Earth has been habitable for 4.3 billion years, and the earliest rock record indicates the
presence of a microbial biosphere by at least 3.4 billion years ago—and disputably earlier …

Abstract The Archean era (4 to 2.5 billion years ago, Ga) yielded rocks that include the
oldest conclusive traces of life as well as many controversial occurrences. Carbonaceous …

The search for traces of life is one of the principal objectives of Mars exploration. Central to
this objective is the concept of habitability, the set of conditions that allows the appearance …

While grounded in the hard sciences of physics, chemistry, geology, and astronomy, as well
as well-accepted principles in the life sciences, astrobiology remains the most speculative of …

Microbial life permeates Earth's critical zone and has likely inhabited nearly all our planet's
surface and near subsurface since before the beginning of the sedimentary rock record …

Life requires a wide variety of bioessential trace elements to act as structural components
and reactive centers in metalloenzymes. These requirements differ between organisms and …

Fungi have recently been found to comprise a significant part of the deep biosphere in
oceanic sediments and crustal rocks. Fossils occupying fractures and pores in Phanerozoic …

It is often acknowledged that the search for life on Mars might produce false positive results,
particularly via the detection of objects, patterns or substances that resemble the products of …

Here we review published studies on the abundance and diversity of terrestrial rock-hosted
life, the environments it inhabits, the evolution of its metabolisms, and its fossil biomarkers to …

The search for life beyond Earth has focused on Mars and the icy moons Europa and
Enceladus, all of which are considered a safe haven for life due to evidence of current or …