12.1 The Fossil Record KEY CONCEPT Specific environmental conditions are necessary in order for...

12.1 The Fossil Record

KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.


Fossils can form in several ways.

• Permineralization occurs when minerals carried by water are deposited around a hard structure.


• A natural cast forms when flowing water removes all of the original tissue, leaving an impression.


• Trace fossils record the activity of an organism.


• Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.


• Preserved remains form when an entire organism becomes encased in material such as ice.


• Specific conditions are needed for fossilization.• Only a tiny percentage of living things became fossils.


Radiometric dating provides an accurate way to estimate the age of fossils.

• Relative dating estimates the time during which an organism lived.– It compares the placement

of fossils in layers of rock.– Scientists infer the order in

which species existed.


• Radiometric dating uses decay of unstable isotopes.

– Isotopes are atoms of an element that differ in their number of neutrons.

neutrons protrons


– A half-life is the amount of time it takes for half of the isotope to decay.

• Radiometric dating uses decay of unstable isotopes.

– Isotopes are atoms of an element that differ in their number of neutrons.


KEY CONCEPT 12.3The origin of life on Earth remains a puzzle.


Earth was very different billions of years ago.

• There have been many hypotheses of Earth’s origins.• The most widely accepted hypothesis of Earth’s origins is

the nebula hypothesis.


Several sets of hypotheses propose how life began on Earth.

• There are two organic molecule hypotheses.– Miller-Urey experiment

– meteorite hypothesis

electrodes

heat source amino acids

water

“atmosphere”

“ocean”


• There are different hypotheses of early cell structure.

– iron-sulfide bubbles hypothesis


• There are different hypotheses of early cell structure.– lipid membrane hypothesis


• A hypothesis proposes that RNA was the first genetic material.

– Ribozymes are RNA molecules that catalyze their own replication.

– DNA needs enzymes to replicate itself.

12.1 The Fossil Record KEY CONCEPT Specific environmental conditions are necessary in order for...

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