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Astrobiology is a scientific field within the life and environmental sciences that studies the origins, early evolution, distribution, and future of life in the universe by investigating its deterministic conditions and contingent events. As a discipline, astrobiology is founded on the premise that life may exist beyond Earth.
The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
Extraterrestrial life, alien life, or colloquially simply aliens is life which does not originate from Earth. No extraterrestrial life has yet been conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more advanced than humanity. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology.
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets.
Nemesis was a hypothetical red dwarf or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU, somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was probably part of a binary system at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago". Such a star would have separated from this binary system over four billion years ago, meaning it could not be responsible for the more recent perceived cycle of mass extinctions.
The Silurians are a race of reptilian humanoids in the long-running British science fiction television series Doctor Who, who first appeared in Doctor Who in the 1970 serial Doctor Who and the Silurians, and were created by Malcolm Hulke. The first Silurians introduced are depicted as prehistoric and scientifically advanced sentient humanoids who predate the dawn of man; in their backstory, the Silurians went into self-induced hibernation to survive what they predicted to be a large atmospheric upheaval caused by the Earth capturing the Moon.
Timeline of paleontology
Extraterrestrial intelligence, or non-human intelligence (NHI), refers to hypothetical intelligent extraterrestrial life. No such life has ever been proven to exist in the Solar System except for humans on Earth, and its existence on other star systems is still speculative. The question of whether other inhabited worlds might exist has been debated since ancient times. The modern form of the concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds. The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture.
In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth required an improbable combination of astrophysical and geological events and circumstances.
The zoo hypothesis speculates on the assumed behavior and existence of technologically advanced extraterrestrial life and the reasons they refrain from contacting Earth. It is one of many theoretical explanations for the Fermi paradox. The hypothesis states that alien life intentionally avoids communication with Earth to allow for natural evolution and sociocultural development, and avoiding interplanetary contamination, similar to people observing animals at a zoo. The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence. A variant on the zoo hypothesis suggested by the former MIT Haystack Observatory scientist John Allen Ball is the "laboratory" hypothesis, in which humanity is being subjected to experiments, with Earth serving as a giant laboratory.
The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
The Silurian is the geological period and system lasting roughly from 445 million years ago to 415 million years ago.
The Ica stones are a collection of andesite stones from the Ica Province in Peru, known for their engraved motifs. Largely regarded to be modern hoaxes, the stones in some cases utilize art styles from various pre-Columbian Peruvian civilizations and often depict anachronistic scenes or objects, including dinosaurs and advanced technology.
The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution.
Plows, Plagues and Petroleum: How Humans Took Control of Climate is a 2005 book published by Princeton University Press and written by William Ruddiman, a paleoclimatologist and Professor Emeritus at the University of Virginia. He has authored and co-authored several books and academic papers on the subject of climate change. Scientists often refer to this period as the "Anthropocene" and define it as the era in which humans first began to alter the Earth's climate and ecosystems. Ruddiman contends that human induced climate change began as a result of the advent of agriculture thousands of years ago and resulted in warmer temperatures that could have possibly averted another ice age; this is the early anthropocene hypothesis.
The cultural impact of extraterrestrial contact is the corpus of changes to terrestrial science, technology, religion, politics, and ecosystems resulting from contact with an extraterrestrial civilization. This concept is closely related to the search for extraterrestrial intelligence (SETI), which attempts to locate intelligent life as opposed to analyzing the implications of contact with that life.
Technosignature or technomarker is any measurable property or effect that provides scientific evidence of past or present technology. Technosignatures are analogous to biosignatures, which signal the presence of life, whether intelligent or not. Some authors prefer to exclude radio transmissions from the definition, but such restrictive usage is not widespread. Jill Tarter has proposed that the search for extraterrestrial intelligence (SETI) be renamed "the search for technosignatures". Various types of technosignatures, such as radiation leakage from megascale astroengineering installations such as Dyson spheres, the light from an extraterrestrial ecumenopolis, or Shkadov thrusters with the power to alter the orbits of stars around the Galactic Center, may be detectable with hypertelescopes. Some examples of technosignatures are described in Paul Davies's 2010 book The Eerie Silence, although the terms "technosignature" and "technomarker" do not appear in the book.
The London Hammer is a name given to a hammer made of iron and wood that was found in London, Texas in 1936. Part of the hammer is embedded in a limey rock concretion, leading to it being regarded by some as an anomalous artifact. The man-made tool is much younger than the Lower Cretaceous rock surrounding it.
Michael R. Rampino is a Geologist and Professor of Biology and Environmental Studies at New York University, known for his scientific contributions on causes of mass extinctions of life. Along with colleagues, he's developed theories about periodic mass extinctions being strongly related to the earth's position in relation to the galaxy. "The solar system and its planets experience cataclysms every time they pass "up" or "down" through the plane of the disk-shaped galaxy." These ~30 million year cyclical breaks are an important factor in evolutionary theory, along with other longer 60-million- and 140-million-year cycles potentially caused by mantle plumes within the planet, opining "The Earth seems to have a pulse," He is also a research consultant at NASA's Goddard Institute for Space Studies (GISS) in New York City.
References
- 1 2 Whitwam, Ryan (April 19, 2018). "Silurian Hypothesis: What If Humans Aren't the First Civilization on Earth?". Extremetech.
- 1 2 3 4 5 Schmidt, Gavin A.; Frank, Adam (2019). "The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?". International Journal of Astrobiology. 18 (2): 142–150. arXiv: 1804.03748 . Bibcode:2019IJAsB..18..142S. doi:10.1017/S1473550418000095. S2CID 55018003.
- ↑ Choi, Charles Q. (April 21, 2018). "Could intelligent life have existed on Earth millions of years before humans?". The Washington Post .
- ↑ "If we weren't the first industrial civilization on Earth, would we ever know?". Technology Review. April 20, 2018.
- ↑ Frank, Adam (2018-04-13). "Was There a Civilization On Earth Before Humans?". The Atlantic .
A look at the available evidence
- ↑ Norton, Andre; Smith, Sherwood (1958). The Time Traders. Tor Books.
- ↑ Niven, L. (February–March 1980). "The Green Marauder". Destinies (short story) – via larryniven.net.