Chapter 25: The History of Life on Earth

Earth’s age

Earth formed 4.6 bya

When did life form?

3.4 bya

The Precambrian Era

4 billion years long, 87% of Earth’s history

• First Eon = Hadean Eon

• Second Eon = Archaean Eon

• Third eon = Proterozoic Eon

Hadean Eon

First Eon; formation of solar system, earth, moon and ocean. After Earth formed a rain of asteroids continue to bombard the planet

Archaean Eon

Second Eon; Asteroid bombardment ends, origin of life, volcanos form island arcs in world oceans (no continents yet), origin of photosynthesis - only prokaryotic life exist on Earth

Stromatolites

oldest known fossils, rock-like structures composed of layers of bacteria and sediment that first appeared in the late Archaean Eon

Proterozoic Eon

Third Eon;

• Cyanobacteria proliferate (oxygenate oceans and atmosphere)

• Eukaryotic and multicellular life forms appear

• Sex evolves

• animals evolve

Eukaryotic Red Algae

Organism that evolves sex

Basic steps in evolution of life from non-living matter that occurred in Archean Eon

• Step 1: Synthesis of Org. Compounds on Early Earth

• Step 2: Abiotic Synthesis of Functional Macromolecules

• Step 3: Packaging macromolecules in vesicles

• Step 4: Function of Molecule of Inheritance and the Dawn of Natural Selection

Oparin and Haldane Hypothesis

Early Earth had a reducing atm. with water vapor, methane, and ammonium

• Step 1: Synthesis of Org. Compounds on Early Earth

Miller and Urey Experiments

Took the Oparin-Haldane hypothesis and added an energy source (electricity) and found that it was possible to make formaldehyde, amino acids and other small organic molecules

• Step 1: Synthesis of Org. Compounds on Early Earth

Abiotic Synthesis of Functional Macromolecules

• Small organic molecules polymerize spontaneously when they are concentrated on hot sand, clay, or rock.

• These polymers could then have acted as catalysts for other biological reactions

  • Step 2

Protobionts

aggregates of abiotically produces molecules surrounded by a membrane or membrane-like structure (vesicle) that exhibit simple reproduction and metabolism and maintain and internal chemical environment

• Step 3

Function of Molecule of Inheritance and the Dawn of Natural Selection

RNA molecules called ribozymes have been found to catalyze many different reactions

• Ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA - AUTOCATALYTIC

• A protobiont with ribozymes could grow, split, and pass RNA to its daughters

“Oxygen Revolution”

2.7 bya, O2 began accumulating in the same atm. over a 500 million year period

• Many aerobic prokaryotes perished

• Some survived in anaerobic environments

Origin of O2

produced by oxygenic photosynthesis of cyanobacteria

Oldest Eukaryotic Fossil

Dates to 2.1 BYA

Endosymbiosis

Proposes that mitochondria and chloroplasts were formerly small prokaryotes living within larger host cells

Ancestors of mitochondria and chloroplasts

most likely entered host cell and undigested prey or internal parasites

Endosymbiotic Theory

Key evidence supporting an endosymbiotic origin of mitochondria and plastids:

• Similarities in inner membrane structure/function

• Organelles divide in a process similar to some prokaryotes

• Organelles transcribe and translate their own DNA

• Organelle ribosomes are more similar in size to prokaryotic than eukaryotic ribosomes

When did multicellularity evolve?

Based on DNA “molecular clock” evidence, multicellularity evolved about 1.5 bya

age of oldest multicellular fossil (algae)

1.2 bya

Snowball Earth Hypothesis

Suggests that multicellular organisms remained small until about 565 mya

Ediacaran Fauna

the larger (up to 1 m long), soft-bodied organisms appearing at the time of Snowball Earth

relationship between O2 abundance and collagen

higher oxygen = collagen development

Adaptive values of multicellularity

1. Increased size

   1. Bigger predators can eat a larger range of food; bigger prety can be eaten by fewer organisms

2. Division of Labor

   1. specialization and efficiency

3. Longer lives (cells are replaced)

   1. Life span of organism is not limited to the life span of a particular cell

   2. Longer lifespan means more time for reproduction

Cambrian explosion marks?

Phanerozoic Eon; 565 mya

Cambrian explosion

515 mya, animals diversified into almost all the major groups living today

Cambrian explosion documented fossils

Doushantou (China), Ediacaran (Australia), Burgess Shale (Canada)

Doushantou Microfossils

570-580 mya; researchers identified microfossils (tiny fossils) of sponges, cyanobacteria, multicellular algae, and animal embryos in early stages

Ediacaran Faunas

544-565 mya; in ___, in Australia, paleontologists identified fossils of sponges, jellyfish comb jellies, sea feathers, and traches of other animals.

• These were small, soft-bodied snimals that burrowed in sediments, sat immoble on the seafloor, or floated in the water.

Burgess Shale Faunas

515-525 mya; Virtually every major living group is represented by these fossils from British Columbia, Canada

• Fossils indicate a tremendous increase in the size and morphological complexity of animals, accompanied by diversification in how they made a living.

What triggered the Cambrian Explosion?

1. Increased Oxygen levels

   1. Increased aerobic respiration efficiency

2. Evolution of predation

   1. exerted selection pressure for prey defense strategies

3. New niches beget more new niches

   1. new niches for predators, driving speciation

4. New genes, new bodies

   1. mutations increased the number of HOX genes in animals and made it possible for larger bodies to evolve

HOX Genes

are “homeotic” genes meaning they turn on specific genes

• specifically positional information during development

Homeotic Genes

master regulatory genes that determine the location and organization of body parts

Phanerozoic Eon

Spans the interval between 542 mya and the present. Divided into Paleozoic, Mesozoic and Cenozoic eras.

Paleozoic Era

542-251 mya; Many animal groups, including fungi, land plants, and land animals appeared in the ___ era. This era ends with the obliteration of almost all multicellular life forms at the end of the Permian period

Mesozoic Era

251-65.5 Mya; rise and dominance of dinosaurs and ended with their extinction

Cenozoic Era

65.5 Mya-now; During this time, the mammals diversified after the disappearance of dinosaurs events that occurred today are considered to be part of the ___ era

Mass extinction

Caused by the catastrophic events that eliminate at least 60% of the species within 1 million years

Background extinction

Lower average rate of extinction representing the relatively constant normal loss of some species

Largest mast extinction

End-Permian extinction with 96%

Siberian traps

Flood basalts that added enormous qualities of heat, carbon dioxide and sulfur dioxide to the atmosphere

Impact hypothesis

Hypothesis of Extinction of dinosaurs proposes that an asteroid struck earth 65 million years ago resulting in the extension of an estimated 60-80% of the multicellular species alive

(End-Cretaceous)