This hypothesis relies on the vast size and consistent physical laws of the observable universe. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking as well as well-regarded thinkers such as Winston Churchill  it would be improbable for life not to exist somewhere other than Earth. Alternatively, life may have formed less frequently, then spread—by meteoroidsfor example—between habitable planets in a process called panspermia.
Examples of glass-like carbon from Gainey, Bay M31, and Topper. Quantities for selected markers are shown in Table 1Evidence of extraterrestrial life abundances of all markers are given in SI Table 4.
Discussion Age of the YDB. Therefore, it appears that the Bay markers are identical to those found elsewhere in the YDB layers that date to Although the Bays have long been proposed as impact features, they have remained controversial, in part because of a perceived absence of ET-related materials.
Although we now report that Bay sediments contain impact-related markers, we cannot yet determine whether any Bays were or were not formed by the YD event.
We investigated whether peaks in YDB markers might be attributed to terrestrial processes. The presence of identical markers found under such a wide range of conditions argues against formation by terrestrial processes and is consistent with an impact origin.
We also examined whether the YDB might represent an interval of reduced deposition, allowing the accretion of interplanetary dust particles enriched in ET markers, such as Ir, Ni, and ET helium.
At Blackwater Draw, based on 24 calibrated 14C dates from Furthermore, abundances of microspherules and magnetic grains decrease with increasing distance from the Great Lakes region see SI Fig. Magnetic Microspherules and Grains.
High concentrations of microspherules glass, clinopyroxene, spinel, or metallic are accepted as evidence for at least 11 older ET impact events Analysis suggests an ET origin, but because of high titanium Ti concentrations, the microspherules differ from typical meteoritic ones.
The magnetic grains and microspherules are anomalously enriched in Ir and Ti see Table 1 and SI Table 5 and are enriched in water up to 28 at.
These ratios and the similarity in composition of YDB magnetic microspherules and magnetic grains e. Some black mats have no algal component, only charcoal. The widespread peaks of charcoal in or near the YDB, and their association with soot and polycyclic aromatic hydrocarbons at specific sites, provide strong evidence for extensive wildfires.
We propose that glass-like carbon, carbon spherules, and nanodiamonds were produced in the YDB by high temperatures resulting from the impact and associated biomass burning. Ir never was detected above or below these layers, lessening concerns about the high uncertainties, while providing strong evidence that Ir concentrations are above background in the YDB or black mat.
The relatively low Ir and Ni peaks associated with the YDB are more consistent with the generally proposed composition of comets and inconsistent with the high-Ir content typical of most stony, nickel—iron, or chondritic meteorites.
Alternately, Ir peaks are found at major geologic boundary layers with no confirmed impacts, and at least some of those Ir concentrations may have resulted from volcanism. However, no major North American volcanic episode is known at Therefore, the high concentrations of Ir do not appear to be of volcanic origin.
We also considered microbial concentration from Ir-rich adjacent sediment, such as occurred in experiments by Dyer et al.
Given the association of high Ir with a suite of other event-related markers, an ET connection is more plausible. Although sample resolution in the ice core was too low to permit us to specifically link the onset of these increased fluxes with the timing of the YD event, the evidence is consistent with the YD event.
As evidence for biomass burning, Mayewski et al. These GISP2 data are consistent with strong geochemical evidence in the GRIP ice core for massive biomass burning at the YD onset, especially a major ammonium spike, in association with peaks in nitrate, nitrite, formate, oxalate, and acetate Altogether, the YD onset was one of the most robust intervals of biomass burning inferred from the Greenland ice cores, although the source of this burning signal must have been far more remote than sources today, because much of the modern forested Arctic region was then covered by ice.
The cause of this biomass burning is consistent with the YD event. Because the heavy minerals, zircon, monazite, and garnet, along with Ti-rich minerals, such as titanite, ilmenite, and rutile, sometimes contain high concentrations of U and Th, we investigated whether lag deposits of those minerals might be the source of high radioactivity.
We conclude that lag deposits may explain the high YDB radioactivity at some sites but not at others. Nature of the Event. The evidence points to an ET event with continent-wide effects, especially biomass burning, but the size, density, and composition of the impactor are poorly understood.
Even so, current data suggest that this impactor was very different from well studied iron, stony, or chondritic impactors e. The evidence is more consistent with an impactor that was carbon-rich, nickel—iron-poor, and therefore, most likely a comet.
Although the current geologic and geochemical evidence is insufficient to fully understand impact dynamics, we can offer speculation for future work.
Although an impactor that size typically leaves an obvious large crater, no such late Pleistocene crater has been identified. The lack of a crater may be due to prior fragmentation of a large impactor, thereby producing multiple airbursts or craters.
Hypervelocity oblique impact experiments P. Thus, lasting evidence may have been limited to enigmatic depressions or disturbances in the Canadian Shield e.Looking for life. Hunting for evidence of alien life is a much trickier proposition than identifying potentially habitable environments.
Just times larger than Earth and orbiting in the habitable zone of a sun-like star, Keplerb could be one of the best place in our galaxy so far to look for extraterrestrial life.
Further investigation will require advanced, space-based telescopes such as those currently in development at NASA. And this painting isn’t alone either, with everything from ancient cave paintings to Sanskrit Scrolls all depicting alien life.
A sighting even crops up in the Bible in The Book of Ezekiel. Either this is compelling evidence, or humanity has a rich tradition of conspiracy theorists.
Catalog of over selected and good-quality UFO cases and reports, including famous and classic cases. Take part in the search for life on tranceformingnlp.com Learn about the Fermi paradox, the search for extraterrestrial intelligence (SETI) and astrobiology.
It's possible that life can only form and thrive on Earth-like planets, which would mean our only chance of detecting aliens is on planets beyond our solar system.