The Origin and Evolution of the Earth

Practice flashcards covering the early and modern theories of the origin of the earth and universe, as well as the evolution of the lithosphere, atmosphere, and life.

Nebular Hypothesis

An early argument by Immanuel Kant, revised by Laplace in 1796, suggesting planets formed from a slowly rotating cloud of material associated with a youthful sun.

Otto Schmidt and Carl Weizascar

Scientists in Russia and Germany who revised the nebular hypothesis in 1950, proposing the sun was surrounded by a solar nebula of mostly hydrogen, helium, and dust.

Accretion

The process by which particles in a disk-shaped cloud collided and formed planets, as described in the revised nebular hypothesis.

Big Bang Theory

Also called the expanding universe hypothesis; the most popular modern argument regarding the origin of the universe.

Edwin Hubble

The scientist who, in 1920, provided evidence that the universe is expanding as galaxies move further apart.

Singularity

A "tiny ball" with an unimaginably small volume, infinite temperature, and infinite density that exploded 13.7 billion years before the present to form the universe.

Hoyle’s Concept

The 'steady state' theory which considered the universe to be roughly the same at any point of time.

Galaxy

A structure containing a large number of stars, with diameters ranging from $80,000$ to $150,000$ light years.

Light Year

A measure of distance representing the total distance light travels in one year at a speed of $300,000\,km/second$, equivalent to $9.461 \times 10^{12}\,km$.

Star Formation

A process believed to have occurred some 5-6 billion years ago involving the accumulation of hydrogen gas in a nebula.

Planetesimals

A large number of smaller, rounded bodies developed by cohesion from gas clouds that eventually accrete to form planets.

Differentiation

The process during the earth's formation where materials separated into layers (crust, mantle, and core) based on their densities, with heavier materials like iron sinking to the center.

Solar Winds

Forces that are supposed to have stripped off the primordial atmosphere (hydrogen and helium) from the terrestrial planets.

Degassing

The process through which gases were outpoured from the earth's interior during cooling, starting the evolution of the present atmosphere.

Evolution of Oceans

The accumulation of rainwater in depressions that occurred within 500 million years from the formation of the earth, or about 4,000 million years ago.

Photosynthesis

The process that evolved around 2,500-3,000 million years ago, leading to the saturation of oceans with oxygen and eventually flooding the atmosphere with oxygen 2,000 million years ago.

Origin of Life

A chemical reaction occurring about 3,800 million years ago that generated complex organic molecules capable of duplicating themselves.