Biology Lecture 2: Earth's History and the Origin of Life

Flashcards covering key vocabulary from the lecture on Earth's formation, geological eras, and the scientific theories behind the origin of life.

Earth's Formation

The creation of Earth approximately 4.6 billion years ago, as part of our solar system's formation from a protoplanetary disk.

Protoplanetary Disk

A massive rotating cloud of dust and gas (hydrogen, helium, and heavier elements from supernovae) from which our solar system, including Earth, formed.

Protoplanets

Clumps of matter that formed due to gravity within the protoplanetary disk, eventually developing into planets.

Four Major Eras of Earth's History

The divisions of Earth's history into the Precambrian, Paleozoic, Mesozoic, and Cenozoic eras, with uneven lengths.

Precambrian

The super eon covering over 85% of Earth's history, divided into the Hadean, Archean, and Proterozoic eons.

Hadean Eon

The earliest part of Earth’s history (beginning 4.6 billion years ago), characterized by a molten planet with no oceans or oxygen, and constant bombardment.

Archean Eon

The eon when Earth’s surface cooled enough for a solid crust and oceans to form, and unicellular life (like stromatolites) appeared around 3.8 billion years ago.

Stromatolites

Layered mats formed by cyanobacteria, representing some of the first known life forms and found as early fossils from the Archean eon.

Cyanobacteria

Among the first known life forms, these unicellular organisms formed stromatolites and are still present today.

Proterozoic Eon

The eon towards the end of which multicellular life first appeared, about 1 billion years ago.

Paleozoic Era

An era (543–250 million years ago) marked by the Cambrian Explosion, the appearance of hard-shelled animals, and the evolution of land plants and vertebrates moving onto land.

Cambrian Explosion

A period within the Paleozoic era characterized by a relatively rapid diversification of animal forms that led to new life filling the oceans.

Permian Extinction (The Great Dying)

The worst extinction event in Earth’s history, ending the Paleozoic era, causing 96% of marine life and 70% of land vertebrates to go extinct.

Mesozoic Era (Age of Reptiles)

An era (250–65 million years ago) during which dinosaurs dominated the land and the first mammals evolved.

K-T Extinction Event

An extinction event about 65 million years ago that ended the Mesozoic era and wiped out non-avian dinosaurs, likely caused by an asteroid impact and/or volcanic activity.

Cenozoic Era (Age of Mammals)

The current era, beginning 65 million years ago, characterized by the dominance of mammals and the emergence of humans.

Panspermia

The hypothesis that life originated elsewhere in the universe and arrived on Earth, possibly via asteroids.

Scientific Definition of Life

For something to be considered alive, it must be organized and able to replicate itself.

Reducing Atmosphere

The early Earth's atmosphere, rich in gases like methane and ammonia but lacking free oxygen, which facilitated the bonding of molecules.

Oxidizing Atmosphere

Earth's modern atmosphere, rich in oxygen, which tends to break molecules apart.

Abiotic Synthesis of Organic Molecules

The natural formation of organic molecules (e.g., amino acids, nucleotides) from non-living matter, without the involvement of life.

Miller-Urey Experiment

A 1953 experiment that simulated early Earth conditions (gases, electrical sparks) and successfully produced essential organic molecules like amino acids.

Building Blocks of Life

Small organic molecules (e.g., amino acids, nucleotides, sugars, lipids, ATP) that are fundamental components for forming larger biological structures.

Polymers

Long chains formed by monomers (small molecules) linking together, crucial for life (e.g., proteins from amino acids, RNA/DNA from nucleotides).

Proximity Problem

The challenge for scattered monomers in the early ocean to come into close enough contact to bond and form polymers.

Protocells

Simple, cell-like structures made from lipids that could trap molecules inside, representing an early step in the organization of life.

Liposome

A hollow spherical bubble formed by a lipid bilayer in water, capable of enclosing molecules, which helps solve the proximity problem.

RNA World Hypothesis

The idea that RNA, rather than DNA, was the first genetic and self-replicating material because of its ability to carry information and perform chemical reactions (as enzymes).

Viroids

Tiny pieces of RNA without a protein coat that infect plants; they are cited as evidence for the RNA world hypothesis due to their organized RNA structure.