• What we think of as Lake Turkana has only been around for the past 200,000 years—the blink of an eye in geologic terms. The expanding and receding shores of the lake have provided food and water to organisms for millions of years.

    Today, scientists study the stratigraphy—layers of rocks and sediment—of the Turkana basin to better understand the age of fossils discovered there. Stratigraphy also provides clues to the ancient paleoenvironments these organisms encountered when they were alive.

    One of the earliest paleoenvironments of the Turkana basin was the Apak flood plain of the Pliocene epoch. Around 4.5 million years ago (mya), the ancestral Omo, Turkwell, and Keiro rivers joined to form the Turkana River. The Turkana is a “phantom river,” one scientists have never observed but is hypothesized to exist based on geologic and fossil evidence. For instance, the Turkana basin has yielded fossils of a whale and stingray, marine animals that have been known to swim upriver. This evidence suggests the “phantom” Turkana River may have had its mouth in the Indian Ocean.

    Later in the Pliocene (about 4.1 mya), a large body of water, Lonyumun Lake, covered the Turkana basin for about 100,000 years. Lonyumun Lake drowned many terrestrial habitats, such as forests and grasslands. The remainders of these habitats existed on the margins of the basin. The chief fossils found during the time of Lonyumun Lake have been fish and mollusks.

    Even later in the Pliocene (3.5 mya), a second body of water, Lokochot Lake, appeared and disappeared within 60,000 years. The most important fossil preserved by the sediments of Lokochot Lake is probably the extinct hominin Kenyanthropus platyops. K. platyops was related to human ancestors, and is important to the study of evolutionary patterns.

    Mount Kulal, an active volcano, dominated the landscape of the Turkana basin about 2.4 million years ago, during the late Pliocene and early Pleistocene. In fact, fossils unearthed in the Tulu Bor flood plain, which blanked the basin near Mount Kulal, are embedded in tuff, or hardened volcanic ash.

    Lorenyang Lake, a body of water formed during the Pleistocene (1.9 mya), was much longer-lasting than any other lake in the Turkana basin. Lorenyang Lake existed for about 400,000 years. Fossils of the Lorenyang Lake period are varied and rich, from hominins such as Homo habilis to organisms Homo habilis may have eaten: fish and shellfish, plants, and birds.

    Lorenyang Lake eventually filled with sediment and was succeeded by another flood plain, the Chari flood plain (1.5 mya). Fossilized footprints in the Chari flood plain help provide scientists with evidence that at least some hominins were walking upright at this time.

    The massive body of water that scientists call “Mega-Lake Turkana” emerged during the “African Humid Period,” about 9,000 years ago. The climate of the African Humid Period helped provide people with a rich array of resources: aquatic and wetland plant and animal species, a reliable source of freshwater, and “lush grasslands for hunters and fishers to utilize.”

    Mega-Lake Turkana dried up almost completely about 7,500 years ago. The lake probably split into two small, shallow bodies of water. Scientists look at this period in Turkana basin’s history for a possible glimpse of how the landscape may be transformed if Ethiopia proceeds with the planned construction of a massive dam on the Omo River, the major tributary to Lake Turkana.

    1. What are the names of three rivers that flow into modern Lake Turkana?

      The Omo, Turkwell, and Kerio Rivers flow into Lake Turkana.

    2. What clues do geologists look for to tell them that volcanoes were active in the Turkana Basin millions of years ago?

      Geologists study rocks called tuff, or hardened volcanic ash, that they can date using specialized tests.

    3. Fossils of which two extinct hominin species were found in the sediments deposited in Lorenyang Lake? Approximately how many years in the past were these sediments deposited and the fossils preserved?

      Fossils of Homo habilis and Homo rudolfensis were found in the sediment and date to approximately 2 to 1.6 million years ago.

    4. How do scientists and researchers reconstruct rivers and lakes as they appeared millions of years ago?

      Scientists look for clues in rocks and fossils that they can perform tests on to approximate an age of the rock or fossil. Certain types of rocks and fossils give scientists clues as to what the environment looked like in an area at a particular time in the past.

  • Term Part of Speech Definition Encyclopedic Entry
    active volcano Noun

    volcano that may erupt or has erupted regularly over time.

    basin Noun

    a dip or depression in the surface of the land or ocean floor.

    Encyclopedic Entry: basin
    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    dam Noun

    structure built across a river or other waterway to control the flow of water.

    evolution Noun

    process of how present types of organisms developed from earlier forms of life.

    expand Verb

    to grow.

    flood plain Noun

    flat area alongside a stream or river that is subject to flooding.

    Encyclopedic Entry: flood plain
    forest Noun

    ecosystem filled with trees and underbrush.

    fossil Noun

    remnant, impression, or trace of an ancient organism.

    Encyclopedic Entry: fossil
    geologic Adjective

    having to do with the physical formations of the Earth.

    grassland Noun

    ecosystem with large, flat areas of grasses.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    hominin Noun

    tribe of the hominid family of primates, distinguished by erect posture, bipedal movement, large cranial capacity, and use of specialized tools. Human beings are the only living hominins.

    hypothesize Verb

    to form a statement or suggestion that explains certain questions about certain facts.

    landscape Noun

    the geographic features of a region.

    Encyclopedic Entry: landscape
    mouth Noun

    place where a river empties its water. Usually rivers enter another body of water at their mouths.

    Encyclopedic Entry: mouth
    recede Verb

    to retreat or withdraw.

    river Noun

    large stream of flowing fresh water.

    Encyclopedic Entry: river
    rock Noun

    natural substance composed of solid mineral matter.

    sediment Noun

    solid material transported and deposited by water, ice, and wind.

    Encyclopedic Entry: sediment
    shore Noun

    coast.

    stratigraphy Noun

    the study of stratified, or layered, rocks.

    terrestrial Adjective

    having to do with the Earth or dry land.

    tributary Noun

    stream that feeds, or flows, into a larger stream.

    Encyclopedic Entry: tributary
    tuff Noun

    type of rock formed from hardened volcanic ash.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
Tell us what you think