History of Life (ch 17)

What is the name of the timeline scientists use to describe Earth's 4.6-billion-year history?

The Geologic Time Scale (divided into Eons, Eras, Periods).

What are the layered rocks that contain most fossils called?

Sedimentary rocks and their layers are called strata.

Ages of rocks relative to one another can be determined by ______

stratigraphy

In an undisturbed stack of rock layers, where are the oldest fossils found?

At the bottom of the stack, in the deepest layers.

What is used to reconstruct a life’s history?

the fossil record

all organisms of all kinds living at a particular time or place

biota

What are all the plants in a biota called?

flora

What are all animals in a biota called?

fauna

Knowing ______ and ______ allows us to reconstruct what the environment may have been like.

flora, fauna

How do fossils form?

1. the organism needs to be in water or in an area where it can be covered by mud

2. Soft tissues rot, whatever remains is covered in sediment

Why is the fossil record incomplete?

Because fossilization is a very rare event. Most organisms decompose completely after death.

How else can we determine how old something is?

Radiometric dating

______ can be used to determine the actual age of rocks because they decay in a predictable pattern

Radioisotopes

Atoms with the same number of protons and electrons, but different number of neutrons

Isotopes

______ isotopes do not decay overtime

stable

______ decay happens at a constant rate

Isotope

• appearance of a new element

• can be measured

• happens at a constant rate and can be used as a way to measure time passed

decay

What is the "half-life" of a radioactive element?

The time it takes for half of the radioactive material to decay into a stable element.

What's the difference between saying a rock is "older than another rock" and saying it is "65 million years old"?

The first is relative dating (order of events). The second is absolute dating (a specific age).

Why is Carbon-14 dating useless for dinosaur bones?

Dinosaurs died out millions of years ago, but Carbon-14 decays too fast and is only reliable for things under ~60,000 years old.

What method uses Earth's reversing magnetic field, recorded in rocks, as a clock?

Paleomagnetic dating.

cannot be dated accurately and are formed from pre-existing rocks or pieces of once-living organisms

sedimentary rocks

What is the name for the event about 2.5 billion years ago when oxygen from bacteria filled the atmosphere?

The Great Oxidation Event.

What do we call the sudden appearance of most major animal groups in the fossil record about 540 million years ago?

The Cambrian Explosion

What is a "mass extinction"?

A period when a huge percentage of all life on Earth dies out in a short amount of time.

What killed the dinosaurs?

A massive meteorite impact (and its aftermath) about 66 million years ago.

What is the name for the ancient supercontinent that existed about 300 million years ago?

Pangaea.

• Alters habitats

• reroutes ocean currents

• changes weather patterns

• promotes allopatric speciation

• helps explain why fossils in two different regions can be the same

continental drift

How did the movement of continents cause new species to evolve?

It split populations apart, leading to allopatric speciation (evolution in isolation).

What are three ways Earth’s orbit changes?

• major climatic shifts have occurred over periods as short as 5,000 to 10,000 years, primarily as a result of changes in Earth’s orbit around the sun

1. Eccentricity

2. Precession

3. Tilt

The shape of Earth’s orbit around the Sun becomes slightly more and less oval every 100,000 years

Eccentricity

Earth wobbles on its axis as it spins, completing a dull wobble every 23,000 years

Precession

The angle of the Earth’s axis relative to the plane of its orbit changes about three degrees every 41,000 years

Tilt

Besides meteorites, what other natural disaster can cause global climate change and mass extinctions?

Massive volcanic eruptions that release gases and ash into the atmosphere.

How did higher oxygen levels in the past allow for giant insects?

More oxygen could diffuse through their bodies, supporting larger body sizes. Experiments with fruit flies prove this.