarre Cambrian organism

Hallucigenia

What early chordate appears in the Cambrian fossil record?

Pikaia

What major evolutionary innovation appeared during the Cambrian?

Hard body parts (weapons and defenses)

Why did hard body parts evolve?

The emergence of predation

What periods follow the Cambrian?

Ordovician, Silurian, Devonian

What characterized the Ordovician period?

Major radiation of marine life

By how much did genera increase during the Ordovician radiation?

Approximately fourfold

Which organisms diversified during the Ordovician?

Brachiopods, bryozoans, cephalopods, crinoids, trilobites

What were Orthocones?

Large straight-shelled cephalopods

Why are Orthocones notable?

They were top predators, not fish

How large could Orthocones grow?

Up to 9 feet long

What were trilobites?

Extinct marine arthropods

What vertebrates existed in the Ordovician?

Small jawless fish

What did early vertebrates lack?

Jaws and bones

What caused the Ordovician–Silurian extinction?

Global cooling and glaciation

When did the Ordovician–Silurian extinction occur?

Approximately 443 million years ago

How severe was the Ordovician–Silurian extinction?

About 60% of marine species went extinct

What tectonic movement contributed to this extinction?

Gondwana moving toward the South Pole