.
Geologists have divided Earth history into units displayed in the geologic time scale (Table 1–1). The units are called eons, eras, periods, and epochs and are identified primarily by the types of life that existed at the various times. The two earliest eons, the Hadean and Archean, cover the first 2.5 billion years of Earth history.
Life originated during Archean time. Living organisms then evolved and proliferated during the Proterozoic Eon (protero is from a Greek root meaning “earlier” or
“before” and zoon is from the Greek word meaning “life”). However, most Proterozoic organisms had no hard parts such as shells and bones. Most were single
celled, although some multicellular organisms existed.
The Proterozoic Eon ended about 538 million years ago. Then, within an astonishingly short time—perhaps as little as 5 million years—many new species evolved.
These organisms were biologically more complex than their Proterozoic ancestors, and many had shells and skeletons. The most recent 13 percent of geologic time,
from 538 million years ago to the present, is called the Phanerozoic Eon (phaneros is Greek for “evident”). The Phanerozoic Eon is subdivided into the Paleozoic Era
(“ancient life”), the Mesozoic Era (“middle life”), and
the Cenozoic Era (“recent life”)
.
Geologists have divided Earth history into units displayed in the geologic time scale (Table 1–1). The units are called eons, eras, periods, and epochs and are identified primarily by the types of life that existed at the various times. The two earliest eons, the Hadean and Archean, cover the first 2.5 billion years of Earth history.
Life originated during Archean time. Living organisms then evolved and proliferated during the Proterozoic Eon (protero is from a Greek root meaning “earlier” or
“before” and zoon is from the Greek word meaning “life”). However, most Proterozoic organisms had no hard parts such as shells and bones. Most were single
celled, although some multicellular organisms existed.
The Proterozoic Eon ended about 538 million years ago. Then, within an astonishingly short time—perhaps as little as 5 million years—many new species evolved.
These organisms were biologically more complex than their Proterozoic ancestors, and many had shells and skeletons. The most recent 13 percent of geologic time,
from 538 million years ago to the present, is called the Phanerozoic Eon (phaneros is Greek for “evident”). The Phanerozoic Eon is subdivided into the Paleozoic Era
(“ancient life”), the Mesozoic Era (“middle life”), and
the Cenozoic Era (“recent life”)
.
» كلمات فرنسية من الحياة اليومية مترجمة إلى العربية
» Lesson Two الدرس الثانى
» دورة ICDL مبسطه
» فيديوهات دكتور إبراهيم الفقى كاملة
» Lesson Seven الدرس السابع
» All Medical Rep And Supervisor Pharmaceutical Companie PMR
» Lesson One الدرس الأول
» ترحيب بالأعضاء الجدد فى منتدى العالم العربى
» ما هو الحيوان الذى تخافه الجن
» Greetings and Courtesies : التحية و المجاملات
» شكر خاص لكل اللى ساهموا فى نجاح هذا الكورس التعليمى
» ألغاز العالم العربى
» بإمكان مصر انت تصبح اغنى دول العالم واغنى من دول الخليج . بحث للدكتور نادر نور الدين
» زوج يرسل إيميل بالغلط
» عناوين شركات البترول فى مصر
» Lesson Four الدرس الرابع
» دكتور إبراهيم الفقى - سلسة قوة الثقة بالنفس
» مقياس الحقيقة
» نكت جااااااااااااامدة