Origin of Life

ASTR 4: Life in the Universe

Outline

• Fossil Records Reconstruction• Evolution• Tree of Life• Eukaryote Evolution• Lateral Gene Transfer• Theories of Origin of Life• Required Steps• Global Catastrophes

Fossil Formation• fossils are more difficult to find as we look back to earlier epochs

• more organisms which lacked skeletons leave fewer fossils

• erosion erases much old fossil evidence

• subduction destroys fossils carries deep beneath Earth’s surface

• we have found fossils of large & small animals, plants, microorganisms

• the fossil record goes back 3.5 billion years• deficit of 13C, a sign of life, in rocks as old as 3.85 billion years

Fossil Records

Fossil Records

Radiometric dating shows that some stromatolites are 3.5 billion years old.

Fossil Records

This microscopic photo shows a chain of modern cyanobacteria. The ancestors of these living organ- isms produced essentially all the oxygen in Earth’s atmosphere.

Evolution

• Biological Evolution– Jean Baptiste Lamarck (1800s)– The relationship between fossils and living organisms

is that life-forms evolve by gradually adapting to perform successfully in their environments.

• Darwin’s Explanation: Unequal Reproductive Success (Natural Selection)– Overproduction and struggle for survival– Individual variation

Armand Delsemme. Our Cosmic Origins. Canbridge University Press.

Armand Delsemme. Our Cosmic Origins. Canbridge University Press.

Eukaryote Evolution

• At Least Two Stages– Enfolding: Formation of nucleus– Endosymbiotic Hypothesis First eukaryote was a

symbiotic relationship of different prokaryotes

Prokaryote-Vs-Eukaryote

Endosymbiotic Hypothesis • Proposed by Lynn Margulis, Boston U.• Margulis L (1970) Origin of Eukaryotic

Cell, Vol. Yale University, New Haven, CT.

First mitochondria or chloroplast

Progenote

Archaea

Cytoplasm

Urcaryote

Eucarya

Protozoa

PlantsFungi

Animals

Chloroplasts

Cyanobacteria

-proteobacteria

Bacteria

Mitochondria

Endosymbiotic Hypothesis

Evidences

• Much basic biochemistry [e.g. Kreb’s cycle (ATP ADP) and genetic code] is the same for prokaryotes and eukaryotes

• Organelles (e.g. mitochondria) have double-layer membranes

• Organelles have some DNA and organelle specific genes, divide somewhat independently of entire cell

Effect of Lateral Gene Transfer

Required Steps

Armand Delsemme. Our Cosmic Origins. Canbridge University Press.

Miller-Urey Experiment in 1953 at the University of

Chicago

These microscopic photos show enclosed membranes that self-assemble in laboratory experiments mimicking conditions on the early Earth. (Left) These microscopic spheres were made by cooling a warm water solution of amino acids. They are not alive, but they exhibit many life-like properties. (Right) These microscopic membranes are made from lipids that, when mixed with water, spontaneously form enclosed droplets.

Mass Extinction

Mass Extinction

Mass Extinction

Mass Extinction

The arrow points to a layer of sediment laid down on Earth by an impact 65 million years ago, which is linked to the extinction of the dinosaurs. The sediment is about 2 centimeters thick at this location.

Mass Extinction

This computer-generated image, based on measurements of small local variations in the strength of gravity, shows an impact crater in the northwest corner of Mexico’s Yucatán peninsula. The crater measures about 200 kilometers across, and about half of it lies underwater off the coast. The red box on the inset map shows the region covered by the image. The white lines on the image show the coastline and the borders of Mexican states.

Mass Extinction

A PLOT OF DATA ON LIFE EXTINCTIONS, COLLECTED BY DAVID RAUP AND JOHN SEPKOSKI AT THE UNIVERSITY OF CHICAGO, SHOWS PEAKS IN THE EXTINCTION RATE OCCURRING AT 26- TO 30-MILLION-YEAR INTERVALS, AS INDICATED BY ARROWS