Early Earth & the Origin of Life (Ch. 26)

*The history of living organisms and the history of Earth are inextricably linked:

   Formation and subsequent breakup

of Pangaea affected biotic diversity

 The first photosynthetic organism released oxygen into the air and altered Earth’s atmosphere

Endosymbiotic Theory• certain organelles originated as free-living bacteria

that were taken inside another cell as endosymbionts through endocytosis

Evidence– structural

• mitochondria & chloroplasts resemble bacterial structure• both have double membranes

– genetic• mitochondria & chloroplasts have their own circular DNA,

like bacteria• Mitochondria and chloroplasts have bacteria-like RNA and

ribosomes (70S as opposed to 80S in eukaryote cytoplasms) that enable them to make their own proteins and divide independently of the host cell

– functional• mitochondria & chloroplasts move freely within the cell• mitochondria & chloroplasts reproduce independently

from the cell

Lynn Margulis

• Homo sapiens have changed the land, water, and air on a scale and at a rate unprecedented for a single species

Figure 2. Sea level is changing. Observing stations from around the world report year-to-year changes in sea level. The reports are combined to produce a global average time series. The year 1976 is arbitrarily chosen as zero for display purpose.

Figure 1. Global warming revealed. Air temperature measured at weather stations on continents and sea temperature measured along ship tracks on the oceans are combined to produce a global mean temperature each year. This 150-year time series constitutes the direct, instrumental record of global warming.

History of Life on Earth:  Life on Earth originated between 3.5 and 4.0

billion years ago

  Because of the relatively simple structure of prokaryotes, it is assumed that the earliest organism were prokaryotes

*this is supported by fossil evidence (spherical & filamentous prokaryotes recovered from 3.5 billion year old stromatolites in Australia and Africa)

Layers of blue-green algae

 Major Episodes in the History of Life:

   first prokaryotes- 3.5 to 4.0 billion

years ago

  photosynthetic bacteria- 2.5 billion

years ago

  first eukaryotes- 2 billion years ago 

 

~The oldest unequivocal remains of a diversity of microorganisms occur in the 2.0 BYO Gunflint Chert of the Canadian Shield

~This fauna includes not only bacteria and cyanobacteria but also ammonia consuming Kakabekia and some things that resemble green algae and

fungus-like organisms

  plants evolved from green algae

  fungi and animals arose from different groups of heterotrophic unicellular organisms

   first animals (soft-bodied invertebrates)- 700 million years ago

 

  first terrestrial colonization by plants and

fungi- 475 million years ago

plants transformed the landscape and created new opportunities for all forms of life

Prebiotic Chemical Evolution:   Earth’s ancient environment was

different from today:-very little atmospheric oxygen

-lightning, volcanic activity, meteorite, bombardment, UV radiation all more intense

Oparin / Haldane hypothesis (1920s): the reducing atmosphere and greater UV radiation on primitive Earth favored reactions that built complex organic molecules from simple monomers as building blocks

Miller / Urey experiment (1953):

Simulated atmospheric conditions hypothesized to be on early Earth by constructing an apparatus containing H2O, H2, CH4, and NH3.

Results:• They produced amino acids and other organic

molecules.• Additional follow-up experiments have produced all

20 amino acids, ATP, some sugars, lipids and purine and pyrimidine bases of RNA and DNA.

Origin of Life - Different Hypotheses:

 

*No one knows how life actually began on Earth; experiments indicate key steps that could have occurred.

  Panspermia: some organic compounds may have reached Earth by way of meteorites and comets

meteorite

  Sea floor / Deep-sea vents: hot water and minerals emitted from deep sea vents may have provided energy and chemicals needed for early protobionts

 

  Simpler hereditary systems (self-replicating molecules) may have preceded nucleic acid genes.

  Chemical evolution may have occurred in four stages:

1)   abiotic synthesis of monomers

2)  joining of monomers into polymers (e.g. proteins, nucleic acid)

3)  formation of protobionts (droplets

formed from clusters of molecules)

4)  origin of heredity (likely that RNA was first)

 

Abiotic Synthesis of Polymers

• Researchers have produced amino acid polymers by dripping amino acid solutions onto hot sand, clay, or rock– Form spontaneously without enzymes or

ribosomes

• Polymers are all different (don’t get the same one each time)– May have acted as weak catalysts for reactions

on early Earth???

  Protobionts: collections of abiotically produced molecules (membrane bound) able to maintain an internal environment different from their surroundings and exhibiting some life properties such as metabolism and excitability

(experimental evidence suggests spontaneous formation of Protobionts; some havemembrane potential/excitability)

 

RNA

• RNA can carry out “enzyme-like” functions (ribozymes) – Some can make up short segments of RNA– Some can remove segments of themselves– Some can act on different molecules (tRNA)

• Reactions are slow

possible formation

of protobionts;self-repliating RNA as early

“genes”

The Major Lineages of Life: the old 5 Kingdom System

Living organisms  Prokaryotic Eukaryotic 

Simple/unicells Multicellular

Autotrophic Heterotrophic 

Absorptive Ingestivenutrition nutrition(Animalia) (Fungi)

(Plantae)

(Protista)

(Monera)

How was the atmosphere of the early earth different than it is today?

A. The early earth’s atmosphere contained mostly carbon monoxide

B. The early earth’s atmosphere had more oxygen than it has today

C. The early earth’s atmosphere contained more single celled organisms than it does today

D. The early earth’s atmosphere did not contain oxygen

In the 4-stage hypothesis for the chemical evolution of life,

which of the following is the correct sequence? A. Synthesize monomers; join monomers; form protobionts; system of

heredity

B. Form protobionts; synthesize monomers; join monomers; system of heredity

C. System of heredity; join monomers; synthesize monomers; form protobionts

D. Synthesize monomers; join monomers; system of heredity; form protobionts

What is a protobiont?A. A self-replicating early life form that uses RNA for heredity

B. A group of monomers that join/bond when temporarily bonded to materials such as clay or volcanic rock

C. Early enzymes that were able to join basic amino acids together

D. Collection of abiotically produced molecules that can maintain an internal environment and exhibit some life properties

What is the name of the alternate hypothesis for the “seeding” of organic compounds on earth by meteorites & comets?

A. Deep Sea Vent Hypothesis

B. Panspermia

C. Impact Hypothesis

D. Early Earth “Seeding” Hypothesis

In the old 5 Kingdom system used to classify all life, what are the names of the Kingdoms?

A. Bacteria; Plantae; Animalia; Fungi; Protista

B. Bacteria; Plantae; Animalia; Fungi; Monera

C. Plantae; Animalia; Bacteria; Monera; Protista

D. Plantae; Animalia; Fungi; Monera; Protista