Transcript PPt - My eCoach

UNIT 12: GEOLOGIC TIME
12.1 KEY CONCEPT
Fossils can help us understand how organisms have
changed over time, and the time frame in which they
existed.
FORMATION OF FOSSILS
• Specific conditions are needed for fossilization.
• Only a tiny percentage of living things became fossils.
RADIOMETRIC DATING OF FOSSILS
Radiometric dating provides an accurate way to estimate
the age of fossils.
• It estimates the time during which an organism lived.
• It compares the placement
of fossils in layers of rock.
- Older species are lower in
the layers.)
- More recent species are in
higher layers)
THE GEOLOGIC TIME SCALE
12.2 KEY CONCEPT
The geologic time scale divides Earth’s history based
on major past events.
The geologic time scale organizes Earth’s history.
• The history of Earth is
represented in the geologic time
scale.
100
250
550
1000
2000
PRECAMBRIAN TIME
This time span makes up the
vast majority of Earth’s history.
It includes the oldest known
rocks and fossils, the origin of
eukaryotes, and the oldest
animal fossils.
Cyanobacteria
12.3 KEY CONCEPT
The origin of life on Earth remains a puzzle.
THE FORMATION OF EARTH
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.
ORIGINS OF LIFE ON EARTH
Several sets of hypotheses propose how life began on
Earth.
• There are two organic molecule hypotheses.
– Miller-Urey experiment
electrodes
“atmosphere”
water
“ocean”
heat source
– meteorite hypothesis
amino acids
ORIGINS OF LIFE ON EARTH
Miller & Urey’s Evidence
• Miller & Urey show that if a “soup” of inorganic
compounds is zapped with electricity, ORGANIC
molecules can form.
• (Organic molecules are the ones that living things are
made of.)
• So, simple life may have begun if the right combination of
chemicals was exposed to, say, lightning (electricity.)
12.4 KEY CONCEPT
Single-celled organisms existed 3.8 billion years ago.
Microbes have changed the physical and chemical
composition of Earth.
• The oldest known fossils are a group of marine
cyanobacteria.
– prokaryotic cells
– added oxygen to
atmosphere
– This allowed animals
to develop
12.5 KEY CONCEPT
Multicellular life evolved in distinct phases.
The Paleozoic Era
• Multicellular organisms first appeared during this era.
• It began 544 million years ago
• Life moved onto land in the middle of this era
• It led to a huge diversity of animal species.
The Mesozoic Era
• The Mesozoic era is known as the Age of Reptiles.
• It began 248 million years ago
• Dinosaurs, birds, flowering plants, and first mammals
appeared.
The Cenozoic Era
Mammals radiated during the Cenozoic era.
• This era began 65 million years ago and continues today.
• Placental mammals evolved and diversified.
• modern humans appeared late in the era.
12.6 KEY CONCEPT
Humans appeared late in Earth’s history.
Humans share a common ancestor with other primates.
• Primates are mammals with flexible hands and feet,
forward-looking eyes and enlarged brains.
Hominids & their close “relatives”
– Hominids include
living and extinct
humans.
– The Homo genus
first evolved 2.4
million years ago.
Characteristics of Hominids
• Bipedal means walking on two legs.
– foraging
– carrying infants and food
– using tools
• Walking upright has
important adaptive
advantages.
Characteristics of Hominids
Modern humans arose about 200,000 years ago.
• Homo sapiens (modern human) fossils date to 200,000
years ago.
• Human evolution is influenced by a tool-based culture.
• There is a trend toward increased brain size in hominids.
Australopithecus
afarensis
Homo habilis
Homo
neanderthalensis
Homo sapiens