"De Money series no. 1" by George Osodi is featured in “Earth Matters: Land as Material and Metaphor in the Arts of Africa,” at the Smithsonian’s National Museum of African Art from April 22 to Jan. 5. (George Osodi/National Museum of African Art)

There is a deeply appropriate resonance in the opening of “Earth Matters: Land as Material and Metaphor in the Arts of Africa” on Monday, Earth Day, at the National Museum of African Art.

It is a large-scale, ambitious joining of the conversation by artists singularly positioned to weigh in. African people have humanity’s longest-standing relationship to the planet, and the fact that they have been having artistic conversations about that relationship for centuries is one of the points the exhibition seeks to make clear.

The exhibition of 100 items that date back as far as 1800 includes work by 40 artists from 24 African nations and the African diaspora who draw on the land for inspiration. It includes five thematic sections: “Material Earth,” “Power of the Earth,” “Imagining the Underground,” “Strategies of the Surface” and “Art as Environmental Action.” A sixth section, featuring three commissioned earthworks, is a first for the Smithsonian Gardens and the Mall.

In Africa, says curator Karen Milbourne, “you know the concerns related to territorial disputes — extracting minerals to build an iPhone 5, how to dispose of the iPhone 4. Fundamental to every one of those is the human relationship to the land.”

“If we don’t understand that connection, how we move forward is flawed from the get-go,” she adds.

“Africa is the only cradle of humanity,” said museum director Johnnetta Cole. There have to be conversations about the universal connectedness to the place “where the first human beings had language and art.”

In a section on the material earth, early 20th-century iron, wood and a beaded fabric sheath represent the Yoruba deity Oko, who oversees farms, fields, planting and human fertility.

Photographer Helga Kohl’s work documents the homes, offices and shops in a once-thriving community around a diamond mine in Namibia, abandoned when the mine was exhausted. Kohl returned to the ghost town to chronicle the structures’ return to the earth as the surrounding sands swallow them.

In “Rain Horse,” ashes from apartheid-era South African atlases are combined with charcoal for the dust drawing of a crumbling horse, with a devastated landscape as its shadow. It is a way to think “of things that collapse, the remains that are left, not just on an individual basis, but the stains or traces that a population leaves on the land,” according to the artist, Diane Victor.

The power of the land — to heal, to bury, as sacred ground, as the frame to orient the days and lives of its people — is explored in mediums, masks, altar figures and paintings.

The centerpiece of the gallery features five reliquary figures from late-19th-century Gabon, for a grouping thought to be unique in the world. The figures, in which bark, wood and plant fibers are joined with bones and statuary, were intended to allow the living to communicate with the dead. Themes of being tied to the land are conveyed with bindings under the arms of the figures. Some of these representations fell out of favor as colonialism forced a renegotiation of land relations.

The limitlessness of the African underground is addressed in concepts of invisibility and the divine. They are layered by contemplations of mining and other practices that introduced altered visions of the underground, memory and loss.

A tiered funeral vessel, open at both ends, was a conduit for Kongo people to communicate with ancestors and the spirits of the land. There are mine employees, jobless youth searching for mine work and photographic dissections of mined lands; there are representations of the lost history that might lie beneath.

A mid-20th-century oil on canvas offers up a South African landscape devoid of people, waiting to be taken.

A table map is the backdrop for a piece exploring late-19th-century Europeans carving up Africa, and in a haunting photo, blue asbestos “fluff” blankets a South African field. In “Aesthetic Recycling,” a young Moroccan artist gathers, squeezes and compresses the plastic bags that litter urban and rural spaces and strings them together to approximate Muslim prayer beads.

Outside the museum, in the Smithsonian Gardens, earth artists explore the spice trade with large mapping pins. Near the Smithsonian Castle, a garden of rice has been planted in a carve-out of the word “hunger,” and there is a sculpture made out of rusted graters, once used to shred Nigerian cassava crops, and mirrors.

African artists have often been absent in conversations about histories and choices made in relationship to the land beneath our feet, says Milbourne. The goal of the exhibition is not to rewrite the history of modern land art, “but to question it.”

Earth Matters: Land as Material and Metaphor in the Arts of Africa

Opens Monday with Earth Day activities, including artist discussions and performances. Through Jan. 5. National Museum of African Art, 950 Independence Ave. SW. 202-633-4600, africa.si.edu.