Life may have started soon after Earth became habitable, which leads to thoughts that it could have suddenly arisen in other places in the universe as well.

Named after Frank Drake, the American astronomer who created it in the early 1960s.

Organizes our knowledge and ignorance by separating the number of places where intelligent life exists in our galaxy into a set of terms.

1. The number of stars in the Milky Way that survive sufficiently long for intelligent life to evolve on those planets near them

3. The fraction of those planets that have the necessary conditions for life

4. The probability that life may actually come about on those few planets

5. The chance that the life that does arise may evolve to produce an intelligent civilization. (Meaning a form of life that can communicate with us).

When we multiply these terms together, it should give us our best estimate of the number of planets in the Milky Way that have an intelligent civilization at some point.

To get the number of intelligent civilizations that exist at any given time, we multiply that number by the ratio of the average lifetime of an intelligent civilization and the total lifetime of the Milky Way.

However, based on what we know, there are billions of potential sites for potential life, meaning the potential sites just for any form of life are extremely high.

Example: For thousands of years we believed that we were the center of the universe and everything revolved around us. This made sense at the time as a quick look to the heavens would show that everything seemingly moves around us. This is actually a counterexample as this was the assumption that we are special, when , in this case, we weren't.

Named after Nicolaus Copernicus after he discovered that the Sun was at the center of our solar system and not the Earth.

A quick look at the diversity and origins of various lifeforms on Earth will show that all life comes out of different conditions and varies in physical features greatly.

The theory that comets and other space objects rained upon Earth within the first couple hundred million years of its existence, bringing ice, ammonia, hydrogen cyanide, mineral rich rocks, and many more raw materials for life.

By Stanley Miller and Harold Urey. It was an experiment intended to create a mini-environment similar to that of Earth's when life first originated on Earth.

They discovered that, with as close to past-Earth's conditions as they could possibly create, the water of their environment turned out to be rich in "organic gunk." This meant that it was rich in a compound of numerous complex molecules like sugar and some of the simplest amino acids. It also produced some modestly complex molecules called nucleotides.

Showed that these ancient Earth conditions could produce the necessary starting materials and building blocks for life but there is still a huge gap between these building blocks and full on life. That gap is made up almost entirely of time.

Many view them as potentially the beginnings of life on Earth. They can survive in extreme environments like the sea vents on Earth. If they can survive here, they can survive in unlikely places outside of Earth.

Carbon atoms are imperative to life as they can bond with up to 4 other atoms and when they do, it is a weak bond so it is easier for there to be the mixing of molecules and atoms during the creation of more complex forms of life.

The early arising of life on Earth hints that there is a very real possibility of the spontaneous generation of life, given the necessary conditions

It is actually possible that life has actually been wiped out several times on Earth with the conditions still being right for life to rearise after each one. This is unlikely, but it would mean that life can be reestablished out of "nothing."

More on the sea vents. Around these sea vents appeared to be entirely separate ecosystems totally disconnected from the rest of the world outside of its reliance on the oxygen provided by the undersea plants undergoing photosynthesis.

In all the galaxies, there are likely 10^22 planets. This means that there is an unbelievably large potential for life on other planets.

Several protoplanetary nebular disks in star-forming regions strengthen the idea that planetary systems are actually abundant.

This supports the Big Bang Theory which states that all matter of the universe was at one point in one tiny point of existence. Then, due to some sort of impetus, there was a sort of explosion in which the matter all burst out and occupied space.

This would mean that there was a beginning to the universe and thus, we can more effectively analyze the change of life in the universe over time. We can determine that the conditions of the universe have changed over time, possibly affecting the new arising of life across the universe. Possibly, the conditions for life in the universe were "better" within the first couple hundred million years of the big bang, if it actually occurred.

Recently, NASA’s Kepler satellite provided the first clear evidence of rocky planets. This gives us quite a few candidates for potential life that are inside the habitable zone

The “inside-out” perspective is to study the detailed history of life on Earth over the last 4.6 billion years.

The formation of Earth involved the gathering of rocky materials which came during a period of accumulation and accretion

The Kepler space telescope has greatly expanded the discovery of exoplanets by confirming over 1000 planets and listing another 4000 as candidates.

Should be around 100 years before we can see the surface of planets at the far reaches and beyond our galaxy

For life to develop, certain elements are necessary for sure: carbon, nitrogen, oxygen, phosphorus, and sulfur. These create the backbone of life.

Even with a star, a planet must be within the circumstellar habitable zone: a range of distances within which the radiative output of a parent star allows for liquid water.

Most star systems have rocky inner planets and gaseous outer planets.

A geologically active planet is necessary as they produce plate tectonics which are necessary in the carbon cycle. The convective movement produced by a geologically active planet also produces a magnetic field that shields the planet and any life on it from radiation.

NASA intends to build a telescope called the Terrestrial Planet Finder to search for Earth-like planets

provides a quantitative estimate of the relative probability that complex, macro-organismic life forms could have arisen on other planets outside of Earth.

As of now, only 11 (about 1.7%) of the extrasolar planets known to date have a BCI above that of Europa. However, by extrapolation, that total could be over 100 million in just our galaxy.

ESI (Earth Similarity Index) – relates prospective planets’ conditions to those of Earth.

PHI (Planetary Habitability Index) – provides a second tier of analysis for the search for life.

Many planets have BCIs close to that of Earth, and even Gl 581c is rated above Earth in this regard.

Organic molecules have been found in star forming regions, around protoplanetary disks, in meteorites, in comets, and in deep space

The Hubble Space Telescope has helped scientists discover a massive amount of cosmic turf

Frank Drake estimated 10,000

Carl Sagan estimated around a million technological civilizations in our galaxy alone.

Since 1995, astronomers have detected at least 22 planets orbiting other stars

They have also been found in the rims of Yellowstone springs.