Extraterrestrial Life: From Ancient Times to Today

Posted on Mar 16, 2025 in Physics

The Possibility of Extraterrestrial Life

The possibility of extraterrestrial life was first considered during ancient times.

In science, conceptual representations of observed phenomena are referred to as models.

The circular shape of the Earth’s shadow on the Moon during a lunar eclipse suggested to the Greeks that the Earth was spherical in shape.
The Ptolemaic model has planets moving in small circles.
The first person to suggest that the Earth moved around the Sun was Aristarchus.
Which Greek school of thought believed that both the heavens and the Earth were made of an infinite number of indivisible units made of the elements fire, water, earth, and air? Atomists.

Kepler’s 1st Law of planetary motion states that the orbits of the planets are ellipses with the Sun at one focus.
In its elliptical orbit, a planet is closest to the Sun at perihelion.
Kepler’s 2nd Law of planetary motion states that an imaginary line joining the Sun and planet sweeps out equal areas in equal times.
In its elliptical orbit, a planet is furthest the Sun at aphelion.
Kepler’s 3rd Law of planetary motion states that the further a planet is from the Sun, the slower it moves in its orbit.

Hypothesis: An educated guess.
Occam’s Razor: Choose the simplest explanation.
A scientific model is considered valid if it is consistent with independent observations by other scientists.

Which of the following places the structures in our own part of the universe in order of increasing (smallest to largest) scale?: Solar System – Milky Way (about one hundred billion stars), Local Group, Local Supercluster.
Most of the mass of the Milky Way is in the form of dark matter.
The universe is made of dark energy.
Evidence for the Big Bang theory: leftover radiation.
The expansion of the universe has been speeding up.
A star that is more massive than the Sun will have a shorter lifetime because it’s hotter.

In our solar system, Terrestrial planets are: small, made mostly of rock and iron with high densities, and found close to the Sun.
Human beings mostly emit which kind of electromagnetic radiation?: Infrared
Which of the following sequence of electromagnetic radiations is in order of increasing frequency?: Radio, infrared, UV, gamma ray
Which of the following sequence of electromagnetic radiations is in order of increasing wavelength?: X-ray, visible, infrared, radio.

Which of the following do the atoms ¹⁴N and ¹⁵N have in common? Number of protons.
Which of the following do the atoms ¹⁴C and ¹⁴N have in common? Total number of protons and neutrons.
How many electrons are present in the ion of the isotope of cobalt, 60Co2+ if cobalt has an atomic number of 27? 25.
Compared to its neutral atom, an ion has the same number of protons but a different number of electrons.
How many neutrons are in an isotope of uranium-235 if uranium has an atomic mass number of 92? 143
An isotope of the element Manganese (Mn) has an atomic number of 25 and a mass number of 55. Assuming the atom is neutral, this means it has 25 protons, 25 electrons, and 30 neutrons.
Asteroids and comets are planetesimals left over from the era of planet formation.
The carbon dioxide cycle is an example of a negative feedback process
At the beginning of which eon of Earth’s history did life originate? Archean.