Meteorites Meteorites are solid objects originating in outer space that survives impact with the Earth's surface. One of famous: Allende Fell in Mexico in 1969 Huge fireball and shower of stones About 2000 kg of rock collected Sometimes angle of infall can be reconstructed from camera recordings. Orbit of meteorite can then be reconstructed. Meteorites often easier to find on ice fields on polar caps(Antarctica) complement

Meteorites Some meteorites originate from Mars or Moon Most meteorites were originally part of ~100 km sized planetesimals (`parent bodies’) that have fragmented. Some are from differentiated parent bodies: heat has melted the material: iron sunk to center: iron meteorites, basaltic meteorites. Most are from undifferentiated parent bodies: original build-up particles: – Chondrules (mm size spherules, <10 mm particles) – Matrix (`cement’ between chondrules) – Calcium-Aluminium-rich Inclusions (CAIs, cm size, rare) Chondrites

Chondrules+Matrix

Classes of Chondrites Chondrites (or ‘chondritic meteorites’) named after their abundant constituents: chondrules Two main classes of chondrites: – Ordinary chondrites (most abundantly found on Earth) – Carbonaceous chondrites: fewer chondrules, more matrix (30%-100%)

Properties of matrix Cement between chondrules Consists of micron size particles Often contains water and carbon Often contains hydrous ( 수화, 함수 ) minerals resulting from ancient interaction of liquid water and primary minerals: Must have been liquid water in planetesimals!

Properties of chondrules Rounded, once molten silicate droplets Their formation requires T>=1600K Their composition varies from meteorite to meteorite, but the average composition (chondrules+matrix) appears to be solar.

Temperature of the proto-planetary disk

Origin and Evolution of Life on Earth Materials in Earth should experience high temperature. A accretion models for the formation of the Earth and the single-impact theory of the origin of the Earth-Moon system predict a volatile-depleted young Earth. It suggested that the accumulation of the organic inventory of Earth was likely a mix of “exogenic” organics with those endogenically synthesized in the eardly atmosphere, or perhaps, in other terrestrial (or deep-sea).

Cretaceous ( 백악기 ) Tertiary ( 제 3 기 ) A Wyoming rock with an intermediate claystone layer that contains 1000 times more iridium than the upper and lower layers. It is likely that the Cretaceous-Tertiary (K/T) extinction was caused by an impact of large meteorite (Alvarez et al., 1980) or a comet (Davis et al., 1984). Extraterrestrial nonproteinic amino acids were found near the K/T 65 million year old boundary, which may be of ultimate cometary origin (Zhao and Bada, 1989; Zahnle and Grinspoon, 1990).

Zhao & Bada, Nature 339, (1989)

Murchison meteorite One of the most studied meteorites due to its large mass (>100 kg) Collected in 1969 Classified into carbonaceous chondrite This meteorite experienced extensive alteration by water-rich fluids on its parent body Over 100 amino acids (some of the basic components of life) have been identified in the meteorite, such as glycine, alanine and glutamic acid as well as unusual ones on the Earth

In amino acids there are two optical isomers ( 이성체 ), called L or D amino acids. They are mirror images of each other. L-amino acids represent all of the amino acids found in proteins. L-enantiomeric ( 거울상 ) excesses have been found in Murchison.

Miller–Urey experiment as an endogenous origin The Miller–Urey experiment was an experiment that simulated hypothetical conditions on the early Earth, and tested for the occurrence of chemical evolution. Specifically, the experiment tested a hypothesis that conditions on the primitive Earth favored chemical reactions that synthesized organic compounds from inorganic precursors.

The experiment used H 2 O, CH 4, NH 3, and H 2. The chemicals were all sealed inside glass tubes and flasks connected in a loop. There were two flask, one with half-full of liquid water and another containing a pair of electrodes. The liquid water was heated to induce evaporation, sparks were fired between the electrodes to simulate lightning through the atmosphere.

At the end of one week of continuous operation, Miller and Urey observed that as much as 10–15% of the carbon was now in the form of organic compounds. Two percent of the carbon had formed amino acids that are used to make proteins in living cells, with glycine as the most abundant. Sugars, liquids, and some of the building blocks for nucleic acids were also formed. Both left-handed (L) and right-handed (D) optical isomers were created in a racemic mixture (note that in nature, L amino acids dominate).