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Conditions on Early Earth

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment.

Conditions on Early Earth

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment.

Eukaryotic Evolution

Eukaryotic Evolution

The endosymbiont theory is the most widely accepted theory of eukaryotic evolution; however, its progression is still somewhat debated. According to the nucleus-first hypothesis, the ancestral prokaryote first evolved a membrane to enclose DNA and form the nucleus. Conversely, the mitochondria-first hypothesis suggests that the nucleus was formed after endosymbiosis of mitochondria.
Contrary to the endosymbiont theory, the eukaryote-first hypothesis proposes that the simpler prokaryotic and...

Diversity of Protists I

Diversity of Protists I

Excavata is a diverse group of protists that includes both chemoorganotrophic and phototrophic species, with some thriving in anaerobic environments. Among the key groups within Excavata are diplomonads and parabasalids, which are flagellated protists that lack mitochondria and chloroplasts. These microorganisms typically inhabit anoxic environments, such as the intestines of animals, where they exist either symbiotically or as parasites, relying on fermentation for energy production. Some...

Diversity of Protists III

Diversity of Protists III

Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...

Origin of Photosynthesis

Origin of Photosynthesis

Photosynthesis represents a fundamental biological process that transformed Earth's atmosphere and paved the way for complex life. Emerging roughly 3.4–3.8 billion years ago, the earliest photosynthetic organisms harnessed light energy to produce organic compounds. These anoxygenic phototrophs used electron donors like hydrogen sulfide (H₂S) or ferrous iron (Fe²⁺), rather than water, and did not release molecular oxygen (O₂) as a byproduct. Various groups, including green sulfur and purple...

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Updated: Jul 11, 2026

Establishment of Microbial Eukaryotic Enrichment Cultures from a Chemically Stratified Antarctic Lake and Assessment of Carbon Fixation Potential

Establishment of Microbial Eukaryotic Enrichment Cultures from a Chemically Stratified Antarctic Lake and Assessment of Carbon Fixation Potential

Published on: April 20, 2012

¿Una lluvia de cometas o asteroides en el Eoceno tardío?

Roald Tagle¹, Philippe Claeys

¹Institut fuer Mineralogie, Museum fuer Naturkunde, D-10099 Berlin, Germany.

Science (New York, N.Y.)

|July 27, 2004

Resumen

Una lluvia de cometas puede no explicar los eventos de impacto del Eoceno de la Tierra. Nuevos análisis de elementos del grupo del platino sugieren que un meteorito L-condrita formó el cráter Popigai, desafiando la hipótesis de impacto cometario.

Área de la Ciencia:

Ciencias planetarias Ciencias planetarias.
Geología Geología Geología.
Cosmoquímica es la cosmoquímica.

Sus antecedentes:

El Eoceno tardío (aprox. Hace 35 millones de años) vio una gran afluencia de polvo interplanetario y la formación de dos cráteres de impacto masivos: Popigai y Chesapeake Bay.
Una lluvia de cometas ha sido la teoría predominante para explicar esta coincidencia.

Objetivo del estudio:

Para investigar el tipo de proyectil responsable del cráter Popigai.
Reevaluar la causa del aumento del flujo de material extraterrestre durante el Eoceno tardío.

Principales métodos:

Análisis de elementos del grupo del platino (PGE) de muestras de la estructura de impacto de Popigai.
Comparación de las firmas de PGE con las composiciones conocidas de meteoritos.

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Principales resultados:

Los análisis de PGE indican que el cráter Popigai se formó por el impacto de un meteorito de L-condrita.
Un proyectil de L-condrita es inconsistente con un origen cometario.
El alto flujo de materia extraterrestre puede tener una fuente diferente.

Conclusiones:

La formación del cráter Popigai por un meteorito de L-condrita desafía la hipótesis de la lluvia de cometas para los eventos de impacto del Eoceno tardío.
Una colisión importante dentro del cinturón de asteroides se propone como una causa más plausible para el aumento de la entrega de materia extraterrestre, incluido el polvo y los grandes impactos.