Chapter 17 pg. 439

The exact origins of life are unclear

We will examine the most plausible explanations and theories.

Main Ideas: Evolution and the Origins of Life

Space programs & imaging Crust Deposits Computer Simulations Fossilized Remains & DNA analysis

Evidence used to determine origins.

Hubble’s theory of an expanding universe

Redshift and Blueshift Similar to the doppler effect in sound waves.

15 billion years ago the universe was more concentrated & exploded sending matter and energy into space

Gravity caused the matter to clump together into planets and galaxies.

Section 1: The Big Bang

Earth’s molten core suggests that Earth began as a hot mass that lost heat from its surface creating the surrounding atmosphere of gases

The atmosphere likely arose from volcanic eruptions and played a role in the origins of living organisms. (still debated )

Geologic evidence does not support the presence of O2 in the early atmosphere. ◦ But Why?

Section 2: Early Earth

Oxygen was trapped in compounds (water & carbon dioxide)

Accumulated after early photosynthetic organisms began to produce it

Atmosphere was rich in nitrogen and carbon dioxide

Extreme UV radiation from the Sun created a hostile environment on Earth

The now protective Ozone layer did not arise until photosynthetic organisms added O2 to the atmosphere over millions of years. ◦ Ultraviolent radiation converts O2 into O3

Section 3: The Beginnings of Life

1. Life originated on some planet of another star and traveled to Earth through space on a bicycle. (ET)

2. Life originated by unknown means of Earth

3. Life evolved from nonliving substances through interaction with the environment.

Scientific Explanations for life in a chaotic environment:

What makes a hypothesis testable?

Could we design an experiment to test or investigate these 3 explanations?

*Let’s examine some hypotheses and determine their testability*

Science concentrates on investigating the most testable hypotheses, not necessarily the most interesting or likely alternatives

Design an experiment to answer a question you have about the natural world

◦Design needs to include: The question being investigated Your hypothesis (“if then statement”) Procedures (how would you test it) Variables Data Collection ( how would you collect

data)

Experimental Design Assignment Due Monday 8/10

Life evolved from nonliving substances by interacting with the natural environment.

Oparin & Haldane: Energy sources caused atmosphere gases to react and form organic compounds. Accumulation = “Hot Soup”

Chemical Evolution (Fig. 17.8)

Section 4: Chemical Evolution

Chemical reactions continued and transformations occurred leading to more organic molecules

Both Oparin and Haldane suggested the first life forms were heterotrophic organisms that survived consuming organic compounds

3 major steps

There had to be a supply of organic molecules produced by nonbiological processes

Processes had to polymerize molecules into Nucleic Acids & Proteins

Other processes had to organize the polymers into a system that could replicate itself using the organic materials produced in step 1.

Heterotroph Hypothesis

Synthesized organic compounds using electricity & chambered apparatus to recreate Earth’s early atmosphere.

Results:◦Small mass of black tar ◦Water Turned Red (accumulation of

unidentifiable compounds)◦Combination of gas molecules forming new

complex molecules

Miller & Urey ( review Bio 1)

The liquid contained amino acids

Amino acids are essential for all living organisms

It was possible cosmic energy reacted with the gases in Earth’s early atmosphere to create organic molecules essential to life

Conclusion from Miller & Urey

Examination of meteorite 1969 –found 2 amino acids that do not occur in living organisms on earth.

Halley’s Comet 1986- contained several organic compounds including Formaldehyde

Other Evidence of organic compounds in space

b

Replication of the system

DNA molecules are the universal information molecule. DNA replication requires proteins. Protein structure is coded in DNA.

SO which came first? Protein or DNA

The Chicken & the Egg

The components of RNA can be produced nonbiologically◦ Ribose, nitrogen, phosphate

The components can join spontaneously

Some RNA molecules can catalyze their own partial replication

This evidence supports the theory that early polymers could organize into systems with the ability to replicate themselves using organic molecules.

RNA!

Scientists have not yet found RNA molecules that can replicate themselves completely

Laboratories have been able to simulate Darwinian evolution with RNA molecules that catalyze specific reactions.

The catch…

RNA serves as the catalyst in a chemical reaction in some single-celled eukaryotes

RNA molecules that act as enzymes are called Ribozymes

Ribozymes can catalyze changes in other molecules or act on themselves.

Ribozymes that act on themselves are not considered true catalysts because they are changed as a result of the reaction.

Catalytic RNA

The ability of the RNA molecule to act as a catalyst depends on its three-dimensional structure

A double-stranded region at least 3 base pairs long is needed to stabilize the loops that give the ribozyme its catalytic structure

Be sure to examine Fig. 17.15

According to NASA’s Exobiology Program Life = a self-sustained chemical system that is capable of undergoing Darwinian, or biological, evolution

17.5: Biological Evolution

Biological Evolution consists of 3 processes◦Self-reproduction◦Mutation that can be inherited ◦Natural Selection

Example organism that undergo these processes include◦Humans, bacteria, lizards◦Basically all living organisms on the Earth

The oldest know microfossils are of tiny, single-celled filaments◦ Found in northwestern Australia

The discovery of these microfossils provide evidence that life appeared on Earth much early than previously thought. ◦ Found in rocks formed almost 3.5 billion years ago

17.6 : Microfossils & Prokaryotes

Carl Woese suggests that the first microorganisms were methanogens which are anaerobic bacteria that obtain energy by using carbon dioxide to oxidize hydrogen.

Methanogens live in extreme conditions thought to be like those of the early earth (extremophiles)

They can live near hydrothermal volcanic vents(hot) or rock wastes from mining (acidic)

The first microfossils determined to be eukaryotic are around 2.1 billion years old.

Fossil evidence indicates eukaryotes thrived around750 million years ago

Endosymbiotic theory: eukaryotes evolved from the symbiotic relationships among various prokaryotic organisms

Lynn Margulis hypothesized that mitochondria and plastids originated as free-living prokaryotes

17.7 Eukaryotes

Symbiotic relationships among the prokaryotes may have provided those organisms with an environmental advantage compared to the prokaryotes lacking the symbiotic abilities.

Internal partners are called endosymbionts.

Endosymbiosis

LO 1.27 Student is able to describe a scientific hypothesis about the origin of life on Earth

LO 1.28 Student is able to evaluate scientific questions based on the hypotheses about the origin of life on Earth

LO 1.29 Student is able to describe reasons for revisions of scientific hypotheses of the origin of life on Earth

LO 1.32 Student is able to justify the selection of geological, physical, and chemical data that reveal early Earth conditions.

Learning Objectives