We study the homological properties of random simplicial complexes. In particular, we obtain the asymptotic behavior of lifetime sums for a class of increasing random simplicial complexes; this result is a higherdimensional counterpart of Frieze's ζ(3)-limit theorem for the Erdős-Rényi graph process. The main results include solutions to questions posed in an earlier study by Hiraoka and Shirai about the Linial-Meshulam complex process and the random clique complex process. One of the key elements of the arguments is a new upper bound on the Betti numbers of general simplicial complexes in terms of the number of small eigenvalues of Laplacians on links. This bound can be regarded as a quantitative version of the cohomology vanishing theorem.2010 Mathematics Subject Classification. Primary 05C80, 60D05; Secondary 55U10, 05E45, 60C05. Key Words and Phrases. Linial-Meshulam complex process, random clique complex process, multiparameter random simplicial complex, lifetime sum, Betti number. K n (t) decreases, and β 0 (K n (t)) denotes the zeroth (reduced) Betti number of K n (t), that is, the number of connected components of K n (t) minus one. This type of relation holds for a general increasing family of graphs. Applying this formula and analyzing β 0 (K n (t)) in detail, Frieze [7] obtained the following significant result about the behavior of W n .and for any ε > 0,Recently, there has been a growing interest in studying random simplicial complexes as a higher-dimensional generalization of random graphs. Since an Erdős-Rényi graph can be regarded as a one-dimensional random simplicial complex, and graph connectivity can be equivalently described as the vanishing of the zeroth (reduced) homology, it is natural to seek a higher-dimensional analogue to the theory of Erdős-Rényi's G(n, p) model. The d-Linial-Meshulam model [14] and the random clique complex model [12] are typical models of this type. The d-Linial-Meshulam model Y d (n, p) is defined as the distribution of d-dimensional random simplicial complexes with n vertices and the complete (d−1)-dimensional skeleton such that each d-simplex is placed with independent probability p. The random clique complex model C(n, p) is defined as the distribution of the clique complex of the Erdős-Rényi graph that follows G(n, p). Here, given a graph G, its clique complex Cl(G) is defined as the maximal simplicial complex among those for which the one-dimensional skeletons are equal to G. Linial, Meshulam, and Wallach [14,16] exhibited the threshold for the vanishing of the (d − 1)-th homology for the d-Linial-Meshulam model, which is analogous to the connectivity threshold of the Erdős-Rényi graph. Later, Kahle [13] obtained similar results for the random clique complex model.Along another line, Hiraoka and Shirai [10] obtained a higher-dimensional analogue of (1.1) in the context of the theory of persistent homology. Persistent homologies can describe the topological features of a filtration (i.e., an increasing family of simplicial complexes; see, e.g., [3,17]). In par...