Transcript The History of Life on Earth

The History of Life on Earth
Grand Canyon
Earth’s Early History
• How did the Earth form?
– Scientists must explain past events in terms of
processes that they can observe. Charles Lyell
• Why did the Earth form?
– This question is outside of the realm of science.
Earth’s Age
• Over 4,600,000,000 years old.
– First trace of Humans dates to about 1.8 million
years ago.
• More than 99% of all species that have ever
lived have become extinct.
Ohio’s Fossil
The Fossil Record
• Provides evidence about the history of life.
• Shows how organisms have changed over
time.
The Fossil Record
• Radioactive Dating
– Calculate age of sample based on amount of
remaining radioactive isotope it contains based on
the isotopes half-life.
• Relative Dating
– The age of a fossil is determined by comparing its
placement with that of fossils in other layers of
rock.
Earth’s Early Atmosphere
Earth’s Early Atmosphere
• Probably contained hydrogen cyanide, carbon
dioxide, carbon monoxide, nitrogen, hydrogen
sulfide, and water.
– If you were to travel back in time, after a few short
breaths you would no longer exist.
Earth’s Atmosphere
• Earth was formed 4.6 billion years ago.
• Around 3.8 billion years ago changes occurred
in Earth’s atmosphere.
• Water could remain a liquid on the planet.
Earth’s Atmosphere
Earth’s Atmosphere
• First life found to be around 3.5 billion years
old. What type of life?
– Single-celled prokaryotic ancestors of modern
bacteria.
• Little to no oxygen present in Earth’s
atmosphere. How is this possible?
– Chemosynthesis.
Earth’s Atmosphere
• 2.2 Billion Years ago
• Organisms began producing oxygen, an end
product of?
• How could this be?
– Observation of Oxygen reaction with iron and
water. Many rust deposits in rocks dated to this
time.
Rusty Rocks
Earth’s Atmosphere
• Organisms churning out Oxygen
• What would this do to the atmosphere?
– Oxygen increase, methane and hydrogen sulfide
concentrations decreased.
• What would this do to the microbes on Earth?
• Remember we are talking about BILLIONS of
years!!
The Increase in Oxygen
• Poisonous, reactive gas.
• Peace early life forms.
• Hello life forms equipped to use oxygen in
their metabolic pathways.
– Respiration
The Increase in Oxygen
• Stage set for the gradual transition to
“modern” life and the gradual transition to
modern atmosphere.
– Oxygen increase in the atmosphere took over
HALF A BILLION YEARS!
– Descendants of early anaerobic life forms still exist
today.
– Use other chemicals such as nitrates and sulfates
for metabolism.
Origin of Eukaryotic Cells
Origin of Eukaryotic Cells
• 2 billion years ago.
• Internal cell membranes began developing in
prokaryotes.
• Ancestral eukaryote engulfed prokaryotes.
Origin of Eukaryotic Cells
• Endosymbiotic theory
– Eukaryotes engulfed and formed a symbiotic
relationship with prokaryotic organisms. Engulfed
prokaryotes are modern day chloroplasts and
mitochondria.
– Mitochondria and Chloroplasts share many
similarities with free-living bacteria.
Origin of Eukaryotic Cells
Geologic Time Scale
Geologic Time Scale
Geologic Time Scale
Geologic Time Scale
Macroevolution
• Macro?
– Big
• Evolution?
– Change over time.
• Macroevolution
– Large scale evolutionary changes that take place
over a long period of time.